The GWverse and black-hole blues
2021-08-30 09:00 - 18:00 UTC | Academia de Ciências de Lisboa
In 2016, a short time before the announcement of the first gravitational-wave detection, a cross-disciplinary initiative in Europe led to the establishment of the new CA16104 COST networking Action on Black holes, gravitational waves and fundamental physics (GWverse). GWverse, chaired by Prof. Vitor Cardoso, aims to maintain and consolidate leadership in black-hole physics and gravitational-wave science. The Action supports the training of the next generation of leaders in the field, and the very first “native” GW/multi-messenger astronomers, ready to tackle the challenges of high-precision GW astronomy with ground and space-based detectors.The fourth and final global meeting of the Action will be a hybrid meeting. The meeting will be remote (via Zoom), with its core programme taking place in the afternoons, from 30 Aug – 03 September 2021. However, for those willing and able to be in Lisbon in person, there will be additional sessions in the morning in the wonderful Academy of Sciences of Lisbon. A meeting of the Board of the Action is scheduled for the morning of Aug 30.The first day of the meeting includes a public talk (at 16:00 PT) by well-known scientists Janna Levin (Columbia University) and Pedro G. Ferreira (Oxford University). To join this public event, please click https://us02web.zoom.us/j/83173449837.Brief Bio of Janna Levin and Pedro G. FerreiraJanna Levin is the Tow Professor of physics and astronomy at Barnard College of Columbia University. She has contributed to an understanding of black holes, the cosmology of extra dimensions, and gravitational waves in the shape of spacetime. Among other prizes she has been named a Guggenheim Fellow. She is also director of sciences at the cultural center Pioneer Works and the editor-in-chief of The Broadcast. Her previous books include How the Universe Got Its Spots and a novel, A Madman Dreams of Turing Machines, which won the PEN/Bingham Prize. Her book, Black Hole Blues and Other Songs from Outer Space, is the inside story on the discovery of the century: the sound of spacetime ringing from the collision of two black holes over a billion years ago. Her most recent book is Black Hole Survival Guide.Pedro G. Ferreira is Professor of Astrophysics at the University of Oxford. He studied and worked at Imperial College in London, at the University of California at Berkeley and at CERN in Geneva. He has held visiting positions at University of Edinburgh, at the Albert Einstein Institute in Berlin and at Columbia University in New York. His area of expertise is cosmology where he has pioneered research in the relic radiation left over from the Big Bang, the nature of the dark Universe (such as dark matter and dark energy) and has led the way in studying alternatives to Einstein’s theory of General Relativity. He has published over 200 papers and has delivered over 100 talks at universities, institutes and conferences all over Europe, America, Asia and Africa. Pedro has written extensively outside academia, writing for Nature, Science, New Scientist, Physics World, Physics Today, Scientific American, Sky at Night, CERN Courier, BBC Focus, The Guardian. His most recent book, “The Perfect Theory: A Century of Geniuses and the Battle over General Relativity” has been published in over 20 countries and was shortlisted for the 2014 Royal Society Winton Science Book Prize.

Boas vindas a novos membros
2021-09-14 16:00 - 18:00 | Sala de seminários do DF
O Departamento de Física vai apresentar os novos membros à família DF. A cerimónia formal de apresentação será virtual, mas com direito a um copo de champagne celebratório real. Os novos colegas do nosso Departamento serão introduzidos pelo coordenador da respectiva área, e depois dir-nos-ão um pouco acerca de si mesmos.

The gravity of classical fields
2021-09-21 14:00 - 17:00 | Técnico
Rodrigo Vicente will defend his PhD work on "THE GRAVITY OF CLASSICAL FIELDS", done under supervision of Prof. Vítor Cardoso. The jury members are Richard Brito (Técnico, referee), Katy Clough (Oxford, referee), Lam Hui (Columbia University), José Natário (Técnico) and Vítor Cardoso (Técnico). The committee is presided by José Lemos (Técnico).

Recepção às famílias
2021-10-02 09:00 - 13:00 | Campus da Alameda
O Departamento de Física organiza uma recepção às famílias dos estudantes que este ano ingressaram em Física. O curso de Física está mais uma vez no topo das preferências dos alunos mais talentosos do país, muitos dos quais são oriendos dos mais variados pontos de Portugal. O Professor Luís Oliveira e Silva fará uma pequena visita guiada à Escola, passando pelos principais pontos de referência e esclarecendo quaisquer dúvida. Bem-vindos a todos ao DF.

Recepção aos novos alunos
2021-10-15 17:00 - 18:00 | Salão Nobre, Edificio Central
O DF vai dar as boas vindas aos novos alunos do LEFT e MEFT, dia 15 de Outubro. A recepção vai incluir uma descrição do departamento e dos eventos mais extraordinários dos últimos anos. Durante este evento, vamos ouvir ex-alunos do DF, incluindo Helvi Witek (actualmente professora na Universidade de Urbana-Illinois nos Estados Unidos), e alunos actuais como o José Figueiredo. Vamos convidar o NFIST a mostrar-se e as novas caras do DF a apresentarem-se. E temos uma surpresa para todos.

Spacetime Geometry of Rotating Boson Stars and KBH
2021-11-11 14:30 - 15:30 | Sala de seminários do DF
The theory of a complex scalar field minimally coupled to gravity allows for amusing stationary configurations that defy common intuition built upon our knowledge of more conservative compact objects. Upon rotation, the topology of the scalar field changes and the solution possesses an offcenter distribution of energy density. In turn, the metric potentials behave nonmotonically with increasing radial coordinate, deviating considerably from external Kerr. In this talk we shall explore the spacetime structure of rotating boson stars (BSs) and Kerr black holes with scalar hair (KBHsSH) and address peculiar properties of circular orbits on their equatorial plane, as well as some astrophysical implications to accretion discs and inspirals. Furthermore, by attempting a fluid description of the complex scalar field, we will unveil a strange connection between a BS co-moving observer and the synchronization condition for KBHsH.

Development of GPU-accelerated trigger algorithms for the ATLAS experiment at the LHC
2021-11-16 09:00 - 11:00
(Contactar Ana Bela Cardoso para password)ana.bela.cardoso@tecnico.ulisboa.pt

Scalar Mixing in New Physics Models
2021-11-17 09:00 - 11:00

Experimental investigation and kinetic...
2021-11-18 14:00 - 16:00 | Sala C10, Pavilhão Central, 1º piso
Experimental investigation and kinetic modeling of CO2-CH4 plasmas (mestrado)

Towards a distributed magnetic tactile...
2021-11-18 14:00 - 16:00
Towards a distributed magnetic tactile sensor network for flexible skin (mestrado)

Confronting Multi-Higgs models with experiment: The Search for Underrated and Understudied Signals (mestrado)
2021-11-23 08:30 - 11:00 | https://videoconf-colibri.zoom.us/j/87847848381?pwd=[REDACTED]

Some Theoretical Aspects of Multi-Higgs Doublet Models
2021-11-23 10:30 - 13:00 | https://videoconf-colibri.zoom.us/j/87847848381?pwd=[REDACTED]

Polarimetric Studies of Galaxies
2021-11-23 17:00 - 19:00 | Sala de Formação Avançada do DF - piso 2

Testing General Relativity at the galactic centre
2021-11-24 10:00 - 11:00 | seminar room, physics department
PhD student Arianna Foschi will discuss her thesis work on strong-field gravity. The thesis supervisor is Prof. Vítor Cardoso. The Commission accompanying the PhD work (CAT) is composed of members: V. Cardoso, P. Garcia, A. Maselli, and I. Lopes (president).

Voltage dynamics and statistics in balanced networks
2021-11-24 14:30 - 16:00 | https://videoconf-colibri.zoom.us/j/85113082888?pwd=[REDACTED]

Lyapunov-Governed Magnitude-Independent Average Fidelity Decay in a Classically Mixed Two-Spin System
2021-11-25 10:00 - 12:00 | https://videoconf-colibri.zoom.us/j/87954064199?pwd=[REDACTED]

From light-front wave functions to parton distribution functions
2021-11-25 10:00 - 12:00 | https://videoconf-colibri.zoom.us/j/83168427728?pwd=[REDACTED]

Probing multiparticle production properties of the first ultra-high energy cosmic ray-Air interaction in Extensive Air Showers with low muon content
2021-11-25 11:30 - 13:00 | Online

The large D limit of General Relativity
2021-11-25 14:30 - 16:00 | Sala de seminários do DF
Speaker: Raimon Luna (CENTRA)Title: "The large D limit of General Relativity"Abstract:In this seminar I will give an overview of the recent developments in the Large D limit of gravity. In this approach, we explore the limit General Relativity as the number of dimensions grows very large, which allows us to perform perturbative analysis with asymptotic expansions in powers of 1/D, with D being the dimension of spacetime. This makes it possible to access analytically (or with very modest numerical techniques) the physics of black holes, both in D=4 and in higher dimensions. In particular, I will focus on the effective theory for black holes with extended directions (mainly black strings and black branes) which has been used to recover the critical dimension of black strings, and most importantly to predict violations of Penrose's Weak Cosmic Censorship conjecture in black hole mergers through the so-called blobology formalism.For those who cannot attend the seminar in person, we will also broadcast it through zoom: https://videoconf-colibri.zoom.us/j/85037094360?pwd=[REDACTED] organizer for password. Organizer: Alex Vano-Vinuales (alex.vano.vinuales@tecnico.ulisboa.pt)

A novel energy reconstruction for high-energy gamma-ray wide field of view observatories
2021-11-25 15:00 - 17:00 | https://videoconf-colibri.zoom.us/j/83608217848?pwd=[REDACTED]

Growth of noble metal Au-Nano particles into selected dielectric matrixes
2021-11-25 15:30 - 16:30 | Online

Evolution of Dipolar Boson Stars and Head-on Collisions of Spherical Boson Stars
2021-11-26 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso

Cr-doped β-Ga2O3 for radiation detection
2021-11-29 11:00 - 13:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)

A hidden, heavier resonance of the Higgs field
2021-11-30 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Spontaneous symmetry breaking is an essential ingredient of the Standard Model. While Goldstone bosons are well understood, stillthe ultimate dynamical origin of the phenomenon is not entirely clear. Given this uncertainty, one may wonder about the present view that the Higgs-field propagator has only one pole at 125 GeV. In fact, depending on the description of symmetry breaking, the effective potential, besides the mass scale describing its quadratic shape at the minima, could exhibit another mass scale associated with the zero-point energy, which determines its depth. Lattice simulations of the propagator are consistent with this two-mass structure and can be used to predict a new resonance around 700 GeV. In spite of its large mass, however, the heavier state would couple to longitudinal Ws with the same typical strength of the low-mass state and thus represent a relatively narrow resonance. In this way, such a hypothetical resonance would naturally fit with some excess of 4-lepton events observed by ATLAS around 680 GeV. Available CMS data in the same region, when grouped in bins of 30 GeV as done by ATLAS, are also consistent with this interpretation. Implications of this two-mass structure for radiative corrections will also be discussed.

Plasmonic instabilities in two-dimensional Dirac materials
2021-11-30 16:00 - 18:00 | Auditorium/Room 9 @ INESC
The generation of coherent terahertz radiation is an outstanding challenge at both scientific and technological levels. In one hand, the quest for table-top THz solutions based on integrated-circuit technology puts graphene and other bi-dimensional in the run; on the other, plasma instabilities in bi-dimensional materials are an appealing mechanism for the production of low-power coherent THz signals. In this talk, we discuss how to produce plasmonic instabilities in graphene field-effect transistors based on electronic injection only.

A First Sample of Dust Attenuation Laws for DES Galaxies
2021-11-30 17:00 - 19:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)

Charged dark matter
2021-12-02 14:30 - 16:00 | Sala de Seminários do DF (2-8.3) 2º Piso
Is it possible to have long range forces competing with gravity at large, astrophysical and cosmological scales? The unknown nature of the dark sector allows to speculate on this possibility. In this talk I will present a model in which a universally charged dark matter component has this property. This scenario comes equipped with a natural screening mechanism a là K-mouflage thus avoiding traditional constraints on this kind of forces. After introducing the model properties, I will focus on its phenomenology. In particular, I will show how an inhomogeneous cosmological model is dynamically generated and explore its connection with the Hubble tension and astrophysical bodies dynamics. Finally, I will briefly discuss how further constraints on the model can be cast by considering the linear response of charged objects under an external static field.

Michelson Morley Experiments: Crossroads of Relativity, Cosmology and Quantum Theory
2021-12-02 16:00 - 18:00 | Anfiteatro Abreu Faro
In 1887 Michelson and Morley tried to observe in laboratory the "ether wind" by measuring a small difference in the velocity of two perpendicular light beams. Their measurements being much smaller than the classical expectations, the experiment was interpreted as a null result. This was crucial for the first pioneering formulations of the relativistic effects and represents a fundamental step in the history of science. Since then, more and more precise repetitions of that original experiment have been performed and the standard conclusion has been always the same: no genuine ether wind has ever been detected.However, if the velocity of light in the various interferometers is not exactly the same parameter "c" of Lorentz transformations nothing would prevent in principle a non-zero effect. For instance, in a gaseous medium the small fraction of refracted light could keep track of the motion of matter with respect to some preferred reference frame. Starting from this observation, there is now a new interpretation where the small irregular residuals observed in laboratory show surprising correlations with the direct observations of the Cosmic Microwave Background (CMB) with satellites in space. This opens the possibility of finally linking the CMB with a fundamental reference system for relativity with substantial implications for the interpretation of non-locality in the quantum theory. The Colloquium will focus on the essential aspects of this research with brief historical notes on some leading scientists involved in these measurements.

Novel Optimization Strategies for Clinical FLASH Proton Therapy. Evaluation on stereotactic lung treatment plans
2021-12-03 09:00 - 11:00 | https://videoconf-colibri.zoom.us/j/83608217848?pwd=[REDACTED]

Towards time ordered parton showers
2021-12-06 09:00 - 11:00 | Online
https://videoconf-colibri.zoom.us/j/83608217848?pwd=[REDACTED] Ana Bela Cardoso para password)ana.bela.cardoso@tecnico.ulisboa.pt

Modular Symmetries and the Flavour Problem
2021-12-06 09:30 - 11:00 | https://videoconf-colibri.zoom.us/j/87847848381?pwd=[REDACTED]

End-to-end simulation of satellite based quantum key distribution
2021-12-06 16:00 - 18:00 | https://videoconf-colibri.zoom.us/j/87311935352?pwd=[REDACTED]

Frequency resolved optical gating for ultrashort mid-infrared laser pulses
2021-12-07 09:30 - 11:30 | Online

Development of a trigger system for the ESTHER Shock Tube Spectroscopy/Streak-Camera Diagnostic
2021-12-07 16:00 - 18:00 | Online

Development of a magnetic camera for barcode and QR magnetic Identification tag readout
2021-12-07 16:30 - 18:00 | Online

Nonlinear optics with ultrashort mid-infrared laser pulses
2021-12-09 10:00 - 12:00 | Online

PALS – Setup optimisation and application to macromolecular materials characterisation
2021-12-09 10:00 - 12:00 | Online

A Computational Model for Radiotherapy Studies with Proton and Carbon ion Mini-Beams
2021-12-09 14:00 - 16:00 | Online

Classical and Quantum simulation of Extreme Plasma Physics
2021-12-09 14:00 - 16:00 | Online

Observers in black hole spacetimes: The inside story
2021-12-09 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
We consider several different aspects connected with properties of the motion of observers and particles inside the event horizon of a Schwarzschild black hole. We elucidate (i) how to maximize the observer's survival proper time and (ii) how to make the visible part of the outer universe as large as possible before the observer hits the singularity. We also consider the red and blueshifts of photons experienced by observers during their travel. We develop an approach that relates these properties with the formalism of particle collisions in a black hole spacetime and we show that for a special class of observers, the ones with zero momentum, there exists an analogue of the Banados-Silk-West effect inside the horizon.

Use of MHD Activity for Disruption Prediction in Tokamaks
2021-12-09 17:00 - 19:00 | Online

Dynamical bosonic stars and gravitational waves
2021-12-15 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Bosonic stars are theoretical exotic compact objects made of ultralight bosonic particles that could explain part of dark matter. In this talk, I will review some recent results on the stability and dynamical formation of these objects. Then I will talk about bosonic star mergers, the emission of gravitational waves, and what we could learn about them from a real gravitational wave event, if these stars exist in the Universe.

Evolution of the impact of oil prices on electricity, natural gas, and coal prices: causality and interaction
2021-12-15 14:30 - 16:30 | Online

Using atom-like spins in semiconductors toward scalable quantum computing
2021-12-15 16:00 - 18:00 | (Online): https://videoconf-colibri.zoom.us/j/83876336173?pwd=[REDACTED]
Password: [REDACTED] a world where the amount of data to process is steadily increasing, the quantum nature of matter offers new possibilities to develop concepts, which may overcome nowadays technologies. Implications are expected in research areas that can range from quantum computation, cryptography, and quantum simulation.To be useful, a qubit (the elementary quantum unit of information) needs to be both isolated from its environment and precisely controllable, which places strict requirements on its physical realization. In particular, spins in solids are one of the most promising realizations due to their potential for scalability and miniaturization. Furthermore, in these systems, quantum control has been established and electron spin coherence times now exceed several seconds. Even so, a critical challenge in these systems consists of developing a robust two-qubit gate that can be scaled up to a larger network.In this seminar, I will overview some of the challenges of this field and introduce a new mechanism for "long-range" interaction. Making use of independent readout of two electron spins, we demonstrate coherent exchange interaction mediated by a multielectron quantum dot. This result provides a possible route to the realization of multi-qubit quantum circuits based on single spins.Short bio: My research activities have mostly centred on the physics of nano-devices, and, in particular, on giving a direct and "local" understanding to a significant number of fundamental phenomena through experiments dealing with electron quantum interference and correlations, Coulomb blockade, and the quantum Hall regime. After 2015, my work has focused on implementing "spin qubits", i.e. units of quantum information represented by isolated spins confined in solid-state systems. In the course of my career, I have carried out research in laboratories worldwide including France, Belgium, Denmark, Australia, and Austria. In December 2020, I have joined the Quantum Information Team at the Hitachi Cambridge Laboratory (UK).

Quantum algorithm for the classification of Supersymmetric top quark events
2021-12-15 16:30 - 18:00 | Online
The search for supersymmetric particles is one of the major goals in the next high luminosity phase of the Large Hadron Collider. Supersymmmetric top (stop) searches play a very important role in this respect, but the unprecedented collision rate that will be attained at this phase poses new challenges for the separation between any new signal and the Standard Model background. While classical multivariate techniques might be insufficient in this new environment, the massive parallelism provided by quantum computing techniques may yield an efficient solution for the problem. In this paper we make a novel application of the QAML-Z approach to classify the stop signal versus the background, and implement it in a quantum annealer machine. We show that this approach together with the pre-processing of the data with Principal Component Analysis may yield better results than conventional multivariate approaches

Prescription for finite oblique parameters S and U in extensions of the SM with mW != mZ cos thetaW
2021-12-16 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Meeting ID: 849 8854 1912Meeting password: [REDACTED] consider extensions of the Standard Model with neutral scalars in multiplets of SU(2) larger than doublets. When those scalars acquire vacuum expectation values, the resulting masses of the gauge bosons W± and Z0 are not related by mW = mZ cos thetaW. In those extensions of the Standard Model the oblique parameters S and U, when computed at the one-loop level, turn out to be either gauge-dependent or divergent. We show that one may eliminate this problem by modifying the Feynman rules of the Standard Model for some vertices containing the Higgs boson; the modifying factors are equal to 1 in the limit mW = mZ cos thetaW. We give the result for S in a model with arbitrary numbers of scalar SU(2) triplets with weak hypercharges either 0 or 1.

Inference with core-collapse supernova waveforms
2021-12-16 14:30 - 16:00 | Sala de Formação Avançada, 2-8.11, Pavilhão de Física, 2º piso
Parameter estimation of core-collapse supernovae (CCSN) is challenged by the unmodeled nature of postbounce gravitational waveforms and by the intrinsic difficulties involved in the modeling of explosions of massive stars. Asteroseismology of proto-neutron stars (PNS) may offer a promising approach to do so. Numerical simulations of CCSN show that g-modes are commonly excited in PNS and they are responsible for a significant fraction of the gravitational-wave signal produced by most (i.e. neutrino-driven) supernova explosions. The time-frequency evolution of those modes is linked to the physical properties of the PNS through quasi-universal relations. This talk discusses recent work aimed at inferring PNS properties through the analysis of its modes of oscillation and the gravitational waves they trigger. Observational constraints of our findings for current and third-generation gravitational-wave detectors are reported. In the last part of the talk we will also cover recent results for the rather specific case of rapidly-rotating CCSN.

Quantum Link Prediction in Complex Networks
2021-12-17 09:00 - 11:00 | Online
Password: [REDACTED] ID: 836 1514 8258Predicting new links in physical, biological, social, or technological networks has a significant scientific and societal impact. Network based link prediction methods utilize topological patterns in a network to infer new or unobserved links. Here, we propose a quantum algorithm for link prediction, QLP, which uses quantum walks to infer unknown links based on even and odd length paths. By sampling new links from quantum measurements, QLP avoids the need to explicitly calculate all pairwise scores in the network. We study the complexity of QLP and discuss in which cases one may achieve a polynomial speedup over classical link prediction methods. Furthermore, tests with real-world datasets show that QLP is at least as precise as state-of-the-art classical link prediction methods, both in cross-validation tests and in the prediction of experimentally verified protein-protein interactions.

Dia do DF
2021-12-17 17:00 - 19:00 | Teatro Thalia
O Departamento de Física celebrou 40 anos em 2020, mas está maior e mais dinâmico que nunca. Nesta cerimónia anual vamos rever e celebrar o ano corrente, homenageando membros e alunos do DF. A fechar, haverá um momento musical com o pianista Filipe Pinto-Ribeiro.

Novel architectures to integrate ultra sensitive sensors to detect biomedical signals
2022-01-11 14:30 - 16:30 | Online
Magnetic sensing technologies are widely used in biomedical applications wherein magnetoresistive sensors are stated due to a high performance in terms of signal-to-noise ratio, power consumption and production cost. Furthermore, they work at room temperature with an established nTesla minimum field detectable at low frequencies. However, an improvement on the limit field detection can push forward the magnetoresistive technology as a high precision tool within the sub-nT field range. The key parameters of the magnetoresistive sensor performance are given by sensitivity, noise, power consumption, thermal and magnetic robustness. A proper multilayer stack engineering focused on materials and thicknesses of the buffer layer (Ta, NiFeCr), antiferromagnetic material (MnNi, MnIr), reference structure (exchange bias, synthetic antiferromagnet) and sensing layer can deliver an enhanced response according to the application requirements. Instead of a sensitivity enhancement driven by a higher MR ratio, the incorporation of magnetic flux concentrators provides a reduction of the linear range. However, the operational point of the latter approach is usually deviated from zero field due to its high sensitivity and hysteresis, being explored a monolithic biasing technique to compensate the shift of the output curve through the integration a current line directly on chip. On the other hand, the optimization of the minimum field detectable can also be delivered by a noise level reduction. Therefore, a vertical deposition of Z spin valve levels was assessed in order to achieve a compact parallel configuration with an equivalent resistance reduced by a factor of 1/Z. This work comprised the optimization of the deposition and microfabrication process for a thick multilayer stack; development of simulation and calculation tools to understand the physics behind and to support the device design; magnetic, magnetotransport and noise characterization of the microfabricated devices, and implementation of an experimental set-up to find the minimum field detectable within an unshielded environment. Packed devices composed of up to 50 spin valves vertically deposited and large sensing areas (low aspect ratio) led to a low nominal resistance combined with a linear and centered output driven by all magnetostatic couplings between ferromagnetic layers. This approach minimizes the noise level while maintaining a high sensitivity delivering an improved detectivity without compromising the device footprint. A 3D architecture design integrating magnetic tunnel junctions was pursued to push forward the detectivity of tunnel magnetoresistive sensors. The concept was demonstrated with a CoFeB/MgO/CoFeB based stack, being established a microfabrication process for a device composed of 3 levels. The characterized device presents a low noise level in addition to a high electrical robustness and compact footprint.

Optics in Wonderland: Down the rabbit hole of metaresonators
2022-01-12 16:00 - 18:00 | Online
Optical resonators allow the generation and storage of electromagnetic waves. They are widely used in technology and fundamental research, notably for their application in telecommunications, lasers and nonlinear optics, ultra-sensitive measurements in cavity optomechanics and the study of light-matter interactions. To some extent, it is possible to create structured light, i.e., to customize it by controlling its amplitude, phase, frequency, and polarization, directly inside a resonator, but the typical approaches used since the invention of the laser, such as pump shaping and designing different cavity geometries, are macroscopic and rather limited. In my most recent research, I have explored new cavity configurations incorporating metamaterials with structured elements smaller than the wavelength of light, allowing light to be shaped in unprecedented ways. These demonstrations range from embedding a mode converter inside a solid-state resonator to create tunable optical vortex arrays, to the use of mode converters as one or both cavity reflectors in external cavity lasers and silicon-on-insulator waveguides to enable lasing on holograms and create arbitrary near fields, to the monolithic integration into semiconductor lasers to engineer the spectrum of optical frequency combs. In all these cases, internal mode conversion confers intriguing new properties to these metaresonators, which cannot be derived from the properties of the base materials constituting the gain or waveguide medium, nor from the cavity geometry. In this seminar, I will provide an overview of this emerging field combining resonators with customized intracavity optical elements, which is one of the most complex and richest frontiers in optics.Bio: Marco Piccardo is a Researcher at the Istituto Italiano di Tecnologia in Milan leading a small team within the Vectorial Nano-Imaging research line. He is exploring novel approaches for structured light based on metasurfaces and their integration in active laser resonators. He is also an Associate Researcher at Harvard University, where he did his postdoctoral studies from 2016 to 2020 exploring new electronic and photonic properties of integrated laser frequency combs. He obtained his Ph.D. in Physics in 2016 from Ecole Polytechnique working on the fundamental electronic processes responsible for the efficiency drop of blue light-emitting diodes at high-current operation, such as Anderson localization and Auger recombination. He received his B.Sc. in Physics from Università degli Studi di Torino, and a M.Sc. in Physics from Ecole Normale Superieure and Ecole Polytechnique.

Magnetic field sensors for high precision surface scanners
2022-01-18 13:00 - 15:00 | Online
Abstract: The new technical paradigm of Industry 4.0 has been pushing the sensor technology, instrumentation, and measurement science to continue the progression of achieving the control and efficiency over the entire mass production process. Therefore, the development of smart and autonomous systems has led to a high demand of sensors for the monitorization of angular and linear positioning among the industrial, automotive and robotics market.The main limitations of the existing magnetic sensing technology based on state-of-art anisotropic magnetoresistive and hall effect sensors for incremental and absolute positioning systems rely on a low reading distance and a minimum pole pitch size down to 500 µm, which leads to a lower resolution and accuracy when compared to optical based encoders. The recent developments on magnetoresistive sensor technologies provide a competitive and reliable solution for the next generation of motion systems based on magnetic encoders, where the high signal-to-noise ratio and the enhanced spatial resolution of tunnel magnetoresistive sensors (TMR) can promote the detection of sub-100 µm pole pitch dimensions, driving to a performance similar to low-level optical encoders in terms of accuracy but with a lower production cost, enhanced working distance, reduced mounting tolerances and higher robustness to harsh environments. Therefore, following the technological trend observed in the hard disk devices, the development of the new generation of incremental magnetic encoders based on the TMR sensing technology focused on the (i) enhancement of the device reading distance beyond a gap equivalent to 1x pole pitch dimension and on the (ii) improvement of the accuracy employing (a) commercial elastomer bonded ferrite linear scales from a sub-100µm to a 5 mm pole pitch range and (b) microfabricated thin film magnetic scales based on a pole-groove pattern with a sub-500 µm pole pitch range.The optimization of the sensing technology, the sensor arrangement and packaging method delivered a successful outcome for a future short-term breakthrough on the available encoder solutions by achieving an accuracy around 3 µm at a reading distance of 1x for a pole pitch of 80 µm. On the other hand, a reading distance range around 3x was achieved for standard pole pitch dimensions, being able to reduce the mounting requirements in non-accurate applications.

Photoinduced dynamics of electronic, structural and magnetic order in quantum materials
2022-01-19 16:00 - 18:00 | Online (Password: [REDACTED]
Abstract:Quantum materials exhibit a variety of different phases that arise from the competition between different degrees of freedom – electronic, structural, spin and orbital. Ultrafast techniques enable a selective investigation of the dynamical response of these different subsystems through a careful choice of pump and probe characteristics.I will present results of studies in different quantum materials using ultrafast pulses in the optical, THz and x-ray frequency ranges.TbMnO3 is a prototypical multiferroic, where ferroelectric polarization arises from a cycloidal magnetic order below 27 K. The prospect of electric field control of magnetization dynamics makes multiferroic systems extremely appealing, in particular in the context of ultrafast magnetic switching. Using ultrafast x-ray pulses we have investigated the magnetic order and structural dynamics in TbMnO_3 following optical and THz excitation, shedding light onto the demagnetization pathways in this system.Mott insulators are archetypal examples of quantum materials, which have generated strong interest due in part to the insulator-to-metal transition that some exhibit when the balance between on-site Coulomb repulsion and hopping is overturned. Some Mott insulators exhibit an abrupt drop in resistivity under the application of electric fields with durations of a few tens of microseconds, with typical threshold fields on the order of 1-10 kV/cm. Quasi-dc electric fields well in excess of 1 – 10 kV/cm can currently be generated with ultrashort pulses in the low frequency or THz range, which enables the investigation of the sub-picosecond dynamics of the electric field driven Mott transition. I will present our results on THz driven dynamics in GaTa_4Se_8, a Mott insulator which exhibits clear electrical Mott transitions.Short Bio:Elsa Abreu is a Senior Research Assistant in the Physics Department of ETH Zürich. In 2018 she was awarded a four-year Ambizione Grant from the Swiss National Science Foundation for her project on "Exploring superconductivity pathways in low-dimensional spin-ladder and spin-chain compounds", and has since then been leading a team as a part of the Ultrafast Dynamics Group.She obtained her BSc in Physics from the Instituto Superior Técnico and her MSc at Instituto Superior Técnico and Uppsala University, Sweden. In 2014 she graduated with her PhD in Physics from Boston University, MA, USA, and then moved to Switzerland to work as a postdoctoral fellow at ETH Zürich.

Assessment of reflectometry diagnostics for DEMO
2022-01-26 09:00 - 11:00 | Online
Abstract: DEMO will be the first prototype of a fusion power plant. Unlike experimental tokamaks, only the necessary diagnostics for machine protection and plasma control will be implemented. One of the fundamental measurements is the position and shape of the last closed magnetic surface, typically measured with the magnetic diagnostics. One of the major issues of its implementation in DEMO is the large integration drifts that can occur during the operation due to the high levels of radiation. This can lead to a wrong plasma position estimation, putting the operation at risk.The prime candidate to complement or substitute the magnetic diagnostics in DEMO is the microwave reflectometry. By sweeping the frequency of the probing beam, microwave reflectometry is capable of measuring the electron density profile. As the density is directly linked to the magnetic flux surfaces these measurements give access to the magnetic configuration, providing its local radial position. The O-mode propagation is independent from the magnetic field, being ideal for replacing the magnetic diagnostics.The DEMO plasma position reflectometer (DEMO PPR) consists a system of multi reflectometers distributed poloidaly along the wall at different positions that will provide the separatrix reconstruction. The optimization of such system requires the simulation of the measurement process for different poloidal views, emitting angles, antenna assemblies and plasma configurations. The final system must be optimized for the operation scenario and be stable under the possible deviations to its equilibrium that can occur during the discharges. This includes the plasma displacement, turbulence or MHD activity. For now, the DEMO PPR is in an early development stage and there are many questions that need to be investigated before reaching its final design.In this work we study the process of optimization of PPR systems with a general approach, taking into account the future changes in the geometry and plasma scenario. The important variables of a general multiple reflectometers system were identified and the techniques and the procedure to optimize it were developed. The simulation of such systems is in general a complex task that requires the definition of several different regions of interest and testing different antenna models and plasmas, which is a very demanding task from the computational point of view and of necessary time to build the simulation scripts. For this reason, we develop the structure of a high-level framework for multiple reflectometry simulations that is capable of automatizing all the simulation process of a multiple reflectometers system for the REFMUL* codes, a family of full wave FDTD codes that has been used for reflectometry simulations. The user defines the configuration files of the system geometry and plasma, the probing bands and the dependence between the main variables of the problem. A script creates all the necessary models and scripts that to run all the simulations in the HPCs.Using the developed framework, we optimized the DEMO PPR system using the official DEMO scenario from EUROFUSION. We started by defining 100 different positions around the tokamak and testing two different configurations. In the first one, the antennas were aligned perpendicularly with the wall. This configuration has advantages from the point of view of the implementation of the antennas. However, the results shown that there are positions in the top of the machine and in the divertor region that have a very poor measurement performance and in some cases the signal is totally lost. In the second configuration, the antennas were aligned perpendicularly to the separatrix. In this case, since the direction of the probing beam is approximately parallel to the density gradient, a better measurement performance is expected. The results confirmed this principle, improving the results in several positions. At the divertor region, some of the positions continued to have a poor measurement performance, being necessary to sweep the probing angle to verify if there is an optimized configuration.One of the problems associated with the optimization is that is necessary to extract the round trip group delay and calculate the amplitude of the detected signal for many different configurations. The analysis of the simulation results requires the manual adjustment of the data analysis parameters, as the filter cutoff frequency or the signal delay. Using the principle that a slow varying group delay has a minimum standard deviation if it is well filtered, we developed an automatized version of the the 1/Q detection, designed as IQA method. With this technique, it was possible sweeping the probing angle at all the positions in an acceptable time and select the optimized configuration. The maximum average detected amplitude shown to be a good selection criteria for the optimized configuration. The results show that, with the exception of some positions in the divertor region, there is an optimized configuration with low position error {<1 cm) and the power losses minimized.With the optimized configuration, the stability of the system was tested for plasma displacements of 5 (reference case) and 15 cm (limit case). The results show that, in contrast to the results of the configuration with the antennas perpendicular to the separatrix, the system is stable for 5 cm plasma displacements in different directions (0, 90, 180 and 270 degrees). For displacements of 15 cm, the positions at the top of the machine can reach errors in the order of the minimum error requirement (1 cm).The effect of turbulence in reflectometry measurements was studied in one gap of the equatorial region, in the high field side. Due to the lack of information on the turbulence properties of DEMO plasmas, the fluctuations were defined with an analytical model. A Kolmogorov-like spectrum was used to generate 400 random plasma samples for 16 different levels of amplitude (1-16%), compatible with the order of values observed in the experiments. Using the IQA algorithm, the principal statistical parameters were calculated. The results show that for higher levels of turbulence ($>5%$), the mean position error becomes negative due to the change of the effective cutoff position. This effect occurs for all the frequencies, leading to an accumulative error that can affect the position measurement in the order of accuracy requirements. In order to prove the reliability of the entire system, it is necessary to apply the same procedure to the other positions of the system, which requires a huge amount of computation time on HPCs to be done.The techniques and the algorithms developed in this work can be applied in other processes which involve the analysis of a high number of reflectometry simulations, including studies with other reflectometry techniques.

Minimal Solutions to the CKM Unitarity Problem with a Vector-like Quark Isosinglet
2022-02-03 12:00 - 14:00 | Online
Abstract:Cálculos e resultados recentes apresentam fortes evidências de que a matriz CKM não é unitária, contradizendo o MP e sugerindo a existência de Nova Física (NF). Nesta tese, propomos uma extensão mínima do Modelo Padrão (MP) com um quark vector-like do tipo up, que fornece uma solução simples para o problema da unitaridade da matriz CKM (CKM-UP).Adotamos a parametrização Botella-Chau para a matriz de mistura , usando os três ângulos e fase habituais da matriz do MP, mais três ângulos extra e duas novas fases. São obtidas características interessantes e um novo padrão de decaimentos do , predominantemente para a primeira geração. Averiguou-se também se os limites pelos Electroweak Precision Measurements (EWPM) são excedidos.

Dark matter in three-Higgs-doublet models with S3 symmetry
2022-02-09 16:15 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Models with two or more scalar doublets with discrete or global symmetries can have vacua with vanishing vacuum expectation values in the bases where symmetries are imposed. If a suitable symmetry stabilises such vacua, these models may lead to interesting dark matter candidates, provided that the symmetry prevents couplings among the dark matter candidates and the fermions. We analyse three-Higgs-doublet models with an underlying S3 symmetry and discuss all possible vacua.Two models, with and without CP violation, are explored in detail. In our framework the stability of the dark matter sector results from a Z2 symmetry which survives the spontaneous symmetry breakdown of the initial S3 symmetry. One of the doublets provides the DM sector, while the other two are active.

Old and new ideas about the flavour structures of quarks and leptons
2022-02-16 16:15 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Meeting ID: 849 8854 1912Meeting password: [REDACTED] Abstract:Several theoretical and experimental problems require that the Standard Model of particle physics is extended. The fact that three generations of quarks and leptons exist is not understood, but it does not belong to this list of problems. The fermion masses and mixings show, however, apparent regularities and hierarchies which suggest that it could be related to and understood by new physics. The talk will cover some existing ideas how the flavour structures might emerge and it will cover recent work which maps the structures onto new parameters which may be easier to explain.

Peeling in Generalized Harmonic Gauge
2022-02-17 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Starting from a generalization of the good-bad-ugly model, we showed that the solutions to the Einstein field equations in generalized harmonic gauge (GHG) admit polyhomogeneous expansions near null infinity. This allows us to find out, under a very general class of initial data, whether the peeling property holds for each gauge choice. In general, we find that it does not. However we find that the interplay between gauge and constraint addition can be exploited in order to recover peeling. The same method can be used to build a regularization of the Einstein field equations in GHG.

Discovering Lepton Flavour Universality Violating New Physics
2022-02-23 16:15 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: Hints for the violation of lepton flavour universality (satisfied within the SM) have accumulated in recent years. In particular, deviations from the SM predictions were observed in semi-leptonic B decays (b->sll and b->ctau), in the anomalous magnetic moment of the muon (g-2), in leptonic tau decays and di-electron searches. Furthermore, also the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly, can be interpreted as a sign of lepton flavour universality violation. In this talk I review the status of these anomalies and give an overview of the possible interpretations in terms of new physics models.

Torsion bigravity: a purely geometric modified theory of gravity
2022-02-24 14:30 - 16:00
ABSTRACT: I will present torsion bigravity, which is a theory of dynamical massive spin-2 field of geometrical origin (dynamical torsion field). I will cover various issues as: - motivation and theoretical basement of this type of modified gravity; - the torsion bigravity world: known solutions and their physical properties, phenomenological consequences. In particular, I will discuss some consequences for the black hole physics.

Extreme particle acceleration in astrophysical plasmas: from simulations to observations via laboratory experiments
2022-03-02 16:00 - 18:00 | PA1, Pavilhão de Matemática
Abstract:Astrophysical plasmas are extraordinary particle accelerators, from supernova remnants to the relativistic jets that emanate from supermassive black holes and produce very-high-energy cosmic rays and shine across the electromagnetic spectrum. The mechanisms behind these cosmic accelerators remain a long-standing mystery. They are thought to be associated with basic plasma processes, including collisionless shocks and magnetic reconnection, that control energy dissipation in these systems. These processes involve a complex and nonlinear interplay between the dynamics of flows, magnetic fields, and nonthermal particles that is not yet well understood and affects the observational manifestations of the astrophysical environments. I will discuss how the fast progress in computational and experimental capabilities is creating unique opportunities to push the boundaries of our understanding of the dominant particle acceleration mechanisms by allowing detailed kinetic modeling of different plasma processes and controlled laboratory experiments that can help validate these models.Short Bio:Frederico Fiuza is a Senior Staff Scientist and the Theory Group Leader at the High Energy Density Science division at the SLAC National Accelerator Laboratory. He obtained his PhD degree in Plasma Physics from Instituto Superior Tecnico, Portugal, in 2012. He then became a Lawrence Postdoctoral Fellow at the Lawrence Livermore National Laboratory between 2012 and 2015, before joining SLAC. His research interests span a wide range of topics in astrophysical and laboratory plasmas, including particle acceleration, magnetic field amplification, collisionless shocks, and magnetic reconnection. Recently, Fiuza's work on laboratory astrophysics was recognized with the 2018 APS Thomas H. Stix Award for Outstanding Early Career Contributions to Plasma Physics Research and the 2020 APS John Dawson Award for Excellence in Plasma Physics Research. He has also been awarded the Lawrence Fellowship in 2012, the European Physical Society PhD Research Award in 2013, and the DOE Early Career Research Program Award in 2017.

Aspects of nonlocally modified gravity and of cosmological numerical relativity
2022-03-03 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:As I am a new postdoc fellow at CENTRA, I propose to summarise my previous and current main works, and briefly describe associated future perspectives. This will consist of the discussion of two distinct bodies of work, one of them lying in modified gravity (dark energy) and the other one in numerical relativity applied to cosmology. First, I will outline field theoretical aspects as well as observational constraints and Bayesian model selection studies of a particular class of modified gravity theories, so-called nonlocal gravity theories. In particular, I will review the relevant phenomenology of selected nonlocal models in the light of different cosmological probes such as the cosmic microwave background, supernovae, large scale structure, but also future gravitational waves interferometers. In a second part, I will describe my research in numerical relativity that constitutes an attempt towards the development of a fully general relativistic N-body code for cosmological structure formation.

Dark matter searches at future e+e- linear colliders
2022-03-03 16:15 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The future linear e+e- colliders offer a number of unique opportunities for searches for dark matter and dark sector particles. The collider program itself will offer important capabilities on three frontiers: (i) the precision frontier with measurements at the Higgs factory, (ii) the energy frontier with direct investigations of the scalar sector, and (iii) the intensity frontier with fixed-target and beam-dump measurements. In the seminar I will concentrate mostly on (ii) but also comment on possible experiments in (i) and (iii), which altogether address various dark sector portals.

Nonlocality and Contextuality: Concepts and Applications in Quantum Information
2022-03-04 09:30 - 11:00 | Online
AbstractIn quantum foundations and quantum information, understanding the notion of non-cfc.ss/enfi/y is of extreme importance. This term broadly characterizes quantum phenomena which not only appear to be at odds with certain instances of classical intuition, but are provably in contradiction with empirical predic- tions of classical theories. The archetypal examples of non-classical phenomena, produced by operational quantum mechanics, are nonlocality and contextuality, which have traditionally been characterized within a framework of impossibility results, known as no-go results. Nonlocality and contextuality, while being at the core of the weirdness and conceptual issues of quantum theory, also provide useful information theoretical resources that can be harnessed for information processing purposes, for instance, in quantum computation and quantum cryp- tography. In this thesis, we detail various types of non-classical phenomena, in particular nonlocality and contextuality, by studying them within the framework of cooperation multiplayer games. This framework provides an intuitive way to interpret such no-po results as interactive protocols where agents try to jointly compute a desired function under a set of operational restrictions. Therein, the non-classical behaviour particular to the setup emerges as a resource for appropriately constructed games, powering the so called gunntutn-over-cla.ssiral advantage — a term which succinctly describes that players exploiting the full range of operational quantum strategies perform better at the game than the players restricted to the alternative classical theories. Finally, we will discuss some applications in quantum information, namely, within quantum cryptogra- phy, where different types of non-classical behaviour are of crucial importance in order to guarantee security of various protocols.

Development of a portable magnetic flow cytometer for the detection of hospital bacterial infections
2022-03-07 10:00 - 12:00 | Online
AbstractThe rising incidence of infectious diseases, increased food and water safety concerns, and the new government initiatives and funding to detect and control antimicrobial-resistant species are demanding breakthrough advancements in bioanalytical tools for pathogen detection. Moreover, the clinical prevalence of Pseudomonas aeruginosa, and Klebsiel/a pneumoniae pathogens underscores the importance of rapid detection approaches to contain nosocomial infections and reduce the development of drug resistance. Current microbiological detection systems often lack precision, affordability, and portability. Furthermore, they require long detection times, sophisticated infrastructures, and trained personnel, which prevent their applicability at resource-limited settings.In this thesis work, some of these challenges were addressed by developing a magnetic flow cytometer technology. Flow cytometers have become essential instruments in biomedical research and routine clinical tests for disease diagnosis , prognosis, and treatment monitoring. Magnetic flow cytometers ally the potential for cell detection and counting to the advantages of a lab-on-a-chip technology, pushing forward the progress in integrated and compact systems for On-site testing. In particul ar, magnetoresistive sensors (MR) and magnetic labelling processes were exploited, promoting high capture efficiencies of magnetically labelled targets and generating strong magnetic fields .The MR chip was integrated with a microfluidic system with a small heigh dimension to improve the system sensitivity by promoting the labeled targets to be closer to the sensing units. Chip design optimizations regarding the maximization of the sensor sensitivity and reduction of electromagnetic interferences, as well as improving the processing signal analysis and boosting multiplex capabilities were perfo rmed .Protocols for the functionalization of bacteriophages and antibodies onto the magnetic nanoparticles surfaces were optimized and validated for the magnetic labelling of bacterial cells (K pneumoniae and P aeruginosa) spiked in buffer solution, as well as, directly from clinical rectal swa bs. The results showed capture efficiencies over 70 % with specificity.The whole system was integrated with an electronic acquisition setup for the sensors addressing and read-out in collaboration with INESC ID. A signal classificationmethod based on simulations was proposed to aid in the identification of the number of magnetically labelled bacteria associated with each detection event, as well as in the ability to distinguish signatures of free or clustered magnetic particles from magnetically labelled targets.This platform was tested and validated for the detection of K/ebsie//a pneumonia in laboratory samples as well as a pilot study was conducted with clinical rectal swab samples collected from 45 patients admitted to the emergency department of Hospital Beatriz Angelo (Loures, Portugal).Overall, this work mostly outlies relevant aspects concerning biosensor development, demonstrating how magnetic flow cytometry can be explored as an accurate, sensitive, and portable device that can be applied for bacteria detection and identification.

From quarks and gluons to hadrons and multiquarks
2022-03-08 16:00 - 18:00 | Online

FlexibleDecay: An automated calculator of scalar decay widths
2022-03-09 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:I will present FlexibleDecay, a tool to calculate decays of scalars in an arbitrary BSM model. The tool aims for high precision particularly in the case of Higgs boson decays. In the case of scalar and pseudoscalar Higgs boson decays the known higher order SM QED, QCD and EW effects are taken into account where possible. The program works in a modified MSbar scheme that exhibits a decoupling property with respect to heavy BSM physics, with BSM parameters themselves treated in the MSbar/DRbar-scheme allowing for an easy connection to high scale tests for, e.g., perturbativity and vacuum stability, and the many observable calculations readily available in MSbar/DRbar programs. Pure BSM effects are taken into account at the leading order, including all one-loop contributions to loop-induced processes. The program is implemented as an extension to FlexibleSUSY, which determines the mass spectrum for arbitrary BSM models, and does not require any extra configuration from the user.

Plasma dynamics in extreme fields: challenges and opportunities
2022-03-09 16:00 - 18:00 | PA1, Pavilhão de Matemática
Title: Plasma dynamics in extreme fields: challenges and opportunitiesAbstract: The next generation of lasers will access intensities above 10^23 W/cm^2. When plasmas or relativistic electron beams interact with these lasers, energy loss due to radiation emission, or quantum effects such as electron-positron pair creation become important for their dynamics. Repeated occurrence of pair creation can induce a so-called “QED cascade”, that generates an exponentially rising number of particles. This allows for creating exotic plasmas that are a mix of electrons, ions, positrons, energetic photons and intense background fields. Extreme laser-plasma interactions can be explored to form optical traps, create&accelerate particles and produce novel radiation sources. I will introduce a QED module coupled with the particle-in-cell framework OSIRIS that allows studying nonlinear plasma dynamics in the transition from the classical to the quantum-dominated regime of interaction. Studies relevant for (near) future experiments will be discussed.Short Bio: Marija Vranic obtained her MSc degree from University of Belgrade, Serbia and her PhD at Instituto Superior Tecnico in Lisbon, Portugal. After PhD, she was working in Extreme Light Infrustructure in Prague, Czech Republic, and then returned to Portugal. Her research is focused on plasmas in extreme conditions, where quantum effects can affect the collective plasma dynamics. She combines analytical theory and massively parallel computer simulations to perform the studies relevant for state-of-the-art and near-future laser experiments using the most intense lasers in the world. Marija is a winner of the international John Dawson PhD thesis prize (best PhD thesis worldwide in the field of plasma-based accelerators) and the IBM Scientific Prize. As a PI, she was awarded 250k€ R&D grant by FCT and several international supercomputing grants (a combined > 200 milion CPUh).

Gravitational waves from primordial fluctuations
2022-03-10 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The evolution of primordial fluctuations in the early universe is accompanied by a production of gravitational waves. The so-called induced gravitational waves are the cosmic messenger of primordial fluctuations on the smallest scales, which may have been generated during cosmic inflation. In this talk, I will discuss how they may be used to explore the early universe's initial conditions and expansion history. This includes gravitational waves induced by oscillatory features in the primordial spectrum, early isocurvature fluctuations and a primordial black hole dominated universe.

Asymmetric Quantum Cryptography and Multipartite Correlations
2022-03-16 15:00 - 17:00 | Online
AbstractThe subject of this thesis is the analysis of secure asymmetric cryptographic schemes, and the study of the main resource for information processing protocols, the total, classical and quantum multipartite correlations.Motivated by the usefulness of secure multiparty computation as a privacy-protecting data analysis tool, we proposed a practical quantum realization of randomized oblivious transfer. Our solution is aimed at targeting the limitations of security and efficiency faced by the classical schemes for oblivious transfer. A detailed security proof was written for the protocol. We also provide preliminary results of performance from an experimental setup based on an entangled photons source and polarization encoding.The impossibility results for achieving unconditionally secure bit commitment have driven the research for secure solutions under several different assumptions. We propose a criteria for ranking the complexity of such assumptions, together with new functionality, called the asymmetric quantum beamer, which is minimal under the listed criteria. Using this new assumption we develop a universally composable bit commitment protocol with linear com plexity in its security parameter.Based on previous work for a correlation hierarchy for probability distributions, we for malize a framework of correlation structures for quantum systems. We explore some of its mathematical properties, computational complexity, use for information compression of quantum states, and some aspects of categorization of correlations by the way they are dis tributed as well as by their nature (classical/quantum). Additionally, we present a practical application for the correlation structures framework for early classification of time series data sets. The proposed method is based on selectively cutting correlations that are not directly connected to the class variable until a criterion of optimality is satisfied. The algorithm was able to successfully guess the class of test data from real world sources using only a few initial time steps. Its versatility for application for other problems is highlighted.Finally, we lay the foundations of a quantum algorithmic complexity theory based on the dc-QTM model. We conclude that, although the algorithmic complexity of a physical state and its classical description are equivalent, they can be differentiated while taking the role of a resource to compute another state. Additionally, we prove that the chain rule does not hold for this version of algorithmic complexity and argue how that result can be used to define the complexity of correlations in quantum systems.

Applications of black hole scattering
2022-03-17 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:In this talk, I will describe scattering in the presence of black holes. I will try to convince you thati) there is a new regime in the phase space of quantum gravity where scattering amplitudes can reliably be calculated in the low energy theory,ii) Hawking's free field theory breaks down after Page time (implying information retrieval in local effective field theory), and thatiii) there is an emergent soft limit near the horizon, resulting in new soft graviton theorems in the presence of black holes.Finally, I will conclude with some more applications.

Symmetries of Gravity: from the Early Universe to Black Holes
2022-03-23 16:00 - 18:00 | PA1, Pavilhão de Matemática
Symmetries are at the core of our understanding and description of most physical phenomena across all accessible energy scales, from the organization of the structures at the largest distances in the Universe to the physics governing the fundamental interactions of subatomic particles. The focus of my talk will be on gravitational theories. I will show examples of Goldstone bosons in cosmology and discuss the role of non-linearly realized symmetries of gravity. I will then present recent developments in the context of symmetries of black holes and their relevance for gravitational-wave astronomy.Bio: I obtained my Ph.D. from Scuola Normale Superiore, Pisa, in 2016. I was then a postdoctoral research scientist first at Utrecht University and later at Columbia University. I am currently a research fellow at the International Centre for Theoretical Physics (ICTP) in Trieste. My primary research interests and my main original scientific contributions are in the context of effective field theories, theoretical cosmology and black holes.

Hidden Symmetries of Gravity
2022-03-24 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:I will discuss classes of hidden symmetries of gravity and their consequences for black holes and compact objects. It is well known that asymptotically flat black holes in general relativity have a vanishing static tidal response (i.e., zero Love numbers). In the talk, I will first show that this is the result of a hidden structure of ladder symmetries governing static (spin 0,1,2) perturbations around black holes, and I will discuss the underlying geometric origin. I will also present examples of hidden symmetries and dualities at finite frequency and their consequences for quasinormal modes. I will finally briefly present an effective field theory for perturbations around black holes in scalar-tensor theories and discuss how to connect the effective couplings to possible deviations in the observed ringdown frequencies.

From quarks and gluons to exotic hadrons
2022-03-30 16:00 - 18:00 | PA1, Pavilhão de Matemática
Abstract:With recent experimental evidence for tetraquarks and pentaquarks, hadron spectroscopy is nowadays a cutting-edge area of research with the LHC among its central facilities. Hadrons are bound states of quarks and gluons in QCD, the theory of the strong interaction, but their spectrum and structure are much richer than the naïve quark model suggests and governed by nonperturbative phenomena such as confinement and dynamical mass generation.In this colloquium I will make a survey through some open questions in QCD, with an emphasis on the structure of exotic hadrons and multiquarks, and connect them with the key underlying phenomena of mass generation for quarks and gluons. I will highlight recent advances with functional methods, which allow one to compute hadron properties from first principles. Systematic improvements in this approach have made it possible to address a wide range of problems from multiquark spectroscopy to form factors, parton distributions, the anomalous magnetic moment of the muon, and the QCD phase diagram.Short Bio:My research is centered around nonperturbative phenomena in QCD and nuclear and hadron physics, including hadron and multiquark spectroscopy and structure, Compton scattering and the muon g-2 problem. I obtained my PhD degree at the University of Graz (Austria) and carried out research stays at Argonne National Laboratory (USA), TU Darmstadt, and the University of Giessen (Germany). In 2017 I moved to IST Lisboa within an FCT Investigator Grant, and in 2020 our group NPStrong joined LIP.

Searching for Habitable Worlds: Challenges & Opportunities
2022-04-06 16:00 - 18:00 | PA1, Pavilhão de Matemática
Title: Searching for Habitable Worlds: Challenges & OpportunitiesSpeaker: Prof. Lisa Kaltenegger, Director of the Carl Sagan Institute at Cornell University, NY, USAAbstract: More than 5000 detected extrasolar planets have shown us the huge diversity of these new worlds: among the surprising discoveries are hot planets orbiting their star in only a few hours, lava worlds, Mini-Neptunes as well as the first potential rocky worlds in the temperate Habitable Zone of their host stars.Observation techniques have already reached the sensitivity to explore the chemical composition of the atmospheres of some hot exoplanets. With the successful launch of the James Webb Space Telescope, we will be able to glimpse into the atmosphere of potentially habitable worlds orbiting other stars.For now, our own planet is our only key to spot life in the universe. Its evolution through time and its diverse biota give us clues on what to search for. The spectra of planets are our window to explore potential habitable worlds lightyears away - as well as to understand our own planet better. This talk will present the newest results in our search, its challenges and opportunities on the way to finding out whether or not we are alone in the cosmos.

Testing the nature of dark compact objects and dark matter with gravitational waves
2022-04-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The direct observation of gravitational waves already allowed us to directly observe hundreds of dark ultracompact objects (most likely black holes) that were entirely invisible to us until very recently. As remarkable as this feat already is, these observations only mark the beginning of what lays ahead. Planned future gravitational-wave detectors promise to make gravitational-wave physics a precision, data-driven science field, which will make it possible to address (and possibly open new) outstanding problems in various areas of physics and astronomy but also potentially opening the door to unexpected discoveries.With this motivation in mind, in this talk I propose to summarise some of my past and current work that aims at tackling questions such as: how well do the black hole solutions predicted by General Relativity explain the dark compact objects we observe with gravitational waves? Are there other more exotic compact objects in the Universe? Is dark matter composed of particles, such as axions or dark photons? In particular, I will (i) discuss how the multipolar structure of compact objects can be inferred through gravitational wave observations, focusing on recent work where we computed the corrections to the dynamics of a binary system due to generic, nonaxisymmetric mass quadrupole moments to leading post-Newtonian order and (ii) (time permitting) shortly discuss current and future prospects for gravitational-wave observations to directly constrain the existence of ultralight boson fields, which have been proposed as strong dark matter candidates.

Novel microelectrode array architectures for high precision activity recordings of 3D in vitro neuronal populations
2022-04-19 16:30 - 18:30 | Online
Sumário:Brain research is now resorting to nanotechnology in order to create efficient devices for neuronal recording. Typical extracellular microelectrodes present sub-optimal electrical coupling between neurons and electrodes. The goal of this work is to present novel 3D architectures to maximize the interaction between electrodes and the neuronal network, and to demonstrate the viability of 3D in-depth neural recordings, providing a major breakthrough in the field. To this end, an electrical model of the neuron-electron coupling is to be developed and simulated, followed by the elaboration and implementation of a protocol for 3D electrode micro/nanofabrication. The demonstration of the fabricated device will be performed by growing a neuronal culture on the array and acquiring electrical measurements. The outcome of this project will enable neuronal data acquisition in 3D networks, greatly benefitting the study of neuronal systems and advancing our understanding of neuronal functional diseases.

Problems in the Foundations of Physics
2022-04-20 16:00 - 17:00 | Online, zoom
Title: Problems in the Foundations of PhysicsAbstract: In the foundations of physics, we have long-standing open problems such as the nature of dark matter and dark energy, the hierarchy problem, or the missing quantization of gravity. Yet physicists have not made progress on solving those problems for 50 years. In this talk, I discuss how physicists ended up in a vicious cycle of theorizing and null results, and what we can do to overcome the present phase of stagnation.

Black holes in grand canonical ensemble
2022-04-21 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: From the successful works of Bekenstein and Hawking, it is known that black holes are thermodynamic objects. In particular, black holes emit particles as a black body at the Hawking temperature, and have a precise entropy, the Bekenstein-Hawking entropy. The nature of the entropy of a black hole is still an open problem, a possible explanation may lie on a theory of quantum gravity. In this seminar, I will talk about the construction of the canonical and grand canonical ensemble for black hole spacetimes using the path integral approach to quantum gravity. Such ensembles determine the thermodynamics of a black hole from a semiclassical approximation of the quantum theory. The seminar is planned as follows: (i) I will summarize previous works, from Gibbons and Hawking, to York and André and Lemos; (ii) I will then describe the results of my current work on the grand canonical ensemble of d-dimensional ReissnerNordström black holes in a cavity and compare them to the case of a charged conducting sphere in flat d-dimensional spacetime in a cavity.

Fink broker, an optimized recommendation system for transient follow-up
2022-04-22 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Next generation experiments such as the Vera Rubin Observatory Legacy Survey of Space and Time (LSST) will provide an unprecedented volume of time-domain data opening a new era of big data in astronomy. To fully harness the power of these surveys, we require analysis methods capable of dealing with large data volumes that can identify promising transients within minutes for follow-up coordination. In this talk I will describe the infrastructure put in place by LSST to handle approximately 10 million transient candidates per night and present Fink, a broker developed to face these challenges. Fink is based on high-end technology and designed for fast and efficient analysis of big flows. It has been chosen as one of the official LSST brokers and will receive the full data stream. I will highlight the state-of-the-art machine learning techniques used to generate early classification scores for a variety of time-domain phenomena including kilonovae and supernovae, as well as for artifacts, like satellites glitches. Such methods include Deep Learning advances and Active Learning approaches to coherently incorporate available information, delivering increasingly more accurate added values throughout the duration of the survey. I will also highlight the potential for discovery of new categories of sources and how we can optimize for discovery in the era of LSST.

Towards the detection of ultra-low energetic neutrinos with plasma metamaterials
2022-04-26 14:00 - 16:00 | Online
AbstractTheoretical works showed the existence of neutrino flux with energy below eV, the detection of these low energetic neutrino can shed light on Dark Matter problem along with the improvement of the Standard Model; the detector used nowadays are not able to detect such energies, in this thesis we propose a technique to detect slow flux of massive neutrino by plasmon generation. Through the semiclassical approximation of the Weak Interaction, we derived the force felt by a plasma due to the neutrino distribution, and vice-versa; therefore, by the Kinetic description with linear perturbation approach, we studied the interaction of electron plasma and neutrino flux. The long lifetime of plasmon in graphene structures oriented us to study bidimensional (2D) electron systems; the Weak interaction, between neutrino and ungated electron solid-state plasma, leads to a feature alike the beam-plasma instability, raising the possibility to have a growth rate. The generated plasmon has Wavevector dependent on the neutrino velocity and spectral width function of the neutrino’s density and mass; the instability was considered in an effective tridimensional (3D) metamaterial obtained by graphene heterostructure, the resulting Signal to Noise ratio (SN) is mainly dependent on the length of the device. Larger growth rates are found for lower neutrino energy and larger density: with detector size in the order of centimeters, the detection of neutrino with energy µeV is ensured for flux above 105 cm−2 with SN about 10 dB, for meV neutrino the same SN is ensured for flux above 1012 cm−2 .

Black Holes and Dark Matter
2022-05-05 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The discovery of gravitational wave signals from merger events of massive binary-black-hole (BBH) systems have prompted a renewed debate in the scientific community about the interplay between Black Hole phenomenology and Dark Matter searches. On the one hand, Black Holes of primordial origin (PBHs) may have formed in the early Universe and could constitute a significant portion of the elusive dark matter that, according to standard cosmology, makes up the majority of the matter content in the universe. On the other hand, peculiar classes of Black Holes can be studied as "portals" to Dark Matter detection in the Gravitational Wave channel, due to the large density of DM that is expected to be present around them. In the first part of the talk, I will review the most promising multi-messenger avenues towards detection of PBHs. I will first focus on the radio/X-ray band, and present the prospects of discovery for both a hypothetical PBH population and the guaranteed population of astrophysical isolated black holes in our Galaxy, based on the broad-band emission from the interstellar gas that is being accreted onto them. Then, I will turn my attention to the gravitational wave domain, and discuss the merger rate of black-hole binaries. I will present a detailed evaluation of the expected rate from a generic (subdominant) component of PBHs, and analyze the role of future observation at high redshift to identify a primordial component on top of the rate associated to astrophysical BHs. In the final part of my talk, I will turn my attention to the impact of Dark Matter overdensities around Intermediate-Mass Black Holes, and on their impact on the gravitational waveform emitted in presence of an Intermediate-Mass-Ratio inspiral. I will demonstrate that the dephasing effect induced by the presence of the DM is observable in this channel, and the properties of the DM overdensity can be measured by the upcoming LISA observatory.

Searching for scalar dark matter using spectroscopy
2022-05-05 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:A possible implication of a sub-eV scalar dark matter (DM) field interacting with the Standard Model (SM) is oscillations of fundamental constants. Here, I will talk about how to establish the direct experimental bounds on the coupling of an oscillating DM to the SM using spectroscopy and/or various quantum sensors (DDM search). The equivalence principle (EP) violating tests can also be used to constrain the existence of a light scalar. Furthermore, I will discuss about the complementarity between the EP violating tests and DDM searches. We will further explore the challenges of a quadratically coupled light DM in the context of naturalness and how to probe such models.

Quasi-Disorder Effects in Topological Superconductors
2022-05-09 15:15 - 17:30 | Sala P3 Pavilhão de Matemática, Piso 1/ Online
Resumo:Estudamos os efeitos da desordem de Aubry-André e desordem de Anderson para um modelo de um supercondutor topológico bidimensional com um campo magnético externo. São estudados os casos de um supercondutor de emparelhamento tipo p e um supercondutor não centrossimétrico com mistura de emparelhamentos de tipo p e s e com acoplamento spin-órbita de Rashba. Revemos as propriedades topológicas do sistema sem desordem, que dependem da direção do campo magnético (perpendicular ou paralelo ao plano do supercondutor). O sistema desordenado é estudado tanto no espaço real como num espaço misto.Quando o campo magnético é paralelo, estudamos os efeitos de quasi-desordem e desordem, aplicada tanto nas fronteiras como no interior do supercondutor, e discutimos os seus efeitos na localização do sistema, densidade de estados e nas funções de onda, numa abordagem no espaço real. Ainda no espaço real mostramos que, para um campo magnético perpendicular, a introdução de quasi-desordem leva ao aparecimento de novas regiões topológicas, caracterizadas por um valor inteiro do número de Chern.Numa abordagem no espaço misto, identificamos novos regimes com o aparecimento de novas bandas planas de Majorana e também novos estados de fronteira de Majorana unidirecionais, com a introdução de quasi-desordem. Mostramos que as bandas planas de Majorana têm uma fase Berry quantizada de π e indentificamo-la como um invariante topológico. Duas transições topológicas são identificadas e os valores dos expoentes críticos z e ν são obtidos. A natureza fractal dos estados é discutida tanto para desordem de Anderson como para desordem de Aubry-André.

Quantum Horizons and the Emergence of Gravity and Space-Time
2022-05-11 16:00 - 18:00 | PA1, Pavilhão de Matemática
Abstract: Event horizons may occur near black holes, in flat space or in a cosmological spacetimes. In the last decade important progress has been in the understanding of the quantum properties of the horizons. These advances have revealed a deep connection between thermodynamics, quantum entanglement, and the emergence of the laws of gravitation.Even the fabric of spacetime itself has to be viewed as being emergent from a microscopic quantum mechanical description. In this colloquium I will review these developments and explain the recent insights on the black hole information paradox.Subsequently I will discuss the generalization and implications of these ideas to flat space and cosmological spacetimes. I will end with a discussion of possible observational consequences.

Analogue Binaries and Superradiance
2022-05-12 11:00 - 13:00 | Anfiteatro PA1, piso -1, Pavilhão de Matemática
Resumo: A natureza difusa de matéria bosónica ultraleve e o seu fraco acoplamento ao modelo standard torna o seu estudo possível quase exclusivamente através dos seus efeitos gravitacionais.A descoberta do fenómeno da Superradiância em torno de buracos negros faz deles os laboratórios ideais para estudar as propriedades destes possíveis constituintes da Matéria negra.O fenómeno da superradiância, análogo ao famoso processo de Penrose para ondas, permite que campos escalares extraiam energia rotacional de buracos negros, abrandando a sua rotação, e assim deixando marcas observacionais claras que permitem colocar limites na massa de tais campos.A superradiância em torno buracos negros tem vindo a ser alvo de extensos estudos na última década. Contrasta esse com o estudo de campos escalares em sistemas binários de buracos negros, onde o nosso conhecimento fica ainda a desejar. O crescente número de detecções de ondas gravitacionais provenientes de sistemas binários de objectos compactos e o desenvolvimento da nova geração de detectores torna imprescindível perceber como podem estes campos escalares moldar evolução e dinâmica de tais sistemas.Ao preservar as principais características de tais sistemas astrofísicos, o estudo de modelos-análogos oferece-nos uma via para melhor entender a sua dinâmica. Através de resultados quantitativos e qualitativos o estudo de tais modelos permite também perceber como novos dados experimentais podem ser utilizados para entender a natureza e desvendar as propriedades destes campos.

The Milky Way mass function as a probe of dark matter models
2022-05-12 14:30 - 16:00 | Sala de Reuniões (2-8.3) Pavilhão de Física
ABSTRACT: Predictions for the properties of the Milky Way (MW) satellite galaxies are crucial tests for competing dark matter models. Deviations from the cold and collisionless picture of dark matter, such as free-streaming, dark acoustic oscillations, and self-interactions between dark matter particles, modify predictions for the number of MW satellite galaxies and/or for their densities. Calculating accurate predictions is complicated by the large array of factors relevant to satellite formation and processing, including the stochasticity of MW halo formation, the difficulties in modelling satellite stripping with limited resolution, and for contraction of the host halo through cooling baryons, to name but a few. In this talk I will use the COCO N-body simulations of MWanalogue systems to make estimates for the MW satellite population properties in three models: cold dark matter (CDM), a warm dark matter model (WDM) with a thermal relic mass of 3.3keV, and a self-interacting dark matter model (SIDM) that enables gravothermal collapse. I will use these models to predict the range of viable subhalo hosts for ~33 observed MW satellites, and then discuss how future observations will enable us to ascertain which model best describes the properties of dark matter.

The Science of Climate Change
2022-05-18 16:00 - 18:00 | PA1, Pavilhão de Matemática
Abstract: A brief historical perspective of climate change science since the publication of Joseph Fourier's papers on the greenhouse effect up to the development of General Circulation Models and the more accurate prediction of climate change as a result of anthropogenic emissions of greenhouse gases by Syukuro Manabe and Klaus Hasselmann and the connection of their work to Giorgio Parisi's contributions to the theory of disordered materials and random processes, will be presented. The present world situation as regards climate change and its future evolution will be discussed. Finally an overview of the main climate change impacts now and in the future in Europe and in Portugal will be presented.

Explosive transients, their origins and their use to study the high-redshift Universe
2022-05-19 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Explosive transients are usually connected to massive stars, directly or indirectly. Some of the most luminous of those explosions are gamma-ray bursts (GRBs) and superluminous supernovae (SLSNe). GRBs come in two different classes, long GRBs whose progenitors are massive stars with low metallicity and high rotation rate, and short GRBs, the merger of two compact objects and one of the known sources of gravitational wave signals. Type I SLSNe (without H in their spectra) were first thought to have progenitors similar to long GRBs, but studies of the host galaxies have suggested more extreme stars for those events. Due to their rare numbers and the fact that they are hosted mostly in dwarf galaxies we will likely not be able to observe the progenitor systems of any of these events before explosion in the near future. In this talk I will review what we know about the progenitors of different stellar explosions and how we use the host galaxy and environment to get indirect information on the progenitor, in particular using 3D spectroscopy. One important aspect is where the star-formation originates giving rise to the progenitors and I will focus on a peculiar, nearby, host galaxy where we have multi-wavelength data to study possible star-formation processes. I will also present how we can use in particular GRBs to study the ISM in high-redshift galaxies with absorption lines in the afterglow spectrum and present the first metallicity measurement of a short GRB host. Finally, I will review how and if we might be able to use these explosions to test the expansion of the Universe.

Advanced Plasma Physics Goals, Syllabus, and Methodology
2022-05-24 10:00 - 12:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)

The Higgs-Gravity Connection
2022-05-25 16:00 - 18:00 | PA1, Pavilhão de Matemática
Abstract:The geometrical formulation of gravity emerges naturally from the equivalence principle, hinting toward an intriguing connection with the concepts of mass and inertia. As already observed by Einstein, General Relativity can be expressed in a variety of ways, including not only the most common metric approach but also the Palatini, teleparallel, and Einstein-Cartan formulations. These realizations differ mainly in their choice of fundamental degrees of freedom, being otherwise mathematically equivalent as pure gravity is concerned. The degeneracy among different gravity incarnations breaks down, however, in the presence of non-minimal couplings to matter, as happens unavoidably when accounting for the Standard Model Higgs. This opens the possibility of testing the nature of gravity with cosmological observations. In this talk, I will provide an overview of this fascinating paradigm, describing its predictions, generalizations, open questions, and implications for the infamous hierarchy problem.

Improving the signal-to-noise ratio in Lattice QCD
2022-05-26 11:00 - 13:00 | Online
Abstract: Spectra with full towers of levels are expected due to the quantization of the string vibrations, however different theoretical models exist for the excitation spectra. First principle computations are important to test the different models and to search for novel phenomena, but so far only a few excited states of QCD flux tubes have been studied with pure gauge SU(3) lattice QCD in 3+1 dimensions. We thus aim to study a spectrum of flux tubes with static quark and antiquark sources up to a significant number of excitations. In this thesis, we compute the excitation of the flux tube for quantum numbers Λ η =Σ+ g ,Σ− g , Σ+ u , Σ− u , Πg,Πu, ∆g, ∆u, where for some of them just the ground state or up to two levels were calculated and published in the literature. To achieve the highest possible excitation level, we construct a large set of operators with the correct symmetry, solve the generalized eigenvalue problem and compare the results of different lattice QCD gauge actions with different lattice spacings and anisotropies.

The predictive power of numerical relativity
2022-05-26 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Numerical relativity plays many important roles in astrophysics andgeneral relativity. For example, it plays an important role inconstructing theoretical templates of gravitational waves which arecrucial for detecting gravitational waves and extracting the physicalparameters of gravitational-wave sources. In this talk, I will introduceour latest numerical-relativity simulations for neutron-star mergerspaying particular attention to the nucleosynthesis of heavy elements andto a rotating stellar collapse leading to a black hole that couldaccompany a supernova-like explosion, for the prediction of forthcomingobservational results.

Modern Meson Spectroscopy: the Fundamental Role of Unitarity
2022-05-31 15:00 - 18:00 | Online

Stars as Dark Matter cosmic laboratories: from the main-sequence to the horizontal branch
2022-05-31 15:30 - 17:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
Resumo A Matéria Escura (ME) é uma pedra angular do nosso entendimento do Universo. A validade do modelo ΛCDM implica que as galáxias estão rodeadas por um halo de matéria massiva e não bariónica, cujas interações continuam a eludir os nossos esforços experimentais. Caso estas partículas interajam com a matéria bariónica, elas vão acumular no interior das estrelas, onde subsequentes interacções com o plasma estelar poderão causar efeitos na estrutura e na evolução destas estrelas. O estudo destes efeitos é importante por duas razões: por um lado, pode contribuir para o nosso conhecimento acerca de física estelar; por outro, os efeitos podem ser testados contra observações de alta precisão com o objectivo de limitar as propriedades da ME. Nesta Tese estudamos a fenomenologia das interações de ME numa variedade de estrelas e assumindo o paradigma de partículas massivas com fracas interações (WIMP). Ao considerar diferentes tipos de estrelas podemos tirar partido dos diferentes processos físicos que as caracterizam para explorar novas formas de estudar ME usando observações astronómicas. Para completar esta tarefa criámos um módulo que permite modelar todos os processos relacionados com ME durante a evoluçao estelar. Este módulo funciona em conjunto com um código de evolução estelar open-source, e juntos formam um laboratório único onde podemos testar as hipóteses propostas nesta Tese. Usando estas ferramentas estudamos três cenários astrofísicos: o impacto do transporte de energia por ME assimétrica na estrutura e evolução de estrelas de baixa massa da sequência principal; os efeitos da produção de energia pela aniquilação de ME no centro de estrelas do ramo das gigantes vermelhas; e o impacto de interacções de ME na astrosismologia de estrelas do agrupamento vermelho. Ainda estudamos as incertezas presentes na modelação do espaço de fase do halo de ME e o seu impacto nos estudos referidos acima. No geral, obtivemos o resultado que enquanto que atuais limitações experimentais reduzem a capacidade dos métodos propostos nesta Tese de competirem com experiências concebidas para estudar a ME directamente, desenvolvimentos num futuro próximo desbloquearão o potencial único de estrelas como laboratórios de ME. Para finalizar, notamos ainda que a versatilidade das ferramentos numéricas desenvolvidas nesta Tese permite que o módulo possa ser melhorado e usado para estudar aplicações para além das estudadas nesta Tese.

High-precision measurement of the W boson mass with the CDF II detector
2022-06-01 11:00 - 13:00 | Online
Abstract:The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. The Higgs boson was the last missing component of the model. After the observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model. We measure the W boson mass using data corresponding to 8.8 inverse femtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 TeV center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. The measured value is in tension with the prediction of the model.

Black-Hole Neutron Star Simulations with BAM code
2022-06-02 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:With the first detections of black hole-neutron star (BHNS) mergers (GW200105 and GW200115) by the LIGO-Virgo-Kagra Collaboration a significant scientific breakthrough was achieved. The physical interpretation of pre-and postmerger signals requires careful cross-examination between observational and theoretical modelling results. In this talk, I will briefly introduce the BAM numerical relativity code and its capabilities in simulating compact object mergers. I will then present our work on simulating excision initial data (ID) of BHNS binary constructed using the publicly available LORENE ID solver and evolved using moving puncture gauge choices. Constrained solved and consistent ID are essential in accurately modeling compact object systems and a wider coverage of the parameter space is needed in exploring the dynamics of such systems. In this regard and with the availability of robust ID solvers like FUKA (public) and Elliptica (inhouse) we are able to explore a wider parameter space with accurate ID. Finally, I will report some improvements in the simulations using ID from these solvers.

Astrophysics in Cold Atoms: Photon Bubble Turbulence
2022-06-08 08:00 - 10:00 | Online
A pesquisa relatada neste manuscrito é dedicada ao estudo da dinâmica turbulenta que surge em átomos ultra-frios em condições de propagação incoerente de luz. Átomos frios são produzidos numa armadilha magneto-óptica iluminada por seis feixes de laser independentes. Para iluminação quase ressonante, os átomos interagem uns com os outros por processos frequentes de absorção e reemissão de fotões, que são espalhados várias vezes. À medida que o detuning dos lasers de arrefecimento e aprisionamento é aproximada da transição eletrônica, a propagação da luz torna-se aleatória, resultando num aprisionamento eficaz de radiação. Em tais condições, o fluido atômico é remexido por complexas dinâmicas espaço-temporais. A densidade atômica nos regimes estável e turbulento é examinada por meio duma técnica pumpprobe que desenvolvemos ad-hoc. O objetivo deste diagnóstico é superar as limitações devidas à integração da linha de visão que são comuns em métodos normais de espalhamento e absorção. Assim, somos capazes de visualizar diretamente a distribuição de densidade interna da nuvem atômica e caracterizar a sua estrutura espacial. Neste manuscrito descrevemos com precisão a configuração da diagnóstica e os princípios de funcionamento, e detalhamos os procedimentos experimentais e de análise que permitem investigar a estrutura local das flutuações da densidade atômica. As observações são então comparadas com as soluções analíticas para o modelo de turbulência de bolhas de fotões em átomos frios. Este modelo teórico é apoiado por simulações numéricas que permitem estender a sua validade para nuvens não homogêneas. Os resultados experimentais são consistentes com a descrição da turbulência impulsionada pela radiação difusiva e que se desenvolve no fundo do arrefecimento e aprisionamento dos lasers. A dinâmica turbulenta surge do crescimento e colapso contínuo das bolhas de fotões: a estrutura local de densidade média é caracterizada por um tamanho bem definido, exibindo assim, notavelmente, uma distribuição estatística não Kolmogorov. Esta tese contribui para fortalecer a analogia fluidodinâmica entre sistemas astrofísicos dominados por pressão de radiação e átomos ultrafrios produzidos em armadilhas magneto-ópticas. Essa semelhança pode ser útil para testar tanto as previsões de modelos complexos de plasma espacial quanto as técnicas sofisticadas aplicadas às medições de objetos espaciais.

Core-collapse and binary mergers in scalar-GaussBonnet gravity
2022-06-09 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In the present talk, we will discuss the dynamics of spontaneous scalarization of black holes and neutron stars in scalar-Gauss-Bonent gravity. We will focus on two particularly interesting nonlinear and highly dynamical scenarios for (de)scalarization - binary black hole merger and stellar core collapse. The gravitational wave signatures that are a smoking gun of the (de)scalarization will be discussed.

How to Talk to a Science Denier
2022-06-15 16:00 - 17:00 | Online, zoom
Title:How to Talk to a Science DenierAbstract:It's sometimes claimed that trying to convince a science denier with facts will only backfire. The latest research, however, shows that this is mistaken and that there ARE effective techniques that can be used to keep someone from becoming a science denier and even help them to overturn mistaken beliefs once they are formed. The secret lies in recognizing that even empirical beliefs may be held for reasons that have nothing to do with evidence, such as personal values, trust, ideology, and group identity. The best way to convince someone in this case is not to berate them, or clobber them with evidence, but engage in an examination of the cognitive and normative reasons why they reject factual evidence in the first place.Zoom Link:https://videoconf-colibri.zoom.us/j/82812777433?pwd=[REDACTED]

Family symmetries and Flavour
2022-06-15 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: I review the Flavour problem of the Standard Model and then discuss the most promising solution, family symmetries. I present how this type of symmetries can solve the flavour problem of the Standard Model and other extensions Beyond the Standard Model.

Synchronized bosonic hair: equilibrium solutions
2022-06-21 14:00 - 16:00 | Online
Resumo:Bosonic fields can spin down rotating black holes (BHs) via superradiance. If massive, they may remain trapped in the vicinity of a BH and endow it with hair co-rotating in synchrony with the event horizon. An illustrative example of this mechanism is the family of BHs with synchronized hair, that can co-exist with Kerr BHs and emerge dynamically from them at some scales. In this talk, I will first explore the features of BHs with vanishingly little (scalar and vector) hair, drawing their similarity to the atomic orbitals of the electron in a hydrogen atom. Then, I will discuss how hairy such BHs can become from the growth and saturation of superradiant instabilities. Finally, I will show how massless bosonic fields can also bind to BHs and form synchronized clouds.

Defect and strain profiles caused by ion implantation in GaN
2022-06-21 15:00 - 17:00 | Sala QA1.1 - Pavilhão de Química
ResumoO Nitreto de Gálio (GaN) é um semicondutor de hiato largo, com alta mobilidade eletrónica e alto campo de disrupção. Estas características permitem a operação em regimes de alta tensão, temperatura e frequência, tornando o GaN muito desejado na área da eletrónica de potência. A manipulação de algumas das suas características pode ser obtida através de implantação iónica. Apesar das suas vantagens, esta técnica implica a criação de defeitos e tensão no material, prejudicando o seu funcionamento e eficiência. Implantação iónica com európio (Eu) e silício (Si) foi feita em amostras de GaN, com o objetivo de estudar os efeitos da mesma. A evolução de danos e de tensão com a fluência foram estudados usando Retrodispersão de Rutherford em modo de Canalização, e Difração de Raios-X, respetivamente. Métodos analíticos e computacionais foram usados para extrair os perfis de defeitos e tensão com a profundidade. Medidas de stress in-situ foram feitas nas amostras implantadas com Si de modo a estudar a evolução do stress.Os perfis de defeitos obtidos são concordantes entre diferentes técnicas, e consistentes com os perfis de tensão, para ambas implantações. A evolução dos perfis com a fluência de implantação sugere transformações de defeitos, nomeadamente de defeitos pontuais para estruturas de defeitos mais complexas. Estes processos estão associados à relaxação do stress e da tensão, observados tanto nos perfis de tensão como nos resultados do stress. Modelos quantitativos e qualitativos para a evolução de danos e stress no material são propostos, com base nos resultados obtidos experimentalmente.

Multi-Higgs Doublet Models
2022-06-22 09:00 - 11:00 | Online
AbstractThis thesis is aimed at the study of softly-broken $A_4$ or $S_4$ 3 Higgs Doublet Models. Regarding these, two topics are discussed. In the first they are studied via the introduction of parameters that softly break the respective symmetries but preserve the directions of the vacuum expectation values of the triplet. Within this regime, we first conduct an analysis of the masses of physical states, highlighting common properties in the mass spectra of the extended scalar sector. Beyond this, we focus on the decay properties of these particles, with the goal of identifying dark matter candidates. We have identified a particular case where these candidates are accommodated without any further restrictions on the model.The second topic concerns an adaptation of a geometric method so that it suits softly-broken potentials. We discuss aspects to be taken into account so that our proposed method can be successful.This is then exemplified in an application to the softly-broken $S_4$ symmetric potential with general diagonal soft-breaking parameters. We conduct a complete determination of all the possible neutral minima the model can have in these circumstances, as well as necessary conditions for these minima to occur.

Wind has its satellite: aeolus
2022-06-22 16:00 - 17:00 | PA1, Pavilhão de Matemática
The colloquium will focus on the European Space Agency's aeolus satellite. It will more generally address satellite engineering. aeolus was placed into orbit by a Vega rocket on August 22, 2018, from Kourou in French Guiana. Its mission is to measure the speed of the winds all around the Earth and up to 30 kilometers in altitude. The mission is a world first, completed and a success. The data is great and is daily used for weather forecast. We will share a bit of the history, emotions and scientific and technical knowledge of aeolus. The basic principles of aeolus are simple and can be understood by everyone without any prior technical or scientific knowledge. The conference will cover the mission of aeolus, the orbit and its constraints, some technical elements of the construction of aeolus, the principles of measurement, the telescope, the laser, some of the major difficulties and how they were resolved. We will talk about terminator, cargo, soap bubbles, red lights, Lego, pressure cooker, black light, magnetic field detector possibly.

The conformal Killing spinor initial data equations
2022-06-23 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:We obtain necessary and sufficient conditions for an initial data set for the vacuum conformal Einstein field equations to give rise to a spacetime development in possession of a Killing spinor. The fact that the conformal Einstein field equations are used in our derivation allows for the possibility of the initial hypersurface intersecting non-trivially with (or even being a subset of) null infinity. For conciseness, these conditions are derived assuming that the initial hypersurface is spacelike. Hence, in particular, these conformal Killing spinor initial data equations encode necessary and sufficient conditions for the existence of a Killing spinor in the development of asymptotic initial data on spacelike components of null infinity.

Applications of the Wigner function to quantum problems involving angle variables
2022-06-28 14:00 - 16:00 | Sala P12, Piso 2, Pavilhão Matemática, Campus da Alameda
In this thesis the model of the Quantum Pendulum is studied in the Wigner function representation and in the Density Operator representation. Towards this end a completely solvable auxiliary model is introduced. Several families of solutions of the stationarity equations are found and compared. The advantage of using the Wigner function in the discovery of these solutions is made evident. A simpler approach to the derivation of the evolution equations is developed. Links with Mathieu functions and the Helmholtz equation of classical mathematical-physics are analized.

7ª MEFT Workshop
2022-06-29 09:00 - 14:00 | Anfiteatro Abreu Faro
Convidamos a comunidade do Instituto Superior Técnico a participar na 7ª Workshop dos alunos do mestrado de Engenharia Física Tecnológica. Neste encontro os alunos apresentam os projetos de investigação que vão fazer no âmbito Dissertação de Mestrado.O encontro vai decorrer na quarta-feira 29 Junho, das 9h00 às 13h00 no Anfiteatro Abreu Faro. O programa da workshop encontra-se neste link.Esta workshop é parte integrante da disciplina “Projeto Integrador de 2º Ciclo em Engenharia Física Tecnológica” do curso de mestrado de engenharia Física Tecnológica.A Comissão Organizadora: alunos da disciplina “Projeto Integrador de 2º Ciclo em Engenharia Física Tecnológica”

Coupling of multiple proton driven wakefield accelerator stages
2022-06-29 09:00 - 11:00 | Sala C10, Piso 1, Pavilhão Central, Campus da Alameda
AbstractThe AWAKE experiment aims to accelerate leptons to the TeV regime. It will accomplish its goal with a highly energetic proton beam as a wakefield driver. However, to increase the magnitude of the acceleration gradients produced by the driver, one must extend its propagation distance. Prolonging the current stage would be experimentally challenging due to the self-consistent evolution of the ionisation front used during this stage.We propose adding a pre-formed plasma stage, to the existing stage, where the half-modulated beam (result of the first stage) can propagate. This work aims to study how the wake of the unmodulated part interacts with the modulated part of the beam during the second stage. We first analysed the impact of various wakefield parameters on the structure of the modulated beam, and concluded that the wake's phase is the most relevant parameter for the conservation of the beam. Next, we analysed in detail the propagation of a partially modulated beam. The results showed that seeding the modulation of the unmodulated part is the best approach to guarantee higher acceleration gradients during the second stage.Lastly, we demonstrated that we can adjust the length of the simultaneously accelerating and focusing region of a wakefield produced by two sources, by controlling their width, and the spacing between them. This is an important result that allows us to increase the accelerator's efficiency, by increasing the number of efficiently accelerated particles.

Shadow of a Black Hole in Loop Quantum Gravity and its super-radiance property
2022-06-30 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:We will discuss the shadow calculation of the loop quantum gravity motivated regular black hole recently proposed by Ashtekar, Olmedo and Singh (AOS black hole hereafter). In the process, we also construct the rotating loop quantum gravity inspired solution of the originally proposed static spherically symmetric AOS black hole by applying the modified Newman-Janis algorithm. We study the quantum effects on the shadows of both the non-rotating and rotating loop quantum black hole solutions. It is observed that the general shape of the shadow for nonrotating AOS black hole is circular in shape as is expected for its classical counterpart too, but the presence of loop quantum gravity inspired modification contracts the shadow radius and the effect reduces with the increase in the mass of the black hole. On a similar note, in the rotating situation, we find contraction in shadow radius due to quantum effects and the tapered nature of the shadow as expected from the classical Kerr case. However, instead of the symmetrical contraction, like non-rotating one, we found more contraction on one side relative to the other when we compare our result with the shadow of the Kerr black hole. We finally studied super-radiance in rotating AOS background and observed that the super-radiance condition for massless scalar field is identical to that of the Kerr case with the rotation of the BH being more compared to Kerr in the low mass regime. With an increase in mass of the rotating AOS black hole, the difference from Kerr starts to become insignificant. We also perform the calculation of the super-radiance amplification factor using Teukolsky formalism in the AOS background and present a comparative study of the amplification factors of the AOS and Kerr black holes with respect to changing mass and spin of the holes.

11º Encontro "LEFT | A desafiar os limites em ciência e tecnologia"
2022-07-01 09:00 - 18:00 | VA3 (Pavilhão de Engª Civil)
É um encontro destinado aos alunos do ensino secundário (e a vocês), para falarmos de uma forma descontraída e informal sobre a "Licenciatura em Engenharia Física e Tecnológica" no IST, e faz 10 anos que arrancámos com estes encontros com futuros candidatos à LEFT/MEFT.As manhãs são dedicadas a [muitas] micropalestras (máximo de 10 minutos cada), sobre [super]temas da atualidade em física, aplicações, percursos, etc...A tarde de 6ªFeira (15h00–18h00) será dedicada às visitas aos laboratórios.1 de julho, 6ªFeira, 9h00–18h00,2 de julho, sábado, 9h30–13h00.Os alunos e professores podem inscrever-se diretamente na página do encontro.Mais informações na página do evento.

Neutrino masses and the origin of matter through leptogenesis
2022-07-04 15:00 - 17:00 | Sala QA1.2, 1, Torre Sul, Campus da Alameda
AbstractThe properties of particles and antiparticles are firmly established in collider physics. They appear to be on the same footing in the Standard Model, which naturally poses the question of why the observed Universe is composed nearly exclusively of matter, in contrast to little or no primordial antimatter.Despite its remarkable success in describing many of the inner workings of Nature at its most fundamental level, the Standard Model struggles to explain the existence of a biased Universe. A compelling possibility is that the baryon asymmetry of the Universe is generated dynamically, a scenario that is known as baryogenesis, which implies the non-conservation of the baryon number B. In the past thirty to forty years, several mechanisms for baryogenesis have been put forth: grand unified theory baryogenesis, electroweak baryogenesis, Affleck-Dine mechanism, spontaneous baryogenesis.Nonetheless, the most compelling one is the mechanism of baryogenesis via leptogenesis, first proposed by Fukugita and Yanagida, whose simplest and theoretically best motivated realization is within the seesaw mechanism of neutrino masses.In this thesis, we discuss the mathematical implementation of leptogenesis in the context of type-I seesaw mechanism. Additionally, we consider the evolution of the baryonic asymmetry during the course of different temperature regimes, discriminating between the unflavoured and flavoured treatment of leptogenesis. Lastly, we take into consideration the importance of decoherence effects in transition regimes, which leads us to opt for an alternative description under the formalism of density matrix equations.

Flight data analysis of the BERM radiation monitor aboard the BepiColombo mission to Mercury
2022-07-05 08:30 - 10:30 | Online
AbstractBepiColombo is the first European mission to the Hermean system. It was launched in 2018 and is predicted to enter Mercury’s orbit in late 2025. It is composed of two spacecraft, ESA's Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (nicknamed Mio).Among the instrument suit of the MPO is the BepiColombo Radiation Monitor (BERM), that can detect high energy protons (~1 to 200 MeV), electrons (~1 to 10 MeV) and heavy ions. BERM is part of the spacecraft housekeeping, with the objective of monitoring radiation hazards to prevent possible damage on the spacecraft and instruments. Despite not being part of the scientific payload, its capability of measuring such high energies and its operational state during all phases of the mission makes it an asset for scientific objectives as well. BERM consists of a single stack with 11 Silicon detectors interleaved by aluminum and tantalum absorbers. BERM identifies particles type and energies through the signals resultant from its interaction with the stack, assigning each particle to one of 18 channels: five dedicated to electrons, eight to protons, and five to heavy ions. The monitor provides daily files with the number of registered counts in each channel integrated over 30 seconds sampling intervals. Obtaining particle fluxes from the BERM channel counts is not straightforward. In this work, the bow-tie method, introduced by Van Allen in 1979, was applied to convert flight count rates to proton and electron fluxes. The results were used to analyze solar events detected by BERM.(Contactar Ana Bela Cardoso para password) ana.bela.cardoso@tecnico.ulisboa.pt

Mini magnetospheres in the laboratory
2022-07-07 14:00 - 16:00 | Online
AbstractThe interaction between plasmas and magnetic obstacles often occur in astrophysical and space environments such as in ion-scale “mini magnetospheres”. Such systems display a wide range of physical mechanisms and provide a unique environment for studying kinetic-scale plasma physics. In this work, we present collisionless particle-in-cell (PIC) simulations of ion-scale magnetospheres that reproduce recent laboratory experiments performed on the Large Plasma Device (LAPD) at UCLA. In our PIC simulations, a driver plasma flows against a dipolar magnetic field that is embedded in a uniform magnetized background plasma. The simulations replicate the main magnetospheric structures observed in the experiments, namely the magnetopause and the plasma current distributions. We show the formation of a magnetic cavity and a magnetic compression and two main current structures in the dayside region. From multiple parameter scans, we show a reflection of the magnetic compression, bounded by the length of the driver plasma, and a higher separation of the main current structures for lower dipolar magnetic moments. Additionally, we develop a analytical model that characterize the coupling between the driver and the magnetized background plasmas. The model is compared with the simulations, showing good agreement.(Contactar Ana Bela Cardoso para password) ana.bela.cardoso@tecnico.ulisboa.pt

A tale of old super metal-rich stars
2022-07-07 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:During this presentation, I will describe the work I developed during the past ~1.5 yr in the scope of the Gaia-ESO survey, which has recently been made completely public (Randich et al. 2022 A&A accepted; Gilmore et al. 2022 A&A submitted). I will focus this presentation on a sample of old super metal-rich stars currently inhabiting the Solar vicinity analysed in Dantas et al. (2022a, A&A in review). Several chemo-dynamic parameters (along with their ages and super-metallicity) indicate that they have migrated from the inner regions of the Milky Way, including orbits of low eccentricity (e≲0.2), maximum height from the Galactic plane between ~0.5-1.5 kpc, and lack of radial metallicity gradient. These results are in accordance with several other works in the literature (e.g. Kordopatis et al. 2015) and predictions from simulations (e.g. Khorpeskov et al. 2020). I will end my presentation by showing an additional analysis of the effects of radial migration on lithium abundances of these stars which will be submitted in the shape of a letter (Dantas et al. 2022b, A&A letters - to be submitted).

Higgs-Dilaton inflation in Einstein-Cartan gravity
2022-07-14 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Gravity can appear in different incarnations, from the commonly used metric formulation to the Palatini, teleparallel and Einstein-Cartan ones. Despite the difference in the choice of the fundamental degrees of freedom, all these formulations are equivalent in pure gravity scenarios, leading to the same equations of motion, therefore being devoid of any observational consequence. However, this equivalence is broken in the presence of a non-minimal coupling to matter, such as the Standard Model Higgs.Such coupling opens the possibility for the Higgs field to be responsible for the inflationary phase in the early universe. In this talk, I will discuss the phenomenology of Higgs-Inflation in the context of Einstein-Cartan gravity, together with its scale-invariant version, the so-called Higgs-Dilaton model. In particular, I will show how the Einstein-Cartan formulation can endow a rich phenomenology, due to the unavoidable presence of extra gravitational operators, and interactions with fermionic matter. In a second part, I will discuss how this scenario can accommodate the formation of scalar compact objects in the early universe and the possible emission of gravitational waves.

Dynamics LFS and HFS density profiles at ASDEX Upgrade - Effect of magnetic configuration and divertor conditions
2022-07-18 14:00 - 16:00 | Online
Abstract:Future fusion devices, including ITER, will need to operate with a detached divertor regime. Divertor detachment is often linked to the formation of a high-density front on the high-field side (HFS) that significantly influences the profiles at the inboard midplane. HFS profiles are also remarkably sensitive to the magnetic configuration and, in particular, to the connection between the LFS and the HFS. The physics behind these observations is not yet fully understood as experimental data from the HFS is often scarce. The O-mode reflectometer at ASDEX Upgrade is a valuable tool as it allows measuring the density profiles both on the LFS and HFS. In this work, we investigate the influence of ballooning transport and the high-density front in establishing HFS density profiles using as main experimental tolls scans in the magnetic configuration and in the divertor conditions. Our observations have shown that the high-density region is limited to the flux surface containing the secondary X-point and leads to inverted density gradients very close to the inner separatrix.

Atribuição de grau Emeritus
2022-07-19 16:00 - 18:00 | Centro de Congressos IST
É com enorme prazer que convidamos toda a comunidade para a cerimónia de atribuição do título de Professor Emérito aos Professores Gustavo Castelo-Branco e Jorge Romão e do título de Investigador Emérito ao Dr. Emílio Ribeiro.O título de Investigador e Professor Emérito é conferido pela Universidade de Lisboa aos Investigadores e Professores já aposentados, reformados ou jubilados, que atingiram alto grau de projecção no exercício da sua atividade académica, que se destacaram na sua área de especialidade, pela relevância e/ou magnitude da sua produção e atividade científicas, desfrutando de grande reconhecimento pela comunidade académica.O Departamento de Física está a organizar uma Cerimónia de atribuição de Grau, a acontecer no dia 19/07 pelas 16h00, no Centro de Congressos do IST, a qual contará com a presença do Sr. Reitor da Universidade de Lisboa, do Presidente do IST e do Presidente do DF, anfitrião da cerimónia.Esperamos ver-vos a todos nesta cerimónia de homenagem a colegas que contribuiram para tornar o DF uma referência internacional.

Exotic Higgs bosons at the LHC
2022-07-20 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Any additional SM-like neutral Higgs boson is expected to be heavy as it would incur extremely tight constraints from electroweak precision tests as well as from its non-observation at the LHC. A class of flavor models exists which predicts exotic neutral Higgses which, unlike the SM Higgs boson, do not have couplings to VV pair (V = W,Z), and their Yukawa couplings are purely flavor off-diagonal (tc, tu, bs, bd, ... type, without having any uu, tt, bb, ... type diagonal couplings). By virtue of these two properties they can bypass the stringent constraints mentioned above, provided the off-diagonal Yukawa couplings are not too large to attract some other constraints. Such exotic states can be light. The sizes of those flavor off-diagonal Yukawas are generally fixed by the requirement of correct reproduction of the quark masses and mixing in specific flavor models. But in this talk I shall take a model independent approach -- simply assume the presence of one such scalar and a pseudo-scalar - both light - having off-diagonal Yukawa couplings whose sizes are restricted by flavor observables, and focus on how to dig out those states from the LHC data.

Structured laser--plasma interactions at ultra-high intensities
2022-07-20 15:00 - 17:00 | Online
Abstract Light can carry and transfer a well-defined orbital angular momentum (OAM) [1] along the propagation axis and is often called twisted light. This quality opens new research in highly non-linear (I 1022 W/cm2) laser-plasma interactions, including magnetic field generation [2], electron/positron acceleration in laser-plasma accelerators [3], high orbital angular momentum harmonic generation [4], and direct laser acceleration of ions [5]. However, the full potential of twisted light interacting with plasma is yet unexplored. We studied three novel scenarios analytically and through three-dimensional particle-in-cell simulations using OSIRIS [6]; enhanced proton acceleration, the light properties in the cutoff region of plasma, and wakefield acceleration through light with self-torque. The main project focused on proton acceleration. By exploiting the benefits of a high-intensity twisted light pulse impinging a double-layer target, we could reduce the accelerated proton bunch divergence by almost an order of magnitude while maintaining its energy compared to the conventional Gaussian method [7]. Here, we identified that relativistic self-focusing in the near-critical plasma layer of the target and the light's OAM contents play a crucial role in improved proton acceleration. We also explored light springs and light with self-torque by combining twisted light modes. First, a study of the properties of a light spring in the cutoff region of plasma has shown a similar characteristic behavior as a compressed mechanical spring [8]. Second, we identified that a wakefield configuration with self-torque in the non-linear regime leads to azimuthal forces and the formation of quasi-helical electron beams [9]. Twisted light is still an open field in laser-plasma research and has the potential to lead to new regimes of particle acceleration, radiation processes, and eventually laser fusion research.

The impact of dark matter on compact stars and their merger dynamics
2022-07-21 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Compact stars due to their enormous gravitational field can accumulate a sizable amount of dark matter in their interior. Depending on its nature, an accumulated dark matter may affect the properties of neutron stars in quite different ways. I will give an overview of the impact of dark matter on various observable properties of neutron stars, i.e. the mass-radius relation, tidal deformability, surface temperature, merger dynamics and gravitational wave waveform, etc. For two scenarios, asymmetric fermionic and bosonic dark matter, the conditions at which dark matter particles tend to condensate in the core of the star or create an extended halo will be presented. I will show how dark matter condensed in a core tends to decrease the total gravitational mass and tidal deformability compared to a pure baryonic star, which appears as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo has an opposite effect, causing an increase of those observable quantities. Thus, observational data on compact stars could be affected by an accumulated dark matter and, consequently, constraints we put on the strongly interacting matter at high densities. I will discuss how the ongoing and future X-ray, radio and gravitational wave observations could shed light on dark matter admixed compact stars and put multi-messenger constraints on thecorresponding effect.

The Ionising Radiation Environment in the Solar System
2022-07-21 16:00 - 18:00 | Online

Quantum Algorithms for Experimental High-Energy Physics Data Processing
2022-07-26 14:00 - 16:00 | Online
Abstract:Quantum computers can solve various problems more efficiently than classical computers. While there are still no large-scale quantum computers, one can study the complexity of quantum algorithms and understand which ones have a theoretical advantage over their classical counterparts. In this presentation, I propose new quantum algorithms for the object reconstruction problems of tracking and clustering, which occur frequently in the context of particle physics data analysis. The goal of these problems is to group the data points according to some specified geometrical rule. Using amplitude amplification routines, I show that a polynomial quantum speedup is reachable assuming coherent access to the classical input data. I will finish the presentation by mentioning undergoing work on other object reconstruction problems, both in fault-tolerant and restricted-depth settings.

The Future Circular Collider: Recent development in physics and detector studies
2022-09-06 14:30 - 16:30 | Online
Abstract:Along the path defined by The European Strategy for Particle Physics, a financial and technical feasibility study of the FCC colliders and their infrastructure has been carried out for the next upgrade of the strategy around 2025/6. The FCC program combines in the same 100km infrastructure a high luminosity Higgs and Electroweak factory e+e- collider, FCC-ee, followed by a 100 TeV hadron collider. The main challenges of the current effort are both about physics potential and performance studies and for detector design to fully exploit its potential, while being technically feasible and affordable on the project time scale (start of operations around 2040). The most striking detector challenges will be highlighted, then focusing on the IDEA experiment proposed for the FCC-ee by the INFN Italian community. While providing a global view of the IDEA subdetectors and the new technologies used , more details will be given about the project of an ultra-low mass Drift Chamber as the central tracking system of IDEA.

Qualification and Diagnostics development for the European Shock-Tube for High-Enthalpy Research
2022-09-08 14:00 - 16:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract:The ESTHER shock tube is a new state-of-the-art facility at Instituto Superior Técnico to support future ESA planetary exploration missions. The facility recreates the re-entry plasma conditions sustained by a hypersonic velocity atmospheric entry. These shock wave velocities are in the range of 4 to 14 km/s range. A high-pressure combustion chamber using a mixture of He:H2:O2 ignited by a high-power Nd:YAG laser acts as the driver. A qualification campaign was carried out with 100 shots and evaluating the effects of air:fuel ratio, filling pressure, inert gas dilution and ignition mode. These parameters directly affect the produced shockwave velocity and should be effectively controlled.Alongside the driver qualification the development of different diagnostics is presented, namely the VUV spectroscopy system and a compact reflectometer/interferometer for space applications. Technical requirements and architecture of a reflectometry/interferometry equipment tailored for both ground-test facilities (shock-tubes and plasma wind-tunnels) and flight experiments are proposed.A simulation of electromagnetic environment for the RAM-C flight experiment, obtained using a CFD code coupled to an electromagnetic propagation code is presented, outlining the adequacy of such a diagnostic for improving verification and validation for high-speed entry plasma flows.

Searching the Invisible Universe through the stars and beyond
2022-09-08 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: In this talk I review some bounds on light dark matter, derived from astrophysical observables. I focus on axion and axion-like particles, as well as on dark photons. I present constraints on these particles from MS stars, Globular Clusters and compact objects, and some recent results about dark photons obtained by my collaborators and me. In addition, I discuss a future work on the Lyman-alpha forest, in order to elucidatethe role of axions as dark matter candidates.

The Interstellar Medium of the Most Luminous Galaxies, Near and Far
2022-09-15 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Most galaxies in the universe spend their lives inhabiting what is called the main-sequence (MS) of star-formation, a peaceful and gentle state in which galaxies form stars and feed their central massive black holes (BHs) in a steady manner.However, simulations and observations suggest that, at least once in their life-times, galaxies undergo a merger event during which their star formation efficiencies and BH accretion rates drastically increase over a short period of time.This phase in galaxy evolution occurs behind a thick blanket of dust and gas that obscures the central, very luminous power source(s). The study of this incredibly luminous galaxy population is therefore fundamental to our understanding of the main physical processes that drive the evolution of galaxies over cosmic time.In this talk I will present results obtained from infrared observations of nearby and high-redshift luminous infrared galaxies, for which in-depth studies of their interstellar medium have been only recently made possible by the advent of state-of-the-art telescope facilities such as Herschel, ALMA, and now JWST.

Solar neutrinos: Shining light on neutrino properties
2022-09-21 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:In this talk, I will review the contribution of solar neutrinos to our currently well-established three-neutrino oscillation picture and the prospects for the study of neutrino properties beyond masses and mixing. Firstly, I will discuss how next-generation experiments JUNO and Hyper-Kamiokande will provide strong constraints on non-standard interactions while determining the oscillation parameters with unprecedented precision. Then, I will also show how, in the case of Majorana neutrinos, the non-observation of a solar antineutrino flux can set limits on neutrino magnetic moments. Finally, I will briefly review other constraints on neutrino properties from solar neutrinos.

Unconventional ways to measure the Hubble constant with lensed and non-lensed supernovae
2022-09-22 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The precise determination of the Hubble constant has gained enormous attention after a discrepancy between local and early-universe measurements has become evident with the release of the first data from the Planck satellite almost 10 years ago. Since then, this discrepancy, known as the "Hubble tension", has grown to more than 5 sigma, and may hint at new physics beyond the LambdaCDM standard model of cosmology. I will present two projects that aim to use supernovae to measure the Hubble constant in the local universe. Both methods provide stand-alone one-step measurements that are completely independent of the distance ladder. In the first approach, the "adH0cc" collaboration augments the classical expanding-photosphere method with tailored spectral modelling to determine distances of Type II supernovae. The method is applied to spectral time series of supernovae in the Hubble flow obtained through a dedicated ESO Large Programme. In the second approach, the "HOLISMOKES" team aims to use supernovae that are strongly lensed and multiply imaged by a massive foreground galaxy. By measuring the temporal delays between their multiple images, the so-called time-delay distance and hence the Hubble constant can be inferred. From both programmes we expect measurements with 5% precision within the next years.

The study of the impact of angular momentum transport in low mass red giant stars using asteroseismology
2022-09-22 16:00 - 18:00 | Sala C10, Piso 1, Pavilhão Central, Campus da Alameda
Computational and analytical models predict several mechanisms of transport of angular momentum (AM) and of mixing of chemical elements capable of describing some of the physical phenomena in star’s interiors through their evolution. Nonetheless, recent measurements of core rotation rates of red giants enabled by the Kepler mission, indicating a possible missing AM transfer mechanism in the current theory of stellar interiors.In the first part of this work, we use the Modules for Experiments in Stellar Astrophysics (MESA) stellarevolution code to compute models of low mass rotating stars from the zero-age main sequence (ZAMS) to the red giant branch (RGB) calibrating them to a specific Kepler asteroseismic target, KIC8579095.We include transport of AM and rotation-induced chemical mixing due to magnetic fields in radiative zones, using the Tayler-Spruit dynamo formalism and the recent revision by Fuller et al. (2019) (named Fuller-formalism), which has showed very promising results for red giant models. We also make use of the adiabatic pulsation code, GYRE, to further study this mechanisms using asteroseismic observables. We find that only the models including the Fuller prescription for AM transport were able to predict the observed core rotation rates on the RGB. The efficiency of transport of AM increases with inclusion of mixing, predicting lower rotation rates in the RGB, despite the mixing induced by the Fuller-formalism being extremely small as expected.In the second part, we tested the efficiency of AM transport of Fuller-formalism models with different input physics: stellar mass, metallicity, convective overshooting and the free parameter of this theory. We found models particularly sensible to variations in initial mass, but less to metallicity and overshooting. Lastly, using a sample of 1093 stars with masses in the 1-2 solar mass range that include all the stellar evolution phases from main-sequence (MS) up to the red clump (RC), we study the transfer of AM through these phases. To that end, we modeled a typical star with a mass of 1.5 M and compared the results obtained with asteroseismic observations for this group of stars. We found that a wider range for the α parameter [0.5;5] in the Fuller-formalism is needed to reproduce the particular measurements of RGB and RC stars.

Characteristic formulations of general relativity and applications
2022-09-26 16:00 - 18:00 | Online
Abstract:General relativity can describe various gravitational systems of astrophysical relevance, like black holes and neutron stars, or even strongly coupled systems through the holographic duality. In addition, more formal aspects of the theory like the stability of spacetimes and the formation of singularities are still topics of active research. In several cases, solutions in closed analytic form are not known, and perturbative methods are inadequate, leading to the employment of numerical techniques. The characteristic initial (boundary) value problem has numerous applications in general relativity involving numerical studies and is often formulated using Bondi-like coordinates. Well-posedness of the resulting systems of partial differential equations, however, remains an open question. The answer to this question affects the accuracy, and potentially the reliability of conclusions drawn from numerical studies based on such formulations. A numerical approximation can converge to the continuum limit only for well-posed systems. The notion of well-posedness is tightly related to that of hyperbolicity and includes the specification of a norm. In the first part of this thesis, we expand our understanding of the hyperbolicity and well-posedness of Bondi-like free evolution systems. We show that several prototype Bondi-like formulations are only weakly hyperbolic and examine the root cause of this result. In a linear analysis we identify the gauge, constraint and physical blocks in the principal part of the Einstein field equations in such a gauge, and we show that the subsystem related to the gauge variables is only weakly hyperbolic. Weak hyperbolicity of the full system follows as a consequence in many cases. We demonstrate this explicitly in specific examples, and thus argue that Bondi-like gauges result in weakly hyperbolic free evolution systems under quite general conditions. Consequently, the characteristic initial (boundary) value problem of general relativity in these gauges is rendered ill-posed in the simplest norms one would like to employ. We discuss the implications of this result in accurate gravitational waveform modeling methods and work towards the construction of alternative norms that might be more appropriate. We also present numerical tests that demonstrate weak hyperbolicity in practice and highlight important features to perform them effectively. In the second part, we turn our attention to applications of these formulations to strongly coupled systems via holography. We expect these studies to shed more light on the qualitative behavior of strongly coupled plasmas, but due to weak hyperbolicity, we cannot perform rigorous error estimates to our satisfaction. We present Jecco, a newly developed characteristic code that allows us to simulate the dynamics of strongly coupled plasmas. Representative examples of the simulations that can be achieved with this code are provided, namely the out-of-equilibrium dynamics of said plasmas that undergo phase transitions. This is a putative scenario of the early universe and such simulations might provide insights into questions of fundamental nature.

Open Questions in S3-Symmetric Three-Higgs-Doublet Models
2022-09-29 11:00 - 13:00 | Sala de Seminários do DF, 2º Piso do Pavilhão de Física
Abstract: The main focus of the research is to check for possible Higgs-like dark matter candidates within three-Higgs-doublet models with an underlying S3 symmetry. In our framework the stability of the dark matter sector results from a Z2 symmetry which survives the breaking of S3. We catalogue all possible dark matter models within this framework. Furthermore, two models (with and without CP violation in the Higgs potential) are explored based on theoretical and experimental constraints. After applying a number of successive checks over the parameter space we found different viable dark matter mass regions within the range of [6, 90] GeV depending on the model. Further work is under way along these lines.

Robinson–Trautman solutions in (2+1) dimensions
2022-09-29 14:30 - 16:30 | Sala de Reuniões e Seminários do DF (2-8.3) (2nd Floor of Physics Building)
Abstract:The Robinson-Trautman (RT) spacetime is the simplest solution of General Relativity (GR) describing a compact source surrounded by gravitational waves. As an initial value problem, the RT spacetime evolution is a well-posed mathematical problem. The pertinent dynamical equations are equivalent to the so-called Calabi flow, and regular initial data evolve smoothly towards a final state corresponding to a remnant Schwarzschild black hole. Extensions of RT spacetimes for higher dimensions (D > 4) were recently proposed, and the essence of the RT evolution is unchanged: regular initial data evolve towards a final higher-dimensional Schwarzschild black hole. The situation for D=3 is quite different due to some peculiarities of low-dimensional GR. We will present a D=3 RT flow mimicking the essential properties of the Calabi flow. In particular, regular initial data evolve towards a final remnant BTZ black hole, and any possible asymmetry in the initial data is expelled as a radiation fluid.

Black holes and hot shells in the Euclidean path integral approach to quantum gravity
2022-10-06 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Microscopic gravitational systems involving black holes and matter present quantum and thermodynamic properties that are worth of study.Due to the breaking of the vacuum from a strong gravitational field near the event horizon of a black hole, particles, such as gravitons or other matter fields, are emitted to infinity with a definite temperature, the Hawking temperature. Left by itself, a black hole loses mass in this emission process until it eventually disappears.To understand more deeply the connection and conversion between black holes and hot matter fields, one has thus to enclose the black hole and the hot matter inside a heat reservoir which is maintained at constant temperature and constant radius, and which in turn characterizes the canonical ensemble of statistical mechanics. A thermodynamic treatment for the system black hole plus hot matter is then possible. We model the hot matter fields by a hot thin shell that surrounds a black hole and is inside the heat reservoir.To work out the quantum partition function, from which the thermodynamics of the system emerges, we use the Euclidean path integral approach to quantum gravity that identifies the path integral of the gravitational system with the partition function itself. In a zeroth order, semiclassical, evaluation of the path integral, one computes the Euclidean classical action of the system which, at this order, is equal to the system's thermodynamic free energy divided by the temperature. Several important consequences related to the energy, the temperature stratification, the entropy, and the thermodynamic stability of the system unfold in a natural way.A most significant result is the finding of the various possible thermodynamic phases of the ensemble, specifically, pure black hole spaces, pure hot shell spaces, hot shell with a black hole spaces, and hot flat spaces, and the establishing of the possible phase transitions between them through the identification of the ground state phase of the ensemble once a temperature equation of state for the matter in the hot shell is given. Yet another result connected with the conversion of pure black holes into curved spaces with hot matter in the form of hot thin shells and vice versa, is that the systems in some instances perform as black hole thermodynamic mimickers and in another instance act as authentic dynamic and geometric mimickers. The precise setting and all these results will be explained in some detail along the seminar.

Quantum correlations: from quantum mechanical foundations to applications
2022-10-12 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:In this talk, I will introduce quantum correlations, one of the key aspects of quantum information theory, starting with the seminal example of Bell nonlocality. I will review Bell’s theorem, which shows how quantum mechanics cannot be simulated classically.Generalizations of Bell nonlocality and other types of quantum correlations will be outlined. Experimental research and applications of quantum correlations will be briefly discussed, with a focus on quantum communication using quantum optics and light-matter interaction.

On well-posedness of relativistic theories for viscous fluids
2022-10-13 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Much effort has been invested during the last decades with the aim to develop a theory for dissipative fluids in the context of General Relativity. One of the difficulties that appear to that end is the parabolic nature of heat propagation, which seems to go against the causality principle imposed by Einstein's theory. This problem makes the issue of modelling relativistic viscous fluids a highly non-trivial task.In this talk we shall review previous and current attempts at dissipative fluid theories. After recalling the necessary conditions for a general hydrodynamic theory to be well-posed, stable and causal, we shall point out some issues that appear when studying the corresponding initial-value formulation and finally comment on future challenges and open problems, both from the analytic and numerical perspectives.

Recepção aos novos alunos
2022-10-14 15:00 - 16:00 | Centro de Congressos do Técnico, Pavilhão de Civil
O DF vai dar as boas vindas aos novos alunos do LEFT e MEFT, dia 14 de Outubro. A recepção vai incluir uma descrição do departamento e dos eventos mais extraordinários dos últimos anos. Durante este evento, vamos ouvir ex-alunos do DF, incluindo Frederico Fiúza (actualmente Group Leader no SLAC, Stanford), e alunos actuais como o Rafael Almeida. Vamos convidar o NFIST a mostrar-se e as novas caras do DF a apresentarem-se. E temos uma surpresa para todos.

Primordial Black Holes as laboratories for Physics beyond the standard scenarios
2022-10-18 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:We use the evaporation of primordial black holes (PBHs), of mass between 10^8 -10^12 kg, as a laboratory to investigate Physics beyond the Standard Model of particles and to probe the structure of black holes.We show that PBHs develop non-negligible spins through Hawking's emission of a large number of axion-like particles generically present in string theory compactifications. This is because scalars can be emitted in the monopole mode (l = 0), where no angular momentum is removed from the BH, so a sufficiently large number of scalars can compensate for the spin-down produced by fermion, gauge boson, and graviton emission. This yields a unique probe of the total number of light scalars in the fundamental theory, independent of how weakly they interact with known matter.We propose a method to determine the mass and spin of PBHs based on measuring the energy of specific features in the photon Hawking emission spectrum, including both primary and secondary components. Since the proposed method relies on the energy of the photons emitted by a given PBH, rather than on the associated flux, it is independent of the PBH-Earth distance and, as a byproduct, can also be used to infer the latter.We study a regular rotating black hole, described by the Kerr-black-bounce metric, evaporating under the Hawking emission of a single scalar field. We compare the results with a Kerr black hole evaporating under the same conditions. The Gray-body factors, the asymptotic final spin, the surface gravity, and as a consequence temperature, primary emissivity, and lifetime, are affected by the regularizing parameter. We briefly comment on the possibility of investigating the beyond-the-horizon structure of a black hole exploiting its Hawking emission.

Conformal model for gravitational waves and dark matter. A status update
2022-10-19 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: We present an updated analysis of the first-order phase transition associated with symmetry breaking in the early Universe in a classically scale-invariant model extended with a new SU(2) gauge group. Including recent developments in understanding supercooled phase transitions, we compute all of its characteristics and significantly constrain the parameter space. We then predict gravitational-wave spectra generated during this phase transition and by computing the signal-to-noise ratio we conclude that this model is well testable (and falsifiable) with LISA. We also provide predictions for the relic dark matter abundance. It is consistent with observations in a rather narrow part of the parameter space, as we exclude the so-called supercool dark matter scenario based on an improved description of percolation and reheating after the phase transition as well as inclusion of the running of couplings. Finally, we pay special attention to renormalisation-scale dependence of the results and even though our main results are obtained with the use of renormalisation-group improved effective potential, we also present the outcome of a fixed-scale analysis. It proves that the dependence on the scale is not only qualitative but also quantitative.

The subtle importance of collective motions on isotropic Magnetic and non-magnetic ionic liquid systems
2022-10-19 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:In recently published works aiming to study the paramagnetic properties of magnetic ionic liquids using 1H NMR relaxometry and diffusometry, X-ray diffractometry revealed, for some of the studied systems, a well-defined local structure motivated by the segregation of the polar and non-polar domains [1]. Although these compounds did not present the same degree of order as a liquid crystal, it was only possible to consistently combine the data from all experimental techniques considering order parameter fluctuations as a possible relaxation pathway.The present work combines 1H NMR relaxometry and diffusometry with X-ray scattering experiments in the study of the molecular dynamics of magnetic and non-magnetic ionic liquids based on the [P6,6,6,14]+ and [C8mim]+ cations. The data from all experimental techniques corroborated the need to consider either order parameter fluctuations or layer undulations in the model fitting analysis of these ionic systems, despite their apparent isotropic nature.

Gravitational waves – from theory to detection to astrophysics
2022-10-20 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Gravitational waves bring us rich insights into the astrophysics of black holes and neutron stars. Detecting and interpreting these signals has been the culmination of decades of work on precision interferometry, mathematical general relativity, numerical relativity, signal modelling, and data processing. I will focus on numerical relativity and waveform modelling, with a summary of the field’s history, the most recent advances, and how and what they have taught us about the universe – and what is still to come. Finally, I will discuss one of the latest results, the first measurement of strong-field general-relativistic precession.

Study of the Spin/CP properties of the Higgs coupling to W-bosons with ATLAS at the LHC
2022-10-26 09:30 - 11:30 | Online (Meeting ID: 657 2811 7852 Passcode: [REDACTED]
Abstract:Sources of CP violation beyond the Standard Model (SM) are necessary to account for the observed matter-antimatter asymmetry in the Universe. Despite the significant progress in the experimental exploration of the Higgs sector in the last ten years and the overall agreement of the current results with the expectations of the SM, the experimental precision is not yet sufficient to constrain anomalous Higgs boson interactions. The work presented here focuses on the search for CP violation in the HWW interaction vertex in events where a Higgs boson is produced in association with a W boson, when the Higgs decays to a pair of b-quark jets and the W boson to a charged lepton and a neutrino. Several groups have proposed different observables to search for anomalous couplings in the HWW vertex. In order to optimise the experimental sensitivity to such couplings, the most promising angular observables proposed in the literature were compared to novel machine-learning inference methods that allow building (statistically) optimal observables without approximating the detector response. The results show that a combination of energy-related and angular observables is competitive with the current version of the tested machine-learning inference techniques.All these methods require the best possible experimental resolution in the measurement of the final state particles. The identification of b-jets, as well as the measurement of their energy and momentum, is very challenging experimentally and requires dedicated calibration samples, as well as analysis techniques. Collecting large, unbiased samples of jets for calibration requires an efficient and optimised jet trigger system. The ATLAS jet trigger was upgraded for Run 3, introducing full-event scan tracking and calorimeter+track jet reconstruction. This presentation will also cover several studies done to study and optimise the jet's trigger efficiency and CPU costs.

Quantum algorithms for jet clustering
2022-10-26 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Experimental High-Energy Physics, especially the Large Hadron Collider programme at CERN, is one of the most computationally intensive activities in the world. This demand is set to increase significantly with the upcoming High-Luminosity LHC, and even more in future machines, such as the Future Circular Collider. As a consequence, event reconstruction, and in particular jet clustering, is bound to become an even more daunting problem, thus potentially challenging present day computing resources. In this talk, I present the two quantum algorithms to tackle this problems and, in particular, the first digital quantum algorithm to for jet clustering, opening the way for digital quantum processors to address this challenging problem. Furthermore, we show that, at present and future collider energies, our algorithms have at least comparable complexity relative to the classical state-of-the-art $k_t$ clustering algorithm

Nuclear technology and engineering studies on reflectometry systems for ITER and DEMO
2022-10-27 09:00 - 11:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
Resumo A fusão nuclear controlada é umas das soluções mais promissoras para o aumento da procura por formas mais sustentáveis de produção de energia eléctrica à escala global. No caminho a percorrer até à comercialização de energia eléctrica produzida através da fusão, o reactor DEMO, desenvolvido pelo consórcio EUROFusion, é um passo intermédio entre o ITER (em construção) e os reactores comerciais do futuro. Tokamaks de grandes dimensões como o ITER e o DEMO requerem redes complexas de sistemas de diagnóstico, que permitam controlar o plasma de forma fiável por longos períodos de operação. Entre estes, a reflectrometria de microondas já demonstrou ser uma forma alternativa de controlo, capaz de monitorizar a densidade, a posição e a forma do plasma com elevada resolução espacial e temporal. Esta tese apresenta estudos de design e engenharia para dois sistemas de diagnóstico desenvolvidos pelo IPFN/IST: o sistema de reflectometria de posição de plasma (PPR) do ITER e um sistema com múltiplos reflectómetros proposto para o DEMO. Devido à natureza das medições, alguns dos componentes destes sistemas estarão expostos directamente ao plasma, sujeitos a elevados fluxos de neutrões de alta energia (14 MeV) que contribuirão para as cargas térmicas nos componentes e poderão ter como efeito alterar as propriedades dos materiais, pondo em risco a sua integridade mecânica durante os períodos de funcionamento dos reactores. Por esta razão, estudos complexos de design (envolvendo neutrónica, análises termo-mecânicas e simulações electromagnéticas) são cruciais para garantir que os diagnósticos sobrevivem aos ambientes de radiação do ITER e do DEMO sem comprometer o seu desempenho. Para o sistema PPR do ITER, o software ANSYS Mechanical foi usado para estimar as temperaturas de operação dos componentes mais expostos, em duas posições distintas, conhecidas como gaps 4 e 6. Nas configurações estudadas, os resultados mostram que as antenas do sistema PPR estariam sujeitas a temperaturas superiores ao limite estabelecido pelo ITER para o aço inoxidável sob 1 irradiação, mesmo após várias tentativas de optimização. Tendo em conta estes resultados, diferentes materiais foram propostos para as antenas. Apesar de a Organização ITER ter descontinuado o desenvolvimento do sistema PPR, o conhecimento adquirido durante os estudos de integração e desenvolvimento continua a ser válido para o desenho do sistema de reflectometria proposto para o DEMO. Para este sistema, um conceito de integração proposto previamente – Diagnostics Slim Cassette (DSC) – foi desenhado e avaliado. Os códigos CATIA V5, MCNP e ANSYS foram usados para desenhar o sistema e estimar fluxos de neutrões e radiação gama, cargas térmicas e temperaturas de operação, assim como o impacto que essas condições de operação terão nas medições de reflectometria. As análises nucleares e termo-mecânicas apresentadas neste trabalho demonstram a viabilidade do conceito e a capacidade do sistema para operar no ambiente de radiação do reactor DEMO, de acordo com os padrões estabelecidos pelo código RCC-MR. Este resultado é obrido com uma configuração simplificada do sistema de arrefecimento, possível de fabricar com técnicas convencionais. Os resultados e as metodologias implementadas nesta tese podem servir como directizes para outros sistemas de diagnostico, nomeadamente aqueles em que a DSC possa servir como possível solução de integração.

Optimization and Evaluation of Solar Powered Electric Rickshaw
2022-10-27 09:00 - 11:00 | Anfiteatro QA1.3, Piso 1, Torre Sul, Campus da Alameda, IST
Os veículos elétricos são considerados uma opção mais viável no combate da emissão dos gases de efeito de estufa no sector de transporte. No entanto, um dos problemas que impedem a adoção global dos veículos elétricos é a autonomia limitada, o que leva ao fenómeno de “ansiedade de alcance”. A produção fotovoltaica integrada em veículos elétricos é uma possível alternativa para este problema. Ao incorporar a tecnologia fotovoltaica no teto do veículo, o sistema de baterias do mesmo pode ser carregado durante a condução ou mesmo quando o veículo está em estacionamento. Por outro lado, o emprego desta tecnologia permite subdimensionar as baterias, originando uma poupança directa no investimento capital do veículo e nos custos de operação.O foco principal desta tese é, pois, otimizar a gestão de energia das baterias dum Riquexó elétrico com base num histórico diário de percursos, quantificando a viabilidade tecno-económica quanto à existência de mercado para estes veículos. Com o sistema proposto, implementado e estudado nesta tese foi possível observar, num dia típico ensolarado em meia estação, um aporte em média dum suplemento de 35% da energia elétrica consumida pelo veículo. A análise económica do sistema proposto previu um Retorno de Investimento (ROI) de 185% ao longo da vida útil do veículo de 6 anos.Note-se que, devido ao cariz sazonal do veículo em que é esperado um maior consumo em dias de sol devido às suas características turísticas, estas poupanças podem ser levadas praticamente ao limite duma redução similar à capacidade energética das baterias.

Data acquisition system for the magnetics diagnostics in COMPASS-U
2022-10-27 11:30 - 13:30 | Online
COMPASS-U will be a new magnetic fusion experiment, designed to support the operation of ITER and to serve as a stepping stone on the road to DEMO, addressing key challenges in its construction and design. As such it will be a high magnetic field device (5T), supporting high densities and power fluxes relevant to ITER and DEMO. As with any magnetic fusion device magnetic diagnostics are fundamental for both plasma control and scientific studies. The requirements placed on the acquisition system for these diagnostics are not readily found in the market and a custom design has the potential to fulfil them at a lower cost. The design of a data acquisition system satisfying the requirements of the magnetic diagnostics in COMPASS-U is presented. The carrier board under design is based on a FPGA SoM and is compatible with existing isolated 2MSPS ADC modules. This module confers flexibility to the design and allows the functionality of the board to be extended to suit other data acquisition applications requiring a high number of channels and a high volume of data at a low cost per channel.(Password: [REDACTED] Meeting ID: 932 4201 1237)

The Weiss variation in gravitation theory
2022-10-27 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The Weiss variation formalism in mechanics and classical field theory concerns action variations that include explicit endpoint/boundary displacements. The Weiss variation is useful in field theory because it can be used to obtain expressions for the conjugate momenta and Hamiltonian without performing an explicit 3+1 decomposition beforehand. In this talk, I review the Weiss variation in mechanics, classical field theory, and in gravitation. In general relativity, one can recover (by way of an auxiliary connection formalism) a tensorial generalization of the Einstein canonical energy-momentum pseudotensor, as well as a reference-dependent Hamiltonian. In addition to discussing the Weiss variation in general relativity, I comment on some applications of the Weiss variation formalism for modified gravity theories.

Exotic tetraquarks with heavy quarks in lattice QCD
2022-11-02 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
We review all the different direct and indirect approaches that lattice QCD has beenemploying to study multiquarks, focusing in the tetraquarks with heavy quarks. Wealso briefly review the experimental progress in observing tetraquarks, and the mostrepresentative models of tetraquarks, comparing them with the results of lattice QCD.Since the discovery of quarks and the development of the QCD theory, there has beena large interest in exotic hadrons, initiated by the tetraquark models developed byJaffe in 1974. In the new millennium, this interest exploded with several experimentaldiscoveries of tetraquark resonances with heavy quarks, starting with the $Z_c$ and$Z_b$. Moreover there is a second class of tetraquarks such as the $T_{bb}$,boundstates in the sense of having no strong decays. Very recently, the narrow$T_{cc}$ tetraquark first predicted with quark models in 1982 Richard et al, wasobserved experimentally. Lattice QCD, being a first principle approach to solve nonperturbative QCD, has been crucial not only to compute precise results, but also tomotivate and inspire research in hadronic physics, with particular interest in exotichadrons. So far, lattice QCD has not yet been able to comprehend the $Z$ class oftetraquarks, while it predicted the $T$ class of tetraquarks. New methods are beingdeveloped to determine the masses, decay widths and decay processes of tetraquarks.

Gravitational waves from phase transitions with holography
2022-11-03 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT:With the advent of Gravitational Wave (GW) astronomy a new door into learning about properties of matter has been opened. In particular, gravitational waves coming from a first order phase transitions are expected to be detectable by next generation experiments. These are assumed to proceed via the nucleation, expansion and collision of bubbles. An accurate prediction of the spectrum implies computing out-of-equilibrium properties of quantum field theories, which are challenging even at weak coupling. This offers a golden opportunity for holography to make an impact on astrophysics and cosmology. In this talk I will review recent progress in the context of cosmological phase transitions, including a possible alternative mechanism of GW emission, and neutron star mergers.

Twisting quantum matter beyond the graphene paradigm
2022-11-08 16:00 - 17:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The ability to control and manipulate the strength of correlations inquantum matter is one of the central questions in condensed matterphysics today. While pressure, chemical doping, or magnetic field haveserved as conventional tuning knobs for a wide class of correlatedsystems, the ability to twist van der Waals materials has recentlyemerged as a novel scheme to engineer strong correlations and tuneelectronic properties. For example, when two sheets of graphene aretwisted to a "magic angle," the kinetic energy of the electronic degreesof freedom vanishes and, as a result, interaction effects dominate. Thishas now been demonstrated experimentally following the discovery ofsuperconductivity in close proximity to correlated insulating phases inmagic-angle graphene.In this talk, I will first discuss our theory that describes themagic-angle phenomena as a universal property of Dirac points in anincommensurate potential. This allows us to generalize the magic-angleeffect to a wide class of models and distinct physical settings, such asultra-cold atomic gases, trapped ions, and metamaterials. This generalperspective will then be used to demonstrate how unconventionalsuperconductors can be manipulated via a twist. These results will thenbe applied to describe recent experiments on twisted slabs of thehigh-temperature superconductor

Quantum matter outside equilibrium- an update
2022-11-09 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
In the first part of this talk, I will describe what has kept me and my collaborators busyover the past year. My goal here is to keep you - the local community - up to date onwhat we have been doing and foster discussions and collaborations. In the secondpart of the talk, I will focus on one of the ongoing scientific projects that is part ofMiguel Oliveira’s Ph.D. thesis. In this work, we ask what is the fate of a Mott insulatorwhen a bias voltage, \delta\mu, is applied across the system. Our goal is to understandwhat kinds of non-equilibrium phases are realized as the voltage increases and what isthe nature of the non-equilibrium quantum phase transitions between them. Weconsider a model system consisting of a half-filled t-V chain coupled to leads, thatfeatures spineless fermions with nearest neighbor interactions and where both theequilibrium (\delta\mu=0) and the Markovian (\delta\mu\to\infty) limits are known. Iwill describe our progress and the challenges we have been facing.

Building consistent Multi Higgs Models
2022-11-10 08:00 - 10:00 | Online
Nesta tese consideramos uma das mais simples extensões do setor escalar do Modelo Standard: Modelos de N dubletos de Higgs (NHDM). Primeiro estudamos o potencial escalar mais geral com uma simetria exata. Provamos que tal modelo exibirá um limite de desacoplamento se e só se o vácuo também satisfizer a mesma simetria. Esta propriedade geral também é mostrada independente e explicitamente para modelos com três dubletos de Higgs, considerando em detalhe todos os modelos com uma simetria e os seus possíveis vácuos. Depois, estudamos dois 2HDM invariantes sob as simetrias Z2xPi2 e U(1)xPi2. Para o primeiro, provamos que não é possível estender a simetria para os fermiões de forma compatível com as observações experimentais (massas de quarks, ângulos de mistura, e Jcp não nulos), enquanto que para o segundo mostramos que é possível, existindo apenas uma extensão. Seguidamente, consideramos um 3HDM com uma simetria A4 exata. Fornecemos as condições analíticas completas, necessárias e suficientes para um ponto ser mínimo global nas direções neutras, discutindo também algumas subtilezas subjacentes que salientamos através de exemplos numéricos. Após isto, estudamos as direções que quebram a carga elétrica e apresentamos condições analíticas suficientes que garantem Boundedness from below (BFB). Para estas direções, baseados num conjunto extenso de simulações numéricas, discutimos também uma conjetura sobre BFB. Finalmente, consideramos a adição de termos, ao potencial escalar, que quebram suavemente a simetria A4 num modelo com três dubletos. Nesse, estudamos numericamente as extensões de A4 ao setor fermiónico, concluindo acerca da sua compatibilidade com as observações experimentais.

B Physics Anomalies from Dark Matter
2022-11-10 09:00 - 11:00 | Online
Resumo:Neste trabalho estudamos uma extensão do Modelo Padrão ao comparar dois modelos que explicam a origem de indícios de violação de universalidade de sabor dos leptões para o decaimento b sl+l-, o momento anómalo do muão e o problema da matéria escura (ME). O decaimento do quark e a anomalía do muão são explicados através de diagramas com loops onde participam os candidatos a ME. Para além dos campos do Modelo Padrão, os modelos têm um campo fermiónico sem cor, um campo escalar sem cor e um com cor. Num dos modelos, o fermião é um dubleto de e os escalares são singletos de enquanto no outro modelo o fermião é um singleto de e os escalares são dubletos de . Após estudarmos a fenomenologia de sabor e matéria escura dos modelos, fizemos um scan de forma a encontrar o espaço de parâmetros dos modelos que explica os três fenómenos de nova física simultaneamente. Concluímos que ambos os modelos conseguem explicar não só todos os problemas mencionados anteriormente mas também outros problemas de sabor e ME. Contudo, existem diferenças cruciais na forma como as restrições na ME afetam os dois modelos, resultando numa diferença considerável nos valores permitidos para a massa de ME.

Jet substructure tools to identify hadronization timescales
2022-11-16 11:00 - 13:00 | Pavilhão de Civil, Anfiteatro VA1
Quantificar as escalas da transição entre os regimes perturbativo (pQCD) e não-perturbativo (npQCD) da Cromodinâmica Quântica é um problema de raiz da Física de Partículas. Enquanto que pQCD aplica-se aos partões (quarks e gluões), partículas finais (detetáveis) enquadram-se no regime npQCD. Estas designam-se por hadrões, partículas compostas produzidas via hadronização. Para adquirir conhecimento relativo ao processo de hadronização, esta tese propõe o uso de jets como ferramenta de análise, que são estruturas de partículas finais às quais sequências de clusterings são atribuídas como proxies da história evolutiva das partículas. Usando jets de diferentes regiões cinemáticas e colisões de diferentes energias de centro de massa como instrumentos de seleção da espécie partónica predominante na iniciação dos jets, são realizados estudos de subestrutura que revelam que gluões produzidos em colisões energéticas tendem a iniciar jets mais largos, simétricos e céleres que os quarks. Este documento contém estudos adicionais focados na fração de momento groomed, que mede a simetria de uma emissão em termos de momento transversal, e no tempo de formação, um proxy para as escalas temporais das emissões. Estes mostram que a seleção de jets baseada em tempos de formação permite a identificação da etapa de declustering na qual as duas partículas carregas mais energéticas se desacoplam. Também revelam que este processo marca claramente na sequência de clusterings a transição de propriedades típicas de pQCD para propriedades atípicas deste regime.

Logic: A Guided Tour
2022-11-16 14:30 - 15:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Consequence system. Consequence system induced by a calculus and by asemantics. Soundness and completeness. Classical and intuitionistic logics.Metatheorems.

Continuous Measurements in Quantum Transport Setups
2022-11-17 10:00 - 12:00 | Online
Password Acesso Zoom: 464728Estudamos sistemas dissipativos Markovianos descritos por Liouvilianos fermiónicos e quadráticos. Apresentamos um novo esquema de vetorização que nos permite obter os resultados principais presentes em [1] para o espectro e estado estacionário de um Liouviliano quadrático. Inicialmente consideramos o caso de Liouvilianos genéricos construídos a partir de um Hamiltoniano quadrático aleatório e canais de dissipação lineares e também aleatórios. Variando a intensidade da dissipação e o número destes canais por fermião, m=M/(2NF), encontramos duas fases distintas onde o suporte do espectro single-body tem uma ou duas regiões conexas. No regime fortemente dissipativo, esta transição ocorre a m=1/2 e é concomitante com uma mudança qualitativa tanto no estado estacionário como no hiato espectral.Além disso, estudamos sistemas de transporte, descritos por Liouvilianos quadráticos, sob medições contínuas ou ruído. Primeiro, foi estudado uma cadeia acoplada a reservatórios Markovianos com dephasing induzido por ruído estocástico ou medições contínuas locais. Foi fornecida uma abordagem alternativa aos resultados obtidos em [2]. Para uma análise mais profunda foi estudado o formalismo Large Deviations e desenvolveu-se um método capaz de eliminar instabilidades numéricas na implementação de evoluções de matrizes densidade geradas por superoperadores gerais, quadráticos e que não conservam o traço. Este método é outro resultado original desta tese e acaba por ter aplicações consideravelmente mais amplas, pois determina como proceder de forma geral para obter a evolução temporal de qualquer sistema quadrático, aberto ou fechado sob ruído ou medições. Por fim, aplicamos este método a uma cadeia fermiónica com medições continuas.

Sun-like stars with Earth-like and Mercury-like planets
2022-11-17 14:30 - 16:30 | Sala de Reuniões e Seminários - 2-8.3
Abstract:Because of their common origin, it is expected (or assumed) that the composition of planet building blocks should (to a first order) correlate with stellar atmospheric composition, especially for refractory elements. In fact, information on the relative abundance of refractory and major rock-forming elements such as Fe, Mg, Si are commonly used to improve interior estimates for terrestrial planets and has even been used to estimate planet composition in different galactic populations. However, there is no direct observational evidence for the aforementioned expectation/assumption and was even recently questioned. In this talk I'll present our latest results where showed that the composition of the planet building blocks indeed correlates with the properties of the rocky planets.

Optimisation studies for the pion-induced Drell-Yan measurement at the AMBER experiment
2022-11-23 09:00 - 11:00 | Online
Resumo:AMBER é uma experiência futura de alvo fixo no CERN. Foi aprovada recentemente e um dos objetivos de física da primeira fase é o estudo do processo Drell-Yan induzido por um pião.Drell-Yan consiste na aniquilação de um quark e um antiquark originando um fotão virtual que decai no estado final para um par de muões com cargas opostas. Este processo garante um acesso privilegiado à estrutura do pião. Desta forma, a contribuição da valência, do mar e dos gluões no pião serão caracterizadas com precisão sem precedente. AMBER usará feixes de piões de alta intensidade e energia, de ambas as cargas, a interagir com diferentes alvos nucleares.A configuração experimental de AMBER é baseada na da experiência COMPASS, introduzindo upgrades significativos ao espectrómetro já existente. Assim, a otimização da região do alvo de AMBER para as medidas de Drell-Yan está a ser estudada e é o objetivo deste trabalho.Neste trabalho, introduzimos uma cadeia de simulação de Monte Carlo que permite a simulação do processo físico e do espectrómetro, a resposta dos detetores e a reconstrução dos dados obtidos. Assim, vamos estudar o impacto da introdução de detetores de vértice e como diferentes posições, geometrias e segmentações afetam os resultados.Neste estudo, o detector de microstrips de silício FVTX parece a opção mais sólida para o detetor de vértice. A escolha baseia-se nos valores obtidos para a resolução em massa e na posição Z do vértice, assim como na aceitância global de dimuões.

Assembly and characterization of the magneto-optical Kerr effect magnetometer
2022-11-23 10:30 - 12:30 | Online
(Contactar Ana Bela Cardoso para password) ana.bela.cardoso@tecnico.ulisboa.ptResumoUm dos passos mais importantes na indústria de dispositivos magnetoresistivos é a caracterização do comportamento magnético de multi-camadas de filmes através de curvas de histerese. É necessário quantificar várias propriedades magnéticas para a fabricação bem controlada de novas aplicações, como anisotropia magnética, acoplamento de troca, etc, que são críticos para a operação de dispositivos. Estas são determinadas por técnicas sensíveis de magnetometria, uma das quais sendo o efeito magneto-óptico de Kerr que faz uso de luz polarizada. Tal montagem possui a vantagem, por exemplo, de ser capaz de realizar medidas locais com boa resolução espacial, em contraste com o magnetómetro de amostra vibrante ou o dispositivo de interferência quântica supercondutora, com tempos de aquisição rápidos e requerendo nada mais que uma montagem simples de bancada. Desta forma, este é o magnetómetro ideal para complementar as capacidades e objetivos de investigação do INESC MN.De modo a conceber a montagem, uma análise teórica juntamente com simulações numéricas foram realizadas para provar que a medida de uma curva de histerese era possível e como esta se relacionava com a intensidade do sinal, a rotação de Kerr e a elipticidade de Kerr. Para além disso, estas também cobriram os requisitos necessários à montagem em termos de ruído, estrutura de amostras e eletroíman. Concluiu-se que a medida ideal deverá ser realizada através de uma medida diferencial com amplificador lock-in, usando usando uma camada até 30 nm no topo da hetero-estrutura. Para além disso, verificou-se que, por forma a obter campos magnéticos fortes, da mesma ordem que os campos de inversão em junções de efeito de túnel, a solução de eletroíman a implementar deverá incluir um núcleo ferromagnético.Depois, o magnetómetro foi construído nas geometrias transversal e longitudinal de acordo com a análise anterior. A presença de obstáculos relacionados com o ruído nos circuitos de aquisição DC e AC propostos, levaram uma vez mais à aplicação de um amplificador lock-in na montagem.Para validar as montagens construídas, amostras de NiFe foram depositadas e medidas nas mesmas, demonstrando a sua sensibilidade a variações da magnetização das amostras. No entanto, a rotação de Kerr não foi possível medir na geometria longitudinal, muito provavelmente devido a ruído proveniente do divisor de feixe polarizado. Adicionalmente, observou-se que a deposição de CoFe/Ta e CoFe/Ru para espessura variável da camada de topo e a sua subsequente medida na montagem longitudinal, coincidiam muito bem com os resultados das simulações.Apesar de ainda apresentar espaço para melhorias, a montagem tem vindo a mostrar continuamente a sua precisão e utilidade na caracterização de estruturas magnéticas. Ademais, tem o potencial para a implementação de mais funções como o acréscimo de uma nova geometria, a inclusão de um ambiente controlado ou a observação de domínios magnéticos através de um dispositivo de carga acoplada.

Building up DNA (and other molecules), bit by bit
2022-11-23 15:30 - 17:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The properties of large aggregates of particles, be they colloidal clusters ormacromolecules, often depend crucially on the precise arrangement of their buildingblocks. Examples are the nature of the de-mixing in reacting polymer blends; theability of some elastomers to exhibit strain-induced periodic textures; or the selfhealing nature of some copolymers over a narrow range of compositions. However, theactual sequence of building blocks is not usually experimentally accessible: knowing itwould allow, e.g., the reverse engineering of structures with desirable behaviours. Wedevelop a simple theory that treats self-assembly as reversible chemical reactions. Wethen apply this to the assembly of DNA copolymers from two types of duplexes, asdescribed by the oxDNA model. We find that the theory reproduces well the statisticsof chain lengths from simulations. Our results suggest that theories incorporating verylimited molecular detail may be useful for predicting the broad equilibrium features,and even some kinetic aspects, of copolymerisation.

Linearized General Relativity on Hyperboloidal Slices
2022-11-23 16:00 - 18:00 | Anfiteatro EA3, Pavilhão de Torre de Electricidade
O tratamento do infinito nulo futuro na Relatividade Numérica é ainda um problema em aberto. A sua relevância deve-se ao facto de ser o único “local” no espaço-tempo onde a radiação gravitacional pode ser medida de forma inequívoca, e de corresponder também à idealização adequada de observadores de eventos astrofísicos. A precisão das formas de onda extraídas das simulações numéricas é crucial para estimar a correta propriedades das fontes de radiação gravitacional observadas pelos interferómetros. Atualmente, essas formas de onda são calculadas por extrapolação ou por extração/evolução Cauchy-característica. No entanto, esses métodos são insatisfatórios do ponto de vista de primeiros princípios. Neste trabalho, adotamos uma abordagem alternativa – o método hiperboloidal –, em que o espaço-tempo é foliado em hipersuperfícies espaciais que se estendem até ao infinito nulo futuro. Para isso, introduzimos novas coordenadas que compactificam o espaço-tempo. Nestas coordenadas, as equações de onda têm termos formalmente singulares, o que podemos superar considerando a taxa de decaimento dos campos e redimensionando-os tal que as equações se tornem regulares no infinito nulo futuro. Para entender melhor a taxa de decaimento dos campos, apresentamos o modelo good-ugly e mostramos que reproduz o comportamento das equações linearizadas de Einstein. Implementamos a abordagem hiperboloidal para as equações do modelo e mostramos que elas são regulares no infinito nulo futuro. Para a implementação numérica, usamos o código NRPy+, e resolvemos as equações em primeira ordem no tempo e no espaço com dados iniciais axialmente simétricos numa grelha que não inclui os extremos. Verifica-se convergência, indicando um resultado bem-sucedido. Uma abordagem semelhante pode ser feita para a Relatividade Geral completa, embora com complicações adicionais.

Sensitivity of jet sub-structure observables to jet quenching in collisions of light nuclei
2022-11-23 17:00 - 19:00 | Online
Através das colisões de iões pesados, tal como PbPb, é possível produzir o plasma de Quarks e Gluões (QGP) em aceleradores de partículas, como é o caso do Large Hadron Colider (LHC). A partir do fenómeno de jet quenching, em que partões muito energéticos formados em simultâneo com o plasma interagem com este, dando origem a jets de hadrões que são modificados relativamente às colisões em que tal meio não é criado (i.e colisões pp), é possível estudar as propriedades do QGP. Como tal, é crucial a existência de simuladores de Monte Carlo, como o JEWEL, que permitam explorar a fenomenologia de jet quenching. Contudo, o JEWEL não está idealizado para lidar com colisões não centrais e/ou entre núcleos mais leves. Estas últimas, embora estejam associadas com a produção de menos QGP, abrem portas para o estudo de processos mais raros e permitem mais precisão na medição de certos observáveis de jets. Inclusivamente, colisões OO vão ser realizadas no LHC durante a run 3.Este trabalho tentou otimizar o funcionamento do JEWEL para o limite da colisão de núcleos leves e/ou periféricas, substituindo o modelo de inicialização do meio, baseado na aproximação ótica, por um mais realista e adequado a este limite, baseado no modelo de Glauber Monte Carlo. Posteriormente, foi realizado um estudo intensivo de comparação entre estes dois modelos, onde se pode concluir que o tratamento mais realista conduz a diferenças substanciais no evento médio e nos valores obtidos para observáveis. Finalmente, utilizou-se o modelo construído para estudar variáveis de sub-estrutura de jets, em colisões de núcleos leves.

Geometrical aspects of jet quenching in small systems
2022-11-23 18:00 - 20:00 | Online
ResumoO início da nova fase de operação do LHC (Run 3), e consequente anúncio da futura realização das primeiras colisões de núcleos leves, marca o princípio de uma nova era na história da Física de Partículas, a qual exige aprofundar os estudos sobre colisões de sistemas pequenos. Contudo, esta tarefa não é fácil, pois atualmente os geradores de eventos Monte Carlo usados para explorar a fenomenologia do jet quenching falham no tratamento dos aspetos geométricos de jet quenching em sistemas pequenos. Daqui surge o primeiro objetivo desta tese: modificar o código do gerador de eventos Monte Carlo, JEWEL, de forma a melhorar a sua performance no tratamento de sistemas pequenos. Tal foi conseguido, essencialmente, através da alteração do modelo implementado em JEWEL para descrever a geometria da colisão inicial, o modelo Ótico de Glauber (MOG), substituindo-o pelo modelo Monte Carlo de Glauber (MMCG). Verificou-se que as principais diferenças entre os dois códigos ocorrem em colisões de núcleos leves e/ou em colisões periféricas, dado que o MOG, para além de não ser válido para núcleos leves, ignora a existência de flutuações na geometria da colisão inicial.Por fim, usando este novo gerador de eventos, realizou-se uma análise comparativa do jet quenching em sistemas de geometria diferente, mas tamanho igual, concluindo-se que, no que diz respeito à perda de energia por jet quenching, o Fator de Modificação Nuclear, , é sensível à geometria do meio.

Towards low noise, biaxial magnetic field imaging of electrical currents with magnetic tunnel junctions
2022-11-24 10:30 - 12:30 | Online
ResumoNesta dissertação, Junções de Efeito de Túnel (JETs) são exploradas no contexto de aplicações de Análise Não-Destrutiva por meio de inspeção do campo magnético produzidos por correntes eléctricas em dispositivos microeletrónicos. Um novo protótipo de sensores JET é proposto e testado, combinando deteção biaxial a baixo ruído do campo magnético. Um solução que combine deteção simultânea de duas componentes a baixo ruído do campo magnético é favorecida em detrimento da melhoria da resolução espacial, o que é sustentado pelos padrões de integração microelectrónica de estado-da-arte e por simulações das assinaturas magnéticas produzidas por configurações de correntes elétricas simples encontradas no contexto de falhas em microelectrónica. Os sensores baseados em JETs incorporam barreiras cristalinas de MgO, tendo sido depositados por pulverização catódica em magnetrão, ao que se seguiu a sua padronização em pilares com diferentes fatores de forma de modo a linearizar a sua resposta magnética. Estes pilares foram dispostos em série, em diferentes geometrias. Seguiu-se um único passo de recozimento na presença de um campo magnético aplicado a 45º, de forma a definir uma direção de referência comum entre os sensores. Simetria nas propriedades de magnetotransporte entre sensores de eixos diferentes, assim como robustez contra campos cruzados e sensitividades na zona linear oscilando entre 10-20 % / mT foram obtidos após fabricação. Um elevado acoplamento foi medido ao longo das direções sensíveis, para o qual diversas hipóteses de origem são avançadas e confrontadas com um modelo de Stoner-Wohlfahrt para o sistema em questão. Finalmente, medições de ruído foram efetuadas na ausência de campo, a partir das quais os parâmetros de qualidade foram calculados, tendo sido inferiores aos necessários na gama de aplicações a médio e longo alcance. Um reduzido produto resistência-área e anisotropia uniaxial induzida na camada livre das JETs são elencados como parâmetros fulcrais para uma abordagem bem sucedida ao complexo desafio de deteção biaxial a baixo ruído do campo magnético com JETs, cujo recozimento é feito num só passo, de modo a definir as duas direções sensíveis ortogonais.

Relativistic Dynamical System and Gravitational Waves
2022-11-24 14:30 - 16:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:After the discovery of the gravitational waves, gravitational wave physics and astronomy have provided us new information about strong gravitational phenomena and new physics. For example, speed of gravitational waves, equation of state at very high dense regions, constraint on gravitational theories, and so on.In order to observe gravitational waves, we have used the templates of emitted gravitational waves from a binary system. However, we may have a more complicated relativistic dynamical system in nature, which may not be integrable. We may expect chaotic behavior in such a system, for which it is very difficult to make appropriate templates.In this talk, we study chaos in a relativistic dynamical system of compact objects and the gravitational waves emitted from such a system. We then look for some characteristic features of the gravitational waves, which could be used in gravitational wave observation.We also discuss a hierarchical triple system with the Kozai-Lidov mechanism, which shows the oscillation between the eccentricity of inner binary and relative inclination. The evolution curve of the cumulative perihelion shift, which is indirect evidence of gravitational wave emission, will be bent since the gravitational waves are emitted strongly when the eccentricity becomes large. We then show the observability of gravitational waves from such a triple system. We also consider relativistic effects such as Lense-Thirring precession.

Dashboard Development for a Solar Electric Auto Rickshaw
2022-11-25 09:00 - 11:00 | Online
RESUMOO trabalho desenvolvido nesta tese baseia-se no desenvolvimento de um sistema de infoentretenimento a implementar num veículo solar eléctrico e capaz de fornecer informação acerca de detalhes gerais da viagem e uma estimativa do seu impacto ambiental.Para isso, o primeiro passo consistiu em instalar um sistema de paineis solares no veículo eléctrico para aumentar a autonomia do veículo e reduzir a sua dependência da rede elétrica. Com isto, a melhoria da vertente ambiental associada à utilização do veículo é incentivada.De seguida, um sistema de aquisição de dados foi configurado para transmitir dados adquiridos pelos sensores e relativos aos fenómenos mecânicos e elétricos relevantes. O Raspberry Pi foi então configurado para processar e armanezar os dados que sustentam o sistema de infoentretenimento e são analisados para extração de informação.Por fim, os sensores e a data adquirida foram utilizados para desenvolver o sistema de infoentretenimento. Para obter uma escolha mais ponderada de métricas a exibir no sistema de infoentretenimento, realizou-se um estudo de mercado. Com isso, o sistema de infoentretenimento foi desenvolvido e adaptado às necessidades e expetativas dos clientes e da empresa, transmitindo informação acerca dos detalhes gerais da viagem, a localização do veículo e o impacto da utilização do mesmo em termos ambientais e económicos.Com base nos dados recolhidos durante várias viagens, a simulação do sistema de infoentretenimento foi desenvolvida com sucesso. Recriando o funcionamento dos sensores, a plataforma é capaz de processar os dados e produzir as métricas para exibir no sistema de infoentretenimento.

Time-resolved studies of Warm Dense Titanium: A Bayesian search of coupling parameters
2022-11-28 14:00 - 16:00 | Sala P3, Piso 1- Pavilhão de Matemática
Plasmas densos e fortemente acoplados são difíceis de modelar graças à dificuldade de tratar as interações quânticas entre muitos corpos a temperaturas elevadas. As colisões electrão-electrão (e-e) e eletrão-ião (e-i) que determinam as propriedades básicas do plasma são difíceis de calcular. Além disso, isolar e medir as diferentes taxas de espalhamento em equilíbrio térmico é impossível. Aqui descrevemos uma experiência de "pump-probe" de femtossegundos em que se transforma uma amostra sólida num plasma para medir os acoplamentos e-e e e-i.Uma configuração experimental, que consiste num impulso de laser infravermelho ultracurto (〖10〗^14 W/〖cm〗^2, 50 fs, 800 nm), foi usada para criar plasmas de densidade sólida, com dezenas de eV de temperatura, na profundidade de penetração do Titânio. A estrutura eletrónica da amostra aquecida foi sondada com um impulso XUV de energia próxima da borda de absorção M_2,3. O perfil espacial dos impulsos XUV transmitidos foi gravado numa única medição com uma resolução de 10 μm, e foi resolvido espacialmente em intervalos de 50 fs, para um total de dezenas de picossegundos. Um mapa da transmissão XUV para fluências variáveis do laser foi então registado em cada aquisição. Os resultados mostram uma primeira excitação eletrónica do laser que dá lugar (no regime dos picossegundos) ao processo de equilibração e-i, com arrefecimento dos eletrões e recuperação da transmissão.Para interpretar os dados experimentais referentes ao primeiro picossegundo, um modelo foi construído usando teoria cinética de quântica. Assumiu-se um potencial de Coulomb blindado, aquecimento uniforme durante a profundidade de penetração, e um gás de eletrões quase livre a interagir com centros fixos de colisão e outras partículas de gás. Para a resposta temporal mais longa foi utilizado um modelo de duas temperaturas.Por fim, foi realizada uma busca usando um algoritmo de Monte Carlo para estimar a distribuição posterior dos parâmetros livres. Esta abordagem permite contabilizar adequadamente as múltiplas contribuições de primeira ordem, as suas correlações e uma melhor compreensão do espaço paramétrico.A partir do modelo de Boltzmann, pudemos concluir que a termalização e-e é rápida, o que valida a hipótese usada no modelo de duas temperaturas de que o equilibrio e-e é estabelecido instantaneamente. Encontraram-se correlações entre os parâmetros do modelo de duas temperaturas, que mostram que um parâmetro de acoplamento e-i constante pode ser uma suposição eficaz numa gama de parâmetros ampla, se tal constante for ajustada para a intensidade do "pumping". Uma correlação positiva foi encontrada entre ε_t e δ_s/δ_0 e correlações negativas prevalecem entre δ_s/δ_0 e G_ei/G_ei^0 e m_eff/m_eff^0. Em geral, um modelo semelhante a um gás de eletrões livre e o modelo de duas temperaturas parecem descrever bem os dados. Os valores de G_ei aumentam com a temperatura eletrónica, no domínio que sondamos, mas mantiveram-se na faixa dos valores publicados anteriormente.

Constraining the Axion-Photon Coupling Using Subgiant Asteroseismology
2022-11-29 15:00 - 17:00 | Sala de Formação Avançada, Piso 2, Pavilhão de Física, Campus da Alameda
Asterosismologia tem-se revelado, juntamente com modelização estelar, uma ferramenta indispensável para constringir propriedades de matéria escura. Neste trabalho, estudamos pela primeira vez a influência de produção axiónica na evolução de uma estrela subgigante -- {KIC} 6933899 -- comparando modelos computacionais com dados observacionais, de forma a limitar o acoplamento $g_{a\gamma}$. Executamos primeiro uma calibração de alta precisão de um modelo estelar, de modo a obter uma referência para os testes subsequentes. Aplicamos seguidamente um diagnóstico de duas fases, primeiro utilizando quantidades globais e seguidamente rácios sísmicos de alta precisão. Concluímos que a presença de axiões não contraria observações, pelo contrário melhorando a qualidade dos modelos estelares para uma certa gama de acoplamentos. Adicionalmente, concluímos que sismologia permite a definição de um limite superior a $g_{a\gamma} \leq 6.4\times 10^{-11} $ GeV$^{-1}$, compatível com observações a um nível de confiança de $68\%$, mais estrito que os constrangimentos mais recentes derivados tanto de observações a aglomerados globulares como de detecções diretas. Sugerimos adicionalmente um limite mais conservador de $g_{a\gamma} \leq 1.1\times 10^{-10} $ GeV$^{-1}$ com um intervalo de confiança de $95\%$. Ademais, este novo método de diagnóstico tem a possibilidade de vir a ser aplicado a dados que serão obtidos através de futuras missões asterosismológicas, como é o caso da {PLATO}, projetada para ser lançada em 2026, na perspetiva de expandir o nosso conhecimento sobre axiões.

Black Hole Fusion in Alternative Theories of Gravity
2022-11-29 17:00 - 19:00 | Anfiteatro PA1, Piso -1 - Pavilhão de Matemática, Campus da Alameda
ResumoNeste trabalho são estudadas duas teorias alternativas da gravidade do ponto de vista do processo de fusão dos horizontes de dois buracos negros. Numa primeira fase a gravidade escalar-tensor-vector é considerada. Começamos por apresentar um resumo da teoria, seguido da descrição da fusão, feita com o traçar das trajectórias dos raios de luz que definem o horizonte de eventos. Esta descrição evita recorrer a grande poder computacional ao usar o método da razão extrema de massas, no qual um dos buracos negros é considerado infinitamente maior que o outro. Os parâmetros relevantes que descrevem a fusão são então calculados, designadamente a duração do processo, a diferença na área do horizonte pequeno, e a taxa de crescimento da largura da garganta da fusão.Após isto, um estudo da gravidade cúbica Einsteiniana é levado a cabo. Como em gravidade escalar-tensor-vector, um resumo da teoria é apresentado, seguido de uma descrição da fusão e determinação dos parâmetros de fusão relevantes, e é estabelecida a relação entre o parâmetro de acoplamento no lagrangiano, Õ, e a intensidade dos efeitos gravíticos considerados. O estudo é extendido para regimes do valor de Õ mais abrangentes do que aqueles contemplados até agora na literatura.Por fim, após explorar os efeitos repulsivos do buraco negro pequeno em ambas as teorias, as condições que determinam o comportamento atractivo e repulsivo em ambas as teorias são unificadas de maneira a serem aplicáveis à fusão de todos os buracos negros esfericamente simétricos descritos por uma métrica semelhante à de Schwarzschild.

Extinction curves of type Ia supernovae from the Dark Energy Survey
2022-11-30 10:30 - 12:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
OnlineResumoPropomo-nos a analisar os parâmetros de poeira em supernovas do tipo Ia a partir de um conjunto de dados de 207 supernovas recolhidos pelo Dark Energy Survey (DES).Propomo-nos a criar uma metodologia de ajuste realizando primeiro testes com curvas de luz de supernovas simuladas.Fazemos ajustes às curvas de luz dos dados do DES, recolhendo valores de sBV (stretch de cor), Bmax (magnitude na banda B no máximo), Tmax tempo de máximo na banda B, E(B-V) e Rv de cada uma das supernovas da base de dados. Descobrimos que Rv é um parâmetro difícil de constrangir com uso exclusivo de ajustes de dados.Encontramos uma relação exponencial entre o Rv e o E(B-V) semelhante a relações encontradas na literatura, embora não consigamos quantificá-la satisfatoriamente nos nossos dados com um ajuste linear nem com com um ajuste exponencial.Descobrimos que o Rv mediano dos nossos dados está abaixo do Rv mediano da Via Láctea e que a distribuição de Av dos nossos dados segue uma exponencial, novamente em concordância com estudos anteriores.Comparamos os parâmetros de poeira das supernovas no nosso conjunto de dados com os parâmetros das suas galáxias de origem.Encontramos evidências para a existência de múltiplas populações de Rv dentro do nosso conjunto de dados através de análise de distribuições cumulativas. Os nossos resultados são consistentes com previsões de variações de leis de extinção com a quantidade de extinção, massa da galáxia de origem, redshift e stretch.Tentamos estimar Rv através de análise de populações

Polarization patterns in the sky and their influence in astronomical observations
2022-11-30 15:00 - 17:00 | Anfiteatro QA, Piso 1, Pavilhão de Química - Campus da Alameda
Resumo:As condições perfeitas para uma observação astronómica incluem um céu livre de contaminação luminosa. A contaminação luminosa é mais significatica em observações na banda do visível e pode tornar-se uma fonte de erros sistemáticos em observações polarimétricas. A Lua é o nosso objecto de estudo sendo a maior fonte de luz natural no céu noturno.De forma a compreender melhor como os padrões de polarização do céu devido a poluição luminosa afectam observações polarimétricas, este projecto tem como objectivo compreender construir um modelo que permita uma boa estimativa destes valores. O modelo considera a luz do luar que chega à atmosfera, foi originalmente radiação solar refletida na luaa, interage com as patículas atmosféricas e dispersa-se. Este fenómenos causa a padrões de polarização no céu que dependem principalmente da distância angular entre o alvo de observação e a Lua.Dependendo da localização do observatório, período e condições de observação, o modelo estima as características de polarização do céu, simulando os processos de dispersão com base na composição e densidade da atmosfera e comprimento de onda da luz incidente. Resultando na otimização de futuros planos de observação.Neste estudo, dois modelos analíticos são comparados. Adicionalmente, com as observações feitas com o FORS2 no observatório ESO-VLT no Paranal durante duas noites, observa-se uma excelente compatibilidade do modelo de Rayleigh com os dados observados. No entanto, o modelo começa a falhar quando não há condições ideais de observação e também para comprimentos de onda maiores. O modelo baseado em dispersão múltipla e outras correções são necessários para obter resultados mais precisos em determinadas condições. Adicionalmente, outras hipóteses foram tidas em consideração, como a dependência do comprimento de onda do grau de polarização ou do fator de despolarização.O modelo construído para os padões de polarização do céu noturno ajudará a planear observações futuras e corrigir a polarização de fundo em observações palarimétricas que usem o VLT.

Improved gas transport of polyurethane-based membranes for blood oxygenation
2022-11-30 15:30 - 17:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Extracorporeal Membrane Oxygenation (ECMO) is essential in critical care for themanagement of severe respiratory and cardiac failure. Considered the most importantpart of the ECMO circuit, the membrane blood oxygenator (BO) is responsible formaintaining O2 and CO2 levels in the blood. Current BOs require large membranesurface areas, but these have poor hemocompatibility, which leads to activation of thecoagulation system. Despite the considerable progress during the last decades incomponent technology and at the circuit level, a BO capable of performing efficientlyin prolonged ECMO does not exist. To improve the O2 permeability our research hasbeen focused on the development of new blend polyurethane-based (PUR)membranes, using polyether and polyester-based segmented PURs, which exhibitenhanced hemocompatibility, in association with a good flex-life and mechanicalstrength..

Particle reconstruction in large liquid scintillator detectors using charge and time signal modelization - the SNO+ Neutrino Physics Experiment
2022-11-30 15:45 - 17:00 | Online
ResumoNesta tese elaboramos um modelo numérico para prever o tempo e carga de sinais em detectores de cintilador líquido de grande volume.Descrevemos, em particular para SNO+, o fundamento físico da propagação de luz em tais detectores e combinamos essa descrição com a discretização das variáveis físicas usadas para descrever o modelo. Para implementar o modelo computacionalmente, várias optimizações, incluindo aproximações, são apresentadas e aplicadas ao algoritmo.Os resultados em tempo e carga obtidos através deste modelo são comparados com resultados de referência obtidos com a simulação Monte Carlo usada na experiência SNO+, e os resultados são discutidos no que toca à sua compatibilidade com os de referência e quanto à sua capacidade para informar sobre ajustes do algoritmo de modelização ou para optimizar o código. Um algoritmo de reconstrução baseado numa função de verosimilhança é introduzido e adaptado tendo em conta as características dos resultados do modelo.Finalmente, sumarizamos as vantagens e desvantagens do modelo numérico e propomos formas de as aproveitar e contornar, respectivamente. Discutimos também possibilidades de trabalho futuro na forma de melhorias ao modelo e ajustes aos parâmetros utilizados.Esta tese foca-se no caso particular do detector SNO+, mas o modelo pode ser aplicado prontamente a outros detectores de cintilação de grande volume. Optimizações que dependam da simetria esférica do detector SNO+ não podem ser aplicadas directamente a outros detectores, mas em tais casos outras simetrias, frequentemente cúbicas, existem e os mesmos métodos podem ser aplicados.

Production of single-cycle laser pulses through nonlinear pulse compression
2022-11-30 16:00 - 18:00 | Anfiteatro EA3, Piso 1, Torre Norte - Campus da Alameda
Atualmente, a maioria dos lasers ultracurtos são capazes de produzir impulsos com durações na ordem dos femtossegundos, com recurso a osciladores de Ti:Sapphire.Estes impulsos ultracurtos são a ferramenta ideal para explorar a dinâmica dos eletrões em átomos, sólidos e nanoestruturas. Como a resolução temporal está limitada pela duração do impulso, alcançar impulsos mais curtos permite-nos explorar os processos inacessíveis até então. Estes impulsos podem existir na forma de impulsos isolados de atossegundos, produzidos por lasers de impulsos com poucos ciclos óticos num processo de geração de altas harmónicas, permitindo assim o desenvolvimento de ferramentas de diagnóstico como difração de raios-x nos atossegundos ou espetrómetros de pequenas dimensões.Para obtermos impulsos laser de uma ou poucas oscilações, criámos, no laboratório VOXEL (GoLP/IPFN, Instituto Superior Técnico), um sistema de pós-compressão. A nossa instalação consiste num laser comercial (40 fs, 800 nm, 3mJ, 1kHz) cujos impulsos são focados numa fibra oca com um diâmetro interno de que está sujeita a uma pressão diferencial de Árgon. O impulso, que à saída da fibra possui uma maior largura espetral, é re-colimado antes de ser comprimido e analisado no tempo por um sistema D-Scan da empresa Sphere Ultrafast Photonics. Alguns mW de energia são amostrados para compressão e análise. Atingimos impulsos com menos de 4 fs com pouca dispersão do atraso do grupo (GDD) e uma transmissão de 33%. Esta configuração constitui uma ferramenta poderosa para a geração de impulsos laser de um ciclo único no laboratório, estando este agora equipado para produzir impulsos isolados de atossegundos com frequências na gama mais alta de ultravioletas através de um processo de geração de altas harmónicas.Fizemos também um estudo no Laboratoire d'Optique Apliquée (LOA), no Institut Polytechnique de Paris, onde dois métodos estado-da-arte da pós-compressão foram estudados. Apresentamos também uma conclusão sobre o método mais apropriado para cada situação.

Looking for coherence effects in the Quark-Gluon Plasma
2022-11-30 17:00 - 19:00 | Online
ResumoO observável jet pull fornece informação relativamente ao fluxo de cor estabelecido entre dois jatos inter-conectados, adicionalmente à habitualmente obtida através do momento e do tamanho dos jatos. Apesar das correlações de cor já terem sido estudadas anteriormente, propomo-nos desenvolver uma nova abordagem: aplicar o vetor jet pull em coerência intra-jato. Para tal, estudamos simulações de eventos protão-protão a energias de centro de massa semelhantes às do Large Hadron Collider: √s=5 TeV e √s=13 TeV. Nestes eventos definimos singletos e octetos de cor, através do duplo decaimento fraco de bosões e de eventos QCD, respetivamente. Definimos o observável pull angle num sistema di-jato formado através de técnicas de reconstrução anti-kT de jatos e de substrutura de jatos. O objetivo consiste em testar se os sinais relacionados com coerência de cor se mantém em ambiente de colisões de iões pesados. Ainda exploramos o decaimento do gluão num par c¯c, através de mesões D. Finalmente, adicionamos um background térmico aos três sistemas, tendo este características semelhantes às do background de uma colisão Pb-Pb a √s=5.02 TeV. O background provoca alterações significativas ao comportamento do singleto e do octeto c¯c. Dessa forma, aplicamos uma subtração de background ao nível dos constituintes, semelhante à utilizada nas experiências. Isto permite obter novamente a assinatura obtida em eventos pp em vácuo, provando que os efeitos de coerência de cor podem ser testados em colisões de iões pesados.

Impact of Quark-Gluon Plasma in Extensive Air Showers
2022-12-02 08:30 - 10:00 | Online
Resumo:Os raios cósmicos de ultra-alta energia interagem com a atmosfera terrestre produzindo cascatas atmosféricas de alta energia, cujos valores não são atingíveis nos aceleradores atuais, como no Large Hadron Collider (LHC). O número de muões na superfície da Terra é uma observável essencial para inferir a composição dos raios cósmicos. No entanto, os dados que têm sido recolhidos ao longo dos anos mostram que os modelos de interações hadrónicas utilizados para simular cascatas atmosféricas produzem um número de muões inferior àquele que se observa nas medidas experimentais. Este déficit é conhecido como o Puzzle Muónico e a sua origem deveria ser observável nas colisões de alta energia no LHC. De facto, experiências recentes de iões pesados revelaram a existência de um novo estado de matéria: o plasma de quarks e gluões, o qual tem sido estudado através de modelos de interações hadrónicas como o EPOS-LHC. Contudo, este revelou-se insuficiente e foi por isso modificado para explicar fenomenologicamente o déficit de muões observado, originando o modelo EPOS-QGP. O principal objetivo desta dissertação é estudar este novo modelo de forma a avaliar se o plasma de quarks e gluões consegue explicar tanto os dados obtidos no LHC como os dados provenientes dos raios cósmicos de ultra-alta energia.

High Temperature Superconductors Modelling
2022-12-02 14:30 - 16:00 | Anfiteatro QA1.3, Piso 1, Torre Sul - Campus da Alameda
Resumo: Supercondutores de alta temperatura (HTSc) podem conduzir densidades de corrente muito mais elevadas que condutores convencionais, sem as perdas associadas à resistência elétrica. HTSc têm temperaturas críticas maiores que 77K, que corresponde à temperatura de ebulição do azoto líquido à pressão ambiente. Processos de arrefecimento que usam azoto líquido são menos caros e menos complexos que os processos que usam hélio líquido. Consequentemente, HTSc são altamente vantajosos quando comparados com supercondutores convencionais para aplicações tecnológicas. Modelar sistemas com HTSc é essencial. Atualmente, os modelos usados baseiam-se numa lei de potências para a caraterística E-J. Esta lei é baseada em observações experimentais e é uma aproximação ao Modelo de Estado Crítico de Bean. A altamente não linear relação E-J resulta, por vezes, em computações numericamente instáveis e lentas. Neste trabalho, apresentamos um modelo para blocos de HTSc, o modelo densidade, que é derivável da teoria fenomenológica de Ginsburg-Landau para a supercondutividade. Este trabalho é desenvolvido sob a permissa de que a constante de Ginsburg-Landau tem um valor elevado e, também, sob a permissa de que a magnitude do campo magnético aplicado é elevada o suficiente para que a distância entre as linhas de fluxo seja muito menor que o comprimento de penetração, permitindo, assim, usar um modelo de campo médio. Para sistemas de YBCO e GdBCO com duas dimensões, as distribuições de campo magnético dentro dos blocos para os dois modelos estão em concordância na maioria dos casos. O modelo baseado na lei das potências tem sempre tempos de computação menores. No entanto, as simulações que usam o modelo da densidade apresentam sempre convergência e o mesmo não acontece para o modelo da lei das potências. Vários parâmetros são necessários para definir totalmente o modelo da densidade. O comprimento de coerência o comprimento de penetração e a constante de relaxação temporal são determinados por teorias microscópicas. Outros parâmetros, como a densidade de corrente de nucleação, são escolhidos heuristicamente. Estudámos o efeito de variar esses parâmetros nas distribuições finais de campo magnético.

Hacking the privacy amplification of quantum key distribution with machine learning, and countermeasures: An argument for considering classical side channels in quantum key distribution
2022-12-05 15:30 - 17:00 | Online
Resumo da tese:A distribuição quântica de chaves (QKD) explora os princípios da mecânica quântica para gerar e distribuir chaves privadas usando sistemas quânticos e um canal clássico público autenticado. Apesar de ser incondicionalmente segura, as suas implementações normalmente não o são devido a fontes de fuga de informação inesperadas, chamadas canais laterais. Espiões exploram estes canais laterais para obter informação sobre a chave privada. Canais laterais em QKD ou são semelhantes aos encontrados em implementações clássicas ou estão relacionados com o processamento quântico. Até agora, a investigação e o desenvolvimento na área têm vindo a negligenciar os primeiros.Nesta tese, revemos sumariamente os principais avanços na análise de segurança de QKD, os principais componentes das implementações e algoritmos de pós-processamento clássico e o uso de repetidores para aumentar a distância de transmissão. Também revemos de forma integral os principais ataques de canal lateral a implementações de QKD e as suas contramedidas.Propomos também um ataque de canal lateral clássico à etapa de amplificação de privacidade dum protocolo geral de QKD, usando técnicas de aprendizagem automática para analisar o seu consumo elétrico. Analisamos vários cenários simulados e conseguimos recuperar toda a chave privada múltiplas vezes. A máquina de gradient boosting foi o modelo com melhor performance em praticamente todos os cenários e recuperou toda a chave para taxas de amostragem do instrumento de medida suficientemente altas, independentemente do tamanho da matriz de hashing e do nível de ruído usados. Para modelos imperfeitos, formulamos uma estratégia, baseada na análise das matrizes de confusão do modelo, que pode viabilizar uma procura da chave por força bruta. Nas nossas abordagens de ataque, encontramos um trade-off entre o poder computacional necessário e a performance do ataque. Também discutimos contramedidas baseadas em inserção de ruído, masking e randomização. Algumas delas conseguem restaurar a segurança incondicional do protocolo de QKD.Este trabalho demonstra que técnicas de aprendizagem automática podem ser usadas para caraterizar canais laterais duma implementação de QKD de forma robusta e executar ataques poderosos.

Topological waves in two-dimensional plasmas
2022-12-05 16:00 - 18:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract In this work we compactify plasmas with two different types of electric fields applied and then find edge waves at the interface between magnetized domains.The first case is a local interaction caused by a Field-Effect Transistor; a second case, without a FET, with non-local Coulomb interactions stemming from all electronic density in the fluid is also addressed.Two distinct edge-modes are calculated for each case, their dispersion relation and velocity profiles.All four edge-modes are simulated in magnetized graphene with a hydrodynamic simulator.

Accretion disks around compact objects
2022-12-06 10:00 - 12:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Resumo:Um dos maiores desafios que enfrentamos em astrofísica é estudar buracos negros e compreender de que forma a relatividade geral os decreve adequadamente. Acredita-se que os candidatos a buracos negros sejam bem descritos pela solução de Kerr. Contudo, a evidenciência de matéria escura e o comportamento anómalo da gravidade no interior do horizonte de eventos levam-nos a considerar outras soluções de espaço-tempo conhecidas como \textit{black hole mimickers}. Algumas teorias sugerem que campos escalares bosónicos podem formar soluções compatas estáveis, dificeis de distinguir observavelmente de buracos negros, intituladas de estrelas dea bosões. Neste projeto, consideramos o seu limite para campos fracos, isto é, campos escalares muito leves ($\sim 10^{-17}eV$) acoplados de forma fraca com a gravidade, conhecido como estrela de bosões Newtoniana. O nosso objetivo é estudar se estas soluções podem reproduzir a acreção de um buraco negro de Kerr, sendo potenciais \textit{black hole mimickers}. Aplicando o modelo de Novikov-Thorne, descrevemos a acreção de um disco estacionário, fino, e opticamente denso. Comparamos o fluxo eletromagnético de discos em torno de buracos negros e de estrelas de bosões newtonianas, identificando assinaturas sobre a natureza do objecto acretante. Encontramos um espaço de parâmetros de massa e rotação do buraco negro tal que a luminosidade bolométrica dos discos é a mesma. Discutimos como o espectro de emissão dos discos na banda mais energética do ultravioleta pode ser usado para diferenciar as duas soluções de espaço-tempo. Por fim, verificamos se estrelas de bosões newtonianas descrevem as luminosidades de alguns centros galáticos ativos. Concluimos que estes que são consistentes com soluções compactas de campos escalares leves ($\sim 10^{-16} - 10^{-19} eV$).

Two-fluid models in solid state plasmas
2022-12-06 11:00 - 13:00 | Sala P9, 2 Piso, Pavilhão Matemática, Campus da Alameda
Desenvolvemos um modelo hidrodinâmico para o escoamento de quasi-partículas em grafeno bicamada no ponto de neutralidade, o qual implementamos numericamente acoplando a equação de Poisson. A partir do modelo teórico, caracterizamos a instabilidade de duas correntes eletrão-buraco quanto ao efeito da temperatura, velocidade inicial de deriva, campo magnético e colisões.Comprovamos a existência de um limiar de velocidade de deriva para criar instabilidades da ordem da velocidade térmica e uma velocidade de pico, após a qual a taxa de crescimento máxima satura. Neste estágio, o vetor de onda mais instável adquire uma componente perpendicular à velocidade inicial. Tanto a contribuição de um campo magnético externo como das colisões diminuem a taxa de crescimento, mas, sob parâmetros típicos, o seu papel só se torna aparente para modos de comprimento de onda muito longos.Confirma-se a possibilidade de relaxar a corrente somente através de mecanismos eletrostáticos no limite isotérmico, dando origem a uma condutividade longitudinal DC bem definida ∝T³/². Incluindo o espalhamento, dois regimes de transporte distintos, dominados respectivamente por processos eletrostáticos e colisões, são delimitados pela temperatura e pelo campo elétrico. A mesma análise da condutividade Hall revelou que as diferenças relativas ao regime linear não são tão marcantes. Finalmente, a inclusão do efeito do aquecimento Joule inibe o estabelecimento de um regime de saturação excluindo o espalhamento, e a adição desses termos, juntamente com a dissipação de calor pelos fonões para contrabalançar a potência dissipada por efeito de Joule, resulta num comportamento significativamente diferente da condutividade com a temperature

Testing the radiation resistance of CIGS solar cells for space applications
2022-12-06 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
As células solares CIGS são um candidato promissor para aplicações como fonte de energia em ambientes de radiação severa, devido à sua elevada eficiência de conversão e capacidade para manter níveis de rendimento adequados após sofrer danos induzidos pela radiação. Este trabalho pretendeu testar a resistência das células CIGS à radiação monitorizando os efeitos da irradiação com protões nas suas propriedades elétricas e estruturais e avaliando o impacto de tratamentos por aplicação de luz e corrente na recuperação de dispositivos irradiados.A caracterização J-V com luz após irradiação com protões de 1 MeV evidenciou a tendência de degradação do rendimento das células solares com fluências aplicadas desde 3.8×1012 H+/cm2 até 3.8×1013 H+/cm2, sendo que a redução da eficiência foi dominada por perdas na voltagem de circuito aberto. As medidas J-V no escuro revelaram um aumento da densidade de corrente de saturação e do fator de idealidade após a irradiação com fluências até 1×1014 H+/cm2, o que sugere que os danos provocados pela radiação introduziram defeitos no absorvedor CIGS que promovem recombinação do tipo Shockley-Read-Hall na região de espaço-carga e/ou nas fronteiras dos grãos. Durante um período de repouso no escuro e à temperatura ambiente, nenhuma recuperação significativa desses defeitos foi observada. Adicionalmente, medidas de difração de raios-X de ângulo rasante feitas em amostras virgens e irradiadas não mostraram quaisquer sinais de degradação da qualidade cristalina após a irradiação com protões.As metastabilidades observadas nas células CIGS aquando dos tratamentos por aplicação de luz e corrente foram interpretadas como sendo um fenómeno de fotocondutividade persistente que melhorou temporariamente as propriedades de recombinação em dispositivos virgens e irradiados. Ambos os tratamentos contribuíram, no longo prazo, para uma recuperação parcial das propriedades elétricas em dispositivos previamente irradiados.

Phase Control of Nonlinear Breit-Wheeler Pair Creation
2022-12-06 14:00 - 16:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Resumo: Plasmas eletrão-positrão existem na vizinhança de objetos astrofísicos, como estrelas de neutrões. Este é um dos motivos que contribui para o interesse geral em estudar os comportamentos destes plasmas, que contrastam fortemente com plasmas de laboratório convencionais ião-eletrão devido à simetria das massas entres as espécies positivas e negativas. A produção de pares eletrão-positrão em quantidade suficiente para observar efeitos coletivos é um desafio em física moderna. Uma maneira de gerar estes pares consiste em colidir um impulso de laser de alta intensidade com um feixe de eletrões relativista. Este esquema permite a produção de fotões de alta energia através da dispersão de Compton não linear, que posteriormente decaem num par eletrão-positrão através da criação de pares de Breit-Wheeler não linear. Uma desvantagem destas experiências atualmente reside no número baixo de positrões produzidos e na interferência com outros processos (como pares produzidos por fotões de bremsstrahlung). Nesta tese, um esquema usando um impulso de laser com duas cores é usado para alcançar a separação espacial dos pares produzidos na interação, e dos eletrões do feixe inicial. Um modelo teórico é introduzido para prever quando ocorre separação de momento das cargas em função dos parâmetros do impulso de duas cores (especialmente, da fase) e simulações Partícula-na-Célula mostram que este efeito dá origem a observáveis mensuráveis em experiências futuras. Simulações com largura de feixe finito mostram a separação física dos pares e a corrente produzida pelo movimento destas, que pode ser controlado variando a fase relativa entre as duas componentes do laser.

Searching for axions in α-Ori
2022-12-06 15:00 - 17:00 | Sala V1.05, Pavilhão de Civil, Piso 1, Campus da Alameda
Axiões são partículas hipotéticas que surgiram como solução para o problema de CP da CDQ, porém o seu potencial como partículas de matéria escura logo foi descoberto. Uma das possíveis formas de produção destas partículas é através do acoplamento com fotões sob a influência de campos eletromagnéticos intensos, tais como os que existem no núcleo das estrelas. Neste trabalho, exploramos este canal de perda de energia em estrelas massivas, nas quais é esperado um efeito mais significativo. Mais especificamente, calibramos a supergigante vermelha ɑ-Orionis, tendo em conta diferentes valores da constante que rege o acoplamento acima mencionado, com o objetivo de estabelecer um limite superior na mesma, tendo por base os efeitos desta interação na estrutura e evolução da estrela. Com base nesta análise, concluímos que a adição de perdas de energia associadas aos axiões dá origem a perfis distintos daqueles que não incluem matéria escura, especialmente nas regiões mais centrais, para as quais ondas de gravidade internas -- possivelmente detetadas no futuro -- devem configurar um bom diagnóstico. Finalmente, estabelecemos um limite superior na constante de acoplamento de a partir do qual não encontramos modelos capazes de reproduzir as características da Betelgeuse.

Proton Irradiation effects in h-BN nanomembranes
2022-12-06 16:00 - 18:00 | Sala E2, Torre Norte, Piso -1 - Campus da Alameda
Resumo:O h-BN é um semicondutor de hiato largo emergente. A sua excelente condutividade térmica, resistência mecânica e resistência à oxidação, aliadas à sua estrutura em camadas semelhante à da grafite tornam-no num material promissor para aplicações em nanoeletrónica bidimensional. Foram ainda descobertos emissores de fotões únicos entre os defeitos do h-BN, os quais são essenciais para diversas aplicações em comunicações quânticas.O objetivo desta tese é estudar o efeito da irradiação por protões em membranas exfoliadas de h-BN. São usadas diversas técnicas experimentais para avaliar as propriedades óticas e estruturais dos flocos e para determinar a sua resistência às irradiações.Os espectros de luminescência induzida por feixe de iões são dominados por uma banda larga na região UV, que também é observada por cátodo-luminescência, que é atribuída a impurezas de carbono. Foi observada a extinção desta banda com a fluência da irradiação. Esta emissão tem origem principalmente na superfície dos flocos, e não foi restaurada pelos recozimentos. Não foram encontrados novos níveis capturadores de eletrões por termoluminescência após as irradiações, e verificou-se também uma redução da luminescência emitida. As medidas de espectroscopia Raman sugerem que ocorre conversão do h-BN para a fase cúbica do BN para maiores concentrações de defeitos implantados. Nas medidas de difração de raios-X de alta resolução observou-se a formação de tensões nalgumas amostras irradiadas, onde o parâmetro de rede c aumentou. Estas tensões foram significativamente reduzidas pelos recozimentos.

Semi-device Independent Protocols for Quantum Key Distribution
2022-12-07 10:30 - 12:00 | Online
Resumo:Neste trabalho politopos de Bell e correlações quânticas foram estudadas para Distribuição de Chaves Quânticas de modo Semi-independente de Dispositivos (DCQ SID). Para atingir este objetivo, diferentes politopos de Bell foram explorados para encontrar novas desigualdades de Bell que demonstram potencial para comunicações quânticas. Neste trabalho é apresentada uma descrição por facets completa pela primeira vez dos politopos (6,3,2,2), (3,3,3,2) e (3,2,3,3) e uma descrição incompleta dos politopos (2,2,4,4), (3,3,2,4) e (4,3,3,2). Para cada desigualdade gerada, certas propriedades de interesse foram estudadas nomeadamente o limite quântico, a eficiência mínima para fechar a Lacuna da Deteção e uma estimativa da dimensão mínima necessária para atingir o limite quântico. A utilidade destas desigualdades para DCQ foi explorada assumindo que os estados quânticos partilhados entre a Alice, o Bob e a Eve têm uma dimensão máxima de d=4x4x4. Das desigualdades estudadas, I22441 e I[[2,2,3,3],[2,2,2]]2 demonstram os melhores resultados. Para I22441 a eficiência mínima para obter chaves secretas foi ηQKD = 0.920 e a taxa máxima de chaves secretas foi 1.979. Para I[[2,2,3,3],[2,2,2]]2 a eficiência mínima para obter chaves secretas foi ηQKD =0.912 e a taxa máxima de chaves secretas foi 1.284.

Optimization of the development of bacterial vaccines In silico prediction of protein–ligand interaction during downstream process development using molecular dynamics simulations
2022-12-07 10:30 - 12:00 | Online
Resumo: Devido ao aumento da resistência antimicrobiana, o campo das vacinas bacterianas está a ter um grande desenvolvimento recentemente. O aumento da potência e eficiência do computadores aumentou a utilização de modelos computacionais para a sua investigação. Para este projecto, será implementada uma metodologia para realizar simulações molecularas cromatográficas de troca iónica para lisozima, uma proteína conhecida na literature, e sepharose FF como a resina, para comparar parâmetros de interacção utilizando o formalismo de steric mass action. Isto será realizado pelo grupo de Downstream processing na Janssen Vaccines em estreita coordenação com os engenheiros da empresa de software de simulacoes moleculares Schrodinger. Em primeiro lugar, foram feitas simulações de 50 ns para 32 orientações da proteína. A fim de determinar quais destas estabilizaram ou atingiram o equilíbrio e depois podem ser utilizadas para avançar a fim de atingir o objectivo, os dados da simulação foram primeiro examinados utilizando a energia de interacção proteína-superfície e a distância do centro da massa, a partir daí algumas das orientações foram removidas.Finalmente, foram criados mapas de distância para estimar os dois parâmetros de steric mass action: characteristic charge e steric hindrance factor para todas as restantes orientações, utilizando duas distâncias de corte para verificar a dependência da mesma. Os valores de characteristic charge obtidos foram 1.14±0.62 e 2.64±1.32, e os valores de steric hindrance factor foram 48.91±9.30 e 48.42±7.81. Os resultados e uma estratégia para obter a constante de equilíbrio foram discutidos em detalhe.

Distributed Quantum Annealing
2022-12-07 13:00 - 15:00 | Online
Resumo:Conseguem ser avistadas no horizonte as vantagens prometidas por computação quântica. No entanto, essas vantagens são mantidas longe devido a obstáculos como o ruído e a decoerência. Esses obstáculos limitam severamente a escalabilidade de computadores quânticos, mas uma das maneiras de enfrentar o problema poderá ser através da distribuição da computação quântica onde, idealmente, poderíamos aumentar os recursos computacionais apenas adicionando nodos ao cluster de computadores quânticos. Neste projecto é proposto um novo método para distribuir quantum annealing. A nossa abordagem depende do processo de Trotterização para dividir a evolução adiabática em passos locais e não-locais, cujos últimos são distribuídos usando operações locais e comunicações clássicas assistidas de entrelaçamento quântico (eLOCC). São estabelecidos limites teóricos no tamanho do passo do processo de Trotterização e na probabilidade da distribuição bem sucedida. Estes podem ser usados para extrair a utilidade do protocolo de quantum annealing distribuído partindo de um problema de quantum annealing. Estes limites são validados através de simulações numéricas da evolução do sistema, para uma gama de problemas de quantum annealing com complexidade crescente. As simulações revelam que este processo tem uma transição de fase many-body localization (MBL), que é semelhante a transições de fase encontradas em sistemas de Floquet. As simulações mostram também que o protocolo permite algumas falhas na distribuição. Finalmente, concluímos discutindo a viabilidade de quantum annealing distribuído considerando o progresso no estado da arte, aplicando os limites teóricos que foram deduzidos.

Higher gauge theory and its connections
2022-12-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The aim of the talk is to introduce some notions of higher gauge theory for a physics audience. Higher gauge theory is a generalization of standard gauge theory, where everything is raised one (or more) dimensions, e.g. the gauge potentials become anti-symmetric 2-index tensors, and the field strengths become antisymmetric 3-index tensors.The geometric language of differential forms provides a useful framework for describing higher gauge theory. The connections in the title refer both to the mathematical term for gauge potentials and to links with notions more familiar to physicists, such as monopoles, the standard model, Wilson loops etc.

Gravitational Footprints of the A4-symmetric Three-Higgs-Doublet Model
2022-12-07 16:00 - 18:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Resumo:Apesar dos seus vários sucessos, o Modelo Padrão de física de partículas deixa alguns problemas em aberto, nomeadamente a origem da assimetria bariónica do Universo e oscilações de neutrinos. Sabe-se por isso que a teoria está incompleta. Assim sendo, nas últimas décadas, várias extensões além do Modelo Padrão têm sido estudadas. Modelos com N dubletos de Higgs, tornaram-se populares por conterem ingredientes necessários para a bariogénese eletrofraca e mecanismo de seesaw. Dada a dificuldade em testá-las com as experiências existentes, fundos estocásticos de ondas gravitacionais provenientes de transições de fase cosmológicas têm vindo a ser investigados com uma nova abordagem de teste. Nesta tese, um modelo contendo três dubletos de Higgs com simetria A4 de sabor é estudado no contexto de fundos estocásticos de ondas gravitacionais. Considera-se o caso particular em que três dubletos adquirem um valor expectável no vácuo real. Relativamente a interações de Yukawa, associou-se a representação tripleto de A4 aos dubletos de SU(2)L, e diferentes representações singleto aos singletos de SU(2)L. Após construir-se o potencial efetivo a temperaturas finitas, implementou-se-o na ferramenta CosmoTransitions. Permitindo novos bosões com massas até 400 GeV, verificou-se que várias transições de fase de primeira ordem com acoplamentos abaixo de 4 originam espetros de ondas gravitacionais no alcance de sensibilidade de LISA, DECIGO e BBO. Constatou-se que bosões escalares mais pesados originam espetros com amplitudes pico maiores. Concretamente, verificou-se que estes espetros requerem pelo menos um bosão escalar com massa superior a 270-280 GeV, sendo assim, mais pesado que o bosão de Higgs.

Blockchain-based Smart Contracts Application for Energy Trading
2022-12-12 14:00 - 16:00 | Online
ResumoO mundo está longe de atingir os objetivos da Agenda 2030 para o Desenvolvimento Sustentável. O setor de energia é responsável por quase três quartos das emissões que causam as alterações climáticas, provando que, para atingir estes objetivos, é necessário implementar novas soluções neste setor. É imperativo reestruturar o setor energético para acomodar uma maior parcela de fontes de energia sustentáveis, especialmente no setor residencial, uma vez que é um dos maiores consumidores de eletricidade no mundo. Com a transição para as energias renováveis, um novo tipo de agentes que consomem energia, mas também conseguem produzir - os \textit{prosumers} - passam a ter um papel mais importante no mercado. Por isso, a estrutura tradicional centralizada do mercado não consegue suportar estes novos desafios. É crucial criar novos modelos de comercialização de energia, que sejam descentralizados, eficientes e seguros. Esta tese propõe o desenvolvimento de uma aplicação, utilizando a tecnologia \textit{blockchain}, que implementa contratos inteligentes que validam e auditam automaticamente as transações de energia. Isto contribuirá para o desenvolvimento de uma sociedade mais sustentável, favorecendo a redução do recurso a combustíveis fósseis como forma de produzir energia, tornando estes novos sistemas mais acessíveis e fiáveis. Além de contribuir drasticamente para a redução de emissões de carbono e aumento da eficiência energética, pode também ter impactos financeiros significativos, ao proteger o mercado de energia da instabilidade do mercado de combustíveis fósseis.

Twisting polarization, quasidisorder and Topological states
2022-12-14 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Mappings between liquid crystals and superconductors motivated interest on the effects of chiral molecules on the spin transport across aconducting electronic system and on the possible influence of topological states.Theinterplay between an incommensurate potential andtopological states is alsodiscussed, in the context ofa superconductor.

Using numerical relativity to search for physics beyond the Standard Model in gravitationalwave observations: high-mass LIGO-Virgo events as boson-star mergers
2022-12-15 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Gravitational-wave astronomy has delivered dramatic leaps forward in our understanding of gravity, astrophysics and our Universe at large. Despite this success, we are yet to find evidence for one of the holy grails for current scientific research: physics beyond General Relativity (GR) and Standard Model of Particle Physics (SM). To this end, ultra-light bosons are not only one of the simplest extensions of the SM but are also widely considered good candidates to build up part of Dark Matter. For this reason, important efforts are being dedicated towards searching for these particles and, specifically, for the impact of boson clouds on black-holes. In this talk I will discuss an alternative strategy to look for these particles. In particular, I will present the first systematic comparison, within the framework of Bayesian inference, of LIGO-Virgo events to a signal model for a specific type of object beyond the SM, namely a set of nearly 1000 numerical simulations of mergers of exotic objects known as (vector) boson-stars: self-gravitating condensates of ultralight bosons. I will discuss the chances that a fraction of the underlying population of these events correspond to boson-star mergers instead of black-hole ones, providing estimates of the mass of the corresponding ultralight boson. If time permits, I will also discuss the effect of the quantum properties of boson-stars in their gravitational emission and the consequence of its inclusion in parameter inference and model selection.

Advanced Imaging with Extreme Ultraviolet and Soft X-rays
2022-12-16 09:00 - 11:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Extreme Ultraviolet radiation (EUV) from high harmonic generation (HHG) results in ultrashort coherent pulses of 10's nm wavelength. Their duration, down to the attosecond range, allows probing ultrafast processes, while their degree of coherence at short wavelength allows coherent diffractive imaging techniques to be implemented with resolutions reaching the wavelength range. However, due to low reflectivity and being highly absorbed by most materials, there's still the need to improve EUV imaging methods.In this work, we explored novel EUV HHG Imaging techniques, including the characterization of Lithium Fluoride detectors, generation of vortex beams and imaging with Spiral Zone Plates, a very promising phase contrast method.

Dia do DF
2022-12-16 16:00 - 19:00 | Academia das Ciências de Lisboa

Quantum Computing applied to Partial Differential Equations in Plasma Physics
2022-12-19 09:00 - 11:00 | Online
Abstract:Quantum computers are a promising tool to solve certain problems that are out of reach of classical computers. In this presentation, I propose new quantum algorithms for solving some nonlinear partial differential equations, which occur frequently in the context of plasma physics. I start by presenting new classical methods with better asymptotic complexity, and then prove that, when compared with the classical case, this new quantum algorithm shows an exponential speedup with regards to the number of time steps considered, while also having a quadratic speedup in other parameters. Additionally, I also propose a new techniques to perform quantum error correction and to study quantum many-body systems.

Hybrid Quantum-Classical High-Performance Computation
2022-12-19 14:00 - 16:00 | Online
Abstract:Quantum computing enjoys some proven computational advantage over classical computers, with alluring applications: e.g., quantum system simulation, quantum chemistry, cryptography, machine learning. However, current implementations of quantum computers are still far from resilient to effects such as dephasing and decoherence, putting them in stark contrast to the classical computing technology developed over the last century. We would like to make use of both these aspects (quantum computational power and classical computing technology), thus motivating the seek for hybrid algorithms: those that combine the two types of computation. But, this raises the question: when limiting, for example, the maximum coherent depth to the quantum circuits used, is any quantum advantage preserved? If so, how much, and in to what relation to the limits imposed? We analyze this question from a more tractable perspective, namely, by modelling such a limitation as a limitation on the number of calls made coherently to an oracle of the problem. We establish an interpolation regime for a particular problem (that of Eigenvalue Estimation) as a generalization of existing results in the literature,and by applying a recently developed technique, named Quantum Singular Value Transformation. We then look at prospective following results, by inspecting the classes of problems for which the maximum quantum speedup is known (but an interpolating regime is not).

Entangled Photon Pair Source for Free-Space Quantum Communication
2022-12-19 19:00 - 21:00 | Online
ResumoInformação é um dos recursos mais valiosos do mundo e a informação quântica visa trazer um novo paradigma. Um dos ingredientes essenciais para as tecnologias de fotónica quântica, em particular comunicações quânticas seguras, são fontes de pares de fotões entrelaçados. O entrelaçamento quântico é uma propriedade particular dos sistemas quânticos que permite a implementação de comunicações seguras que de outra forma seriam impossíveis com informação clássica. Uma fonte de pares de fotões entrelaçados pode ser usada adicionalmente como Heralded Single Photon Source (HSPS) para experiências ópticas de Distribuição de Chaves Quânticas (DCQ). Nesta tese, desenvolvemos uma fonte de pares de fotões para telecomunicações em espaço livre capaz de produzir estados quânticos de alta qualidade. Para gerar entrelaçamento quântico, usámos um processo óptico não linear chamado Spontaneous Parametric Down Conversion (SPDC), que gera pares de fotões correlacionados. Caracterizamos estes pares usando um interferômetro Hong-Ou-Mandel (HOM) para medir e compensar o seu atraso temporal. Também usámos o Bell State Analyzer para medir a qualidade do entrelaçamento. Em adição, desenvolvemos um design preliminar para um emissor de estados quânticos ótico miniaturizado que serve como base para o design do primeiro nano satélite português para comunicações quânticas.

Quantum matter and its splendor: when plasmas, particles and quantum technologies meet
2023-01-12 16:00 - 17:00 | TBA
Abstract: Quantum Matter commonly refers to materials which require quantum mechanics for a proper description, and its study falls mainly in the field of condensed matter. Motivated by the interdisciplinarity in the most recent challenges of modern physics – namely topology, plasmonics, quantum technologies and dark matter – quantum matter requires different tools and covers subjects of various disciplines: plasma physics, material science and particle physics. This is why the best theoretical physics institutes across the world strongly invest on quantum matter research.In this talk, I will explain my research in quantum matter, which, in a nutshell, comprises the study of quantum materials under the view of a plasma physicist (and vice versa). In particular, I will present three axes of research that put in evidence such a rich, interdisciplinary merging of disciplines: graphene plasmonics, production and detection of axions (one of the best candidates to dark matter) in plasmas and meta-materials, and quantum simulations with cold atoms. I will conclude with a consideration on how my theoretical work is in close relation to the experiments performed both at IST and in other institutions.

The Thermodynamics of Quantum Computers
2023-01-18 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Exploiting quantum dynamics and quantum correlations to process information has established new forms of computation and simulation, offering significant speed-ups in the time of the computations. However, another potential advantage of quantum dynamics, still poorly explored, is the energetic performance of the computations, currently a bottleneck in classical high-performance computing. In this seminar, I will discuss some recent results we have obtained in the study of the thermodynamics of quantum gates, a physics of information problem currently getting increasing attention.

Symmetry Constrained Multi-Higgs Extensions of the Standard Model
2023-01-19 09:30 - 11:00 | Online

The high-energy collision of charged black holes
2023-01-19 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Ultra-relativistic collisions of black holes are ideal settings where to investigate how general relativity behaves under extreme conditions. A large fraction of the allowed parameter space has been explored over the past 13 years (including mass, spin, impact parameter), with the notable exception of charge. The inclusion of charge is significant because it adds non trivial degrees of freedom to the system. For example, charge constitutes another way to reach extremality (together with spin) and opens up a new channel to radiate away energy (through electromagnetic waves). Moreover, charge makes the study more directly relevant to particle physics and the production of microscopic black holes in cosmic rays and in particle accelerators. In this talk, I am going to present the first numerical-relativity simulations of head-on collisions of black holes with the same charge and mass. In particular, I am going to discuss what they can teach us about a variety of conjectures, including cosmic censorship and the role of the inner structure of bodies colliding at relativistic speed.

Extreme plasma physics in the lab and in astrophysics
2023-01-25 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Many extreme astrophysical scenarios share common underlying microphysics with laboratory scenarios with relativistic particle beams and ultra-intense lasers. In these conditions, collective plasma effects driven by relativistic flows, ultra-high field intensities, and quantum electrodynamics effects are intertwined. In many scenarios, these relativistic and quantum effects can have direct consequences on the collective plasma dynamics. The underlying first principle mechanisms are highly nonlinear, and occur at scales far from the plasma or the object scales, making these processes intrinsically multi-scale, and thus requiring a combination of theory and large-scale numerical simulations. The conditions under which extreme plasma physics can be relevant will be discussed, along with the recent progress (from large-scale simulations of compact objects to multi-dimensional laser/beam plasma interactions), illustrating how ultra-intense electromagnetic fields approaching the critical Schwinger field impact the collective plasma dynamics. This interplay will be emphasized, and the main challenges and open questions will be presented.Work partially supported by the European Research Council (AdG InPairs).

Particle Physics Seminars I
2023-01-25 16:00 - 19:00 | QA1.1, south tower
Speaker: Liliana ApolinárioTitle: Unveiling the time structure of QCD jetsAbstract: Heavy-ion collisions are a unique laboratory to recreate the high energy and density conditions prevalent during the primordial moments of our Universe: the Quark-Gluon Plasma (QGP). This new state of matter is made of the elementary building blocks (quarks and gluons) of Quantum Chromodynamics (QCD), a key ingredient of the Particle Physics Standard Model. Unveiling the characteristics of the QGP allows us to ascertain the QCD's fundamental properties. This goal can be achieved in hadronic collisions through jets: spray of particles that result from the fragmentation of high-energy quarks and gluons produced concurrently with the collision. The fact that jets in proton-proton collisions are well understood has allowed us to successfully use them to extract the QGP's time-averaged properties. However, jets are evolving multi-scale objects that witness the entire space-time evolution of the system, making them unique tools for analysing the strong time dependence of the QGP properties. In this talk, I will present the most recent breakthroughs that unlocked time-differential methods for a full time-scan of the QGP at current colliders' energies.Speaker: Nuno LeonardoTitle: The LHC at the intensity frontierAbstract: The LHC is our most powerful tool to probe nature at the smallest scales and most fundamental level. The strategy is to accumulate large datasets at high energies to search for tiny signals. One such signal was revealed a decade ago, and resulted in the experimental confirmation of the last standard model particle. While no new particles beyond the standard model have been established so far, there is tantalising evidence of their presence in the data. Namely, a persistent and significant pattern of deviations from the theory predictions has been revealed, the so-called flavour anomalies. I’ll present the exploration of rare signals around the flavour sector that we’ll continue to pursue at the LHC and beyond. Such exploration encompasses direct and indirect searches for new physics, with both general-purpose and dedicated detectors. In this context, I’ll also introduce the most recent CERN experiment, that we have just installed at the LHC, with the goal of observing collider neutrinos for the first time, and probing the anomalies in lepton universality. The broader goal is that of exploring the unmatched physics potential of the LHC to the fullest extent and into the intensity frontier we are now entering.Speaker: João PenedoTitle: Piecing together the Flavour puzzleAbstract: Despite its repeated successes, the Standard Model is not the last word in our understanding of the subatomic world. The peculiarities that set neutrinos apart from other particles hint at Neutrino Physics as the most promising gateway to Physics Beyond the Standard Model (BSM). In an era of precision, neutrino masses and mixing are fundamental pieces in the broader puzzle of Flavour. From the theoretical and phenomenological viewpoint, one strives to find unified and testable descriptions of the known flavour patterns which address fundamental problems in Particle Physics -- e.g. the smallness and nature of neutrino masses, the nature of dark matter, the sources of matter-antimatter asymmetry and its absence in strong interactions. Such new Physics may justify tantalising anomalies in the data. The unprecedented sensitivities of upcoming experiments (e.g. DUNE, Belle and SHiP) will allow us to scrutinise these BSM scenarios and persistent deviations within the next decade.Speaker: Andreas TrautnerTitle: The Standard Model flavor puzzle and perspectives of a resolutionAbstract: With decades worth of data from high precision flavor experiments and robust confirmation at the LHC, addressing the Standard Model flavor puzzle is more pressing than ever. I will briefly, pedagogically introduce the puzzle then discuss my way to approach its resolution. This involves new mathematical techniques, for example, to understand the violation of matter-antimatter symmetry, as well as new model building extensions (including multi-Higgs models) to scrutinize experimental anomalies and the elementary structure of quarks, charged leptons and neutrinos. Most importantly, the dynamics of the flavor structure needs to be understood in order to reduce the number of necessary input parameters. This gives way to testable predictions not only at the LHC and future colliders but potentially also in the cosmological background radiation and high energy cosmic rays. Since all of this could be embedded in UV complete frameworks such as string theory, a correct model should reveal groundbreaking connections also to other important puzzles of modern particle physics such as the origin of neutrino masses, dark matter, or the unification of gauge interactions.

A novel magnetoresistive tactile soft-sensor, inspired by biological cilia
2023-01-27 10:00 - 12:00 | Online
Resumo: A sensação táctil é fulcral para a precisão da motricidade humana, e a implementação deste tipo de sensibilidade em robôs através do desenvolvimento de sensores tácteis é de elevada importância para que estas máquinas tenham sensações tácteis como as nossas. Os sensores de magnetoresistência por efeito de túnel (TMR) são bons candidatos a transdutores para este tipo de dispositivos, devido à sua elevada sensibilidade e potencial de miniaturização. Com o objectivo de produzir um sensor TMR altamente sensível que simultaneamente permita a deteção de campo magnético em várias direções, a otimização de junções TMR de alumina sem necessidade de recozimento térmico foi realizada, atingindo um rácio de TMR de 35%. Um die monolítico com sensibilidade 2D numa configuração em ponte de Wheatstone foi concebido e fabricado, tirando partido da dispensa de recozimento das junções TMR desenvolvidas. Adicionalmente, de modo a modularizar o sensor e corrigir algumas das suas não-idealidades, uma interface electrónica analógica foi desenvolvida, com a capacidade de ser facilmente integrada em plataformas robóticas. Foi concebido um sensor táctil inspirado na estrutura ciliar encontrada em certos seres biológicos, que consiste numa protuberância cilíndrica alongada fixa à superfície do sensor TMR 2D. Uma relação empírica foi encontrada para a resposta do sinal 2D em função da defleção e rotação do cílio. Diferentes configurações do sensor ciliar foram testadas relativamente à sua capacidade de detetar e resolver topografia em superfícies, sendo capaz de detetar estruturas com até 20 µm de altura. A implementação de um dispositivo com capacidade para medir a textura de superfícies poderá permitir a utilização de uma nova métrica da qualidade destes produtos, tanto em sistemas de apanha automática como em sistemas de controlo de qualidade na cadeia de abastecimento. Maçãs e morangos que apresentavam duas classes de qualidade (maduro ou podre) foram testados. A precisão da classificação, avaliada através de validação cruzada com 1 fruto, foi de 96% quando foram testadas maçãs classificadas com um classificador Bayes Gaussiano Ingénuo e 83% quando foram testadas maçãs classificadas com um algoritmo de Floresta Aleatória. Este desempenho está em linha com aquele que é observado noutros sistemas tácteis ou baseados em análise de imagem, demonstrando o potencial deste sensor para o controlo de qualidade na agricultura.

The Quantum Operators of Virtual Particles
2023-01-31 16:00 - 19:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:We show that virtual particles, despite being unobservable, can be described by quantum operators which can be interpreted under certain conditions as valid quantum states with interesting connections to quantum information. For virtual fermions, we prove that such states can be regarded as 2-qubit thermal states and study their entanglement. For spin-1 virtual bosons and virtual pairs of fermions, we find them to be associated to 4-qubit operators containing all the details of the interactions. Finally, we study how renormalization affects these results. These findings represent new connections between quantum field theory, quantum information and quantum thermodynamics.

Particle Physics Seminars II
2023-02-01 16:00 - 19:00 | VA4, Piso -1, Pavilhão de Engenharia Civil
Speaker: Ruben ConceiçãoTitle: Exploring the extreme energy UniverseAbstract: Ultra-high-energy cosmic rays (UHECRs) and very high-energy gamma rays are the highest-energy known particles and radiation, respectively. Their study allows us to probe some of the most extreme phenomena in our Universe and to investigate its fundamental physics properties. The Pierre Auger Observatory, with its upgrade, AugerPrime, and the future Southern Wide-field Gamma-ray Observatory, are two of the most ambitious astroparticle physics facilities in the world. In this talk, I will briefly discuss the technological challenges and physics opportunities connected with the study of these physics objects, which defy our understanding about acceleration mechanisms and particle interactions.Speaker: Catarina CosmeTitle: Glimpses of a physicist journey to the dark side of the UniverseAbstract: In this talk, I will introduce myself, give an overview of my academic path, and briefly discuss the main lines of investigation that I have pursued so far. I will pay special attention to the dynamics and phenomenology of non-thermal Dark Matter candidates, in both standard and non-standard cosmologies. Finally, I will give a taste of future projects I want to follow.Speaker: Luiz Vale SilvaTitle: Opportunities in a high-statistics era for flavor physics: novel predictions of the Standard Model and New Physics probesAbstract: Flavor physics plays a central role in particle physics: for instance, it led to the discovery of Charge-Parity (CP) violation. I discuss briefly the current and future status of the extraction of the CKM matrix elements in the Standard Model (SM). I also comment on the role charm physics can play in testing the Kobayashi-Maskawa mechanism, responsible for generating CP violation in the quark sector of the SM. Finally, I discuss bounds on different categories of generic New Physics contributions.Speaker: Cristóvão VilelaTitle: Neutrino experiments at the intensity and energy frontiersAbstract: Neutrinos are some of the least well understood particles in the Standard Model (SM) and play a central role in major open questions in Physics: How did matter come to dominate over antimatter in the history of the Universe? Are there symmetries underlying the flavour structure of the SM? Why are neutrino masses so small? In this talk I will briefly describe two neutrino experiments which will help elucidate these puzzles: DUNE, which is set to discover or rule out matter-antimatter asymmetry in neutrino oscillations; and SND@LHC, which will measure for the first time interactions of neutrinos of all three flavours produced at CERN's Large Hadron Collider.

8º Workshop do MEFT
2023-02-08 09:30 - 18:00 | Anfiteatro Abreu Faro
Convidamos toda a comunidade do Instituto Superior Técnico a participar na 8ª edição do Workshop dos alunos do mestrado de Engenharia Física Tecnológica. O objetivo do encontro é permitir a divulgação dos projetos que cada aluno irá realizar no âmbito da sua Dissertação de Mestrado.O encontro vai decorrer nos dias 8 e 9 de fevereiro de 2023, das 9h30 às 18h00h, no Anfiteatro Abreu Faro. O programa do workshop está disponível neste link.Este workshop é parte integrante da disciplina "Projeto Integrador de 2º Ciclo em Engenharia Física Tecnológica" do curso de mestrado de engenharia Física Tecnológica.Comité Científico:Ílidio LopesGonçalo FigueiraPatricia GonçalvesPedro RibeiroOrganização:Francisco PaisDiogo GonçalvesDuarte FeiteiraDavid LopesEufémio MarquesMaria GóisPaulo FigueiredoMiguel GonçalvesJoão Patrício

Search for new physics in exclusive processes at the Large Hadron Collider
2023-02-09 11:00 - 13:00 | Online
Abstract:Photon-photon collisions may provide the conditions to study particle production with masses at the electroweak scale. By tagging the leading proton from the hard interaction, the Precision Proton Spectrometer (PPS) provides an increased sensitivity to select exclusive processes and probe the standard model (SM). PPS is a detector system at approximately 210 m from the interaction point around the CMS detector, and it is designed to perform measurements of e.g. the quartic gauge couplings and search for rare exclusive processes. Since 2016, PPS has been taking data in normal high-luminosity proton-proton LHC collisions. A search for exclusive processes using data collected by the CMS experiment is performed and the results obtained are presented.

Axisymmetric critical collapse on a shoestring
2023-02-16 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: The study of vacuum critical collapse has acquired an aura of unapproachability in its 30 years of existence. It is often thought that only highly sophisticated numerical methods together with immense supercomputer clusters will suffice for treating this problem. My recently defended PhD thesis questions this folk lore by using only open-source code running on single machines to discover universal echoing in near-critical axisymmetric vacuum spacetimes. In this talk I will discuss my work from the software-development perspective. I will describe the approaches, tools, and techniques I used to make the most of the limited development manpower and computing resources available to me. Some of these, such as writing assembly code by hand in order to access vector capabilities of modern CPUs, come from my multimedia-software background and are not commonly encountered in physics codes.

Learning more from Kerr - New tools and related results
2023-02-23 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: There is good reason to think that gravitational wave physics, and particularly single black hole perturbation theory, is at a turning point. In this talk, I will review some of the challenges currently facing our understanding of single perturbed black holes. The setting of this review will be gravitational waves from the merger of stellar mass binary black holes (BBHs), and related conceptual tensions. I will pay particular attention to the relevance of Kerr “quasi-normal modes” (QNMs) to BBH merger, and I will discuss how our burgeoning understanding of QNM orthogonality points the way to new directions of research. As an example, I will present a proof-of-concept for a purely spectral method of solving Teukoslky’s radial equation.

Study of solar modulation effects on cosmic ray fluxes measured by the AMS experiment
2023-02-27 09:00 - 11:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
Resumo Ao atravessarem o sistema solar os raios cósmicos deparam-se com um fluxo de plasma magnetizado altamente condutor que emana do Sol, conhecido como Vento Solar, que transporta o turbulento campo magnético solar e com o qual estes interagem. Devido à atividade solar, a heliosfera está sujeita a variações de curta e longa duração que se refletem no fluxo de raios cósmicos na forma de variabilidade temporal, especialmente a baixas energias (até cerca de 50 GeV), na proximidade da Terra. Esta variabilidade da intensidade de raios cósmicos na heliosfera é conhecida como Modulação Solar dos Raios Cósmicos Galácticos. O Espectrómetro Magnético de Partículas Alfa (AMS-02) é um detetor de raios cósmicos de alta precisão instalado na Estação Espacial Internacional (ISS) que observa continuamente o fluxo de raios cósmicos e as suas variações no tempo, posicionando-se como uma plataforma única para estudar Modulação Solar. Nesta tese caracterizou-se de forma introdutória os raios cósmicos e relevou-se AMS enquanto o detetor usado para os observar e estudar. Estudou-se a estimativa do fluxo de raios cósmicos em grande detalhe enquanto se analisou o desempenho dos diferentes sub-detetores envolvidos. Descreveu-se o processo através do qual se utilizou a grande precisão de AMS e dos seus sub-detetores para identificar as astro-partículas que esta deteta e como foi estimado o fluxo resolvido em tempo com uma resolução de 27 dias (conhecida como rotação solar Bartel). Foi introduzido o processo físico da Modulação Solar e apresentou-se uma revisão da equação de transporte de Parker e as suas ligações ao campo magnético solar através dos parâmetros de propagação. Utilizando técnicas modernas de análise de frequências, caracterizou-se o fluxo de protões resolvido no tempo, quer no domínio do tempo quer das frequências, e correlacionouse o mesmo com as diferentes periodicidades temporais presentes no Ciclo de Atividade Solar. 2 Usando um modelo do transporte de raios cósmicos na heliosfera, em combinação com uma grande coleção de dados experimentais, mostrou-se evidência de um atraso temporal de 8 meses entre as observações do ciclo de atividade solar e o fluxo de raios cósmicos medido no espaço. Este resultado permite prever o fluxo de raios cósmicos na Terra através da observação da atividade solar.

Radiation Damage of Optical Components in Scintillator Detectors: from ATLAS/LHC Tile Calorimeter to Future Experiments
2023-02-27 14:00 - 16:00 | Online (Password Acesso Zoom: 412974)
Abstract:The European Strategy for Particle Physics update remarks on the importance of the detectors' R&D in preparation for the Future Circular Collider (FCC). In scintillator-based calorimeter systems, a high energy resolution is needed for an FCC electron-positron collider, while a hadron collider option requires high radiation hardness. The study of the degradation history of current operating detectors in actual experimental conditions, such as those of the ATLAS hadronic calorimeter TileCal, is fundamental in this context. In this work, a study of the ageing of the TileCal hadronic calorimeter due to radiation exposure is presented.In addition, a TileCal-like design will be proposed for an FCC electron-positron collider detector. Initial simulation studies on the design of this calorimeter, considering decisive factors such as the geometry, the sampling fraction and the energy resolution, were performed and will also be presented.

Vortices in two-dimensional condensates: towards a novel platform for quantum technologies
2023-02-27 15:30 - 17:00 | Online
Abstract: In this thesis, we consider the implementation of a quantum computer in systems of BoseEinstein condensates, quantum vortices and impurities as a roadmap to the investigation of the fundamental physics of these systems. We consider questions of structure, scalability, dynamical stability, robustness against decoherence/perturbations, amenability to external control and availability of quantum resources, which are necessary elements to encode and perform error-tolerant quantum information processing. BECs with vortices are a good platform to explore these questions, since it is well known that vortices in this superfluid are dynamically stable, topologically robust, stationary configurations that can be created in large numbers to form Abrikosov lattices. Their robustness, structure and scalability suggests the realization of qubits by making impurities occupy the vortex core. Thus, we began by characterizing these bound states to establish a good basis on which to encode a qubit. The next step was to characterize the excitations of the vortex-BEC. Motivated by questions of robustness, we introduced a measure that characterizes these excitations with respect to their interactions with any impurity. We found that some characteristic excitation modes of this system have an exceptional capacity to interact with impurities, which lead us to suggest a novel mechanism of quantum-level control of impurities. With this work, we have also established that the low-energy excitations of the vortex-BEC have an anomalous dispersion. We then studied the interactions between the two parts of the system, and found that the resulting collective excitations obey a deformed quantum statistics, known as para-Bose statistics. We characterized geometrically the single-body state of these excitations, known to be non-classical, and found a non-trivial geometric phase. In turn, the many-body states indicate that the excitations are in a condensed state. We attempt to characterize this condensate and discuss its implications towards this system as a quantum platform.

News (lots of them...) about the black holes and neutron stars in the galaxy
2023-02-28 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: The knowledge of compact stellar remnants, neutron stars and black holes, has greatly expanded in recent years. Many of the dogmas of the past were refuted and we face a new era in which the pieces of the puzzle are difficult to fit, but on the other hand many opportunities to contribute appear. I shall discuss in this seminar some of the latter, including the masses and mass distribution of both objects, their birth in stellar collapses and other events, and related topics.

Confinement in QED
2023-03-01 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
It is believed that in QCD its fundamental constituints are confined, i.e. that the Hilbertspace of the physics states does not include single quark or gluon states. How thisproperties translates into two point correlation functions is not clear. Certainly,positivity violation is an indication of confinement. Do we have other theories whereconfinement takes place? Indeed, this happens for the compact formulation on latticeof QED that has two phases: a confined and a non-confined phase. Then, how do theparticle propagators look like in each phase? What about positivity violation? In orderto help answering these questions, we revist the photon propagator for the puregauge theory. In the confined case we show that it has an associated linearly growingpotential, it has a mass gap, that is related to the presence of monopoles, and itsspectral function is not positive defined. In the non-confining phase, our simulationssuggest that a free field theory is recovered in the thermodynamic limit.

Topological magnons and quantum magnetism
2023-03-01 16:00 - 17:00 | PA1, Mathematics
Abstract: Investigations into the topology of band structures in solid state physics has been one of the most important conceptual and experimental enterprises in the physics of this century. In this talk I give a broad introduction to the state of the field. Then I shall focus on my own work on extending existing ideas into the realm of band structures of magnetic excitations and the connections with interesting open directions in quantum magnetism. I will say something about bulk probes of Dirac and Weyl magnons, surface probes of magnetism, the zoo of topological magnon states and the role of magnon interactions in shaping, destroying and creating nontrivial topology. I shall also connect these findings to transport and spectroscopic experiments on a variety of magnetic materials.

A next-generation gamma-ray observatory powered by machine learning techniques
2023-03-02 11:00 - 13:00 | Online (Password: [REDACTED]
Abstract:The Southern Wide-field Gamma-ray Observatory (SWGO) is the next-generation ground-based gamma-ray observatory to survey the Southern hemisphere sky. The experiment, currently in an R&D phase, is expected to have a large array of a few square kilometers composed of water Cherenkov detectors (WCDs) placed at a high altitude (4.4 km a.s.l. or higher) in South America. Such an ambitious project requires the design of a high-performance and cost-effective WCD to cope with the observatory needs, particularly the capability to identify shower muons, which is essential to ensure excellent gamma/hadron discrimination.In this work, it is shown that efficient muon tagging (and counting) can be achieved using water Cherenkov detectors with a reduced water volume and multiple PMTs, provided that the PMT signal spatial and time patterns are interpreted by an analysis based on Machine Learning (ML).The proposed WCDs would highly boost the physics capabilities of SWGO, enabling it to cover, with a wide field of view, a wide energy range, from low energies ($\sim$ 100 GeV) up to the PeV region.

Core collapse in massive ST theory: phenomenology and observational potential
2023-03-02 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Though General Relativity has been successfully tested so far, concepts such as dark energy and string theory suggest the need of modifying it. Scalar-tensor theory is one of the most popular alternatives discussed. We produce studies of stellar core collapse in spherical symmetry in which we systematically explore the parameter space that characterizes the progenitor stars, the equation of state and the scalar-tensor theory of the core collapse events. We identify a remarkably simple and straightforward classification scheme of the resulting collapse events. For any given set of parameters, the collapse leads to one of three end states, a weakly scalarized neutron star, a strongly scalarized neutron star or a black hole, possibly formed in multiple stages. The latter two end states can lead to strong gravitational-wave signals that may be detectable in present continuous-wave searches with ground-based detectors. The dispersive nature of the propagation of waves in the massive scalar field means the gravitational wave signals are long lived and many such signals can overlap to form a stochastic background. Using different models for the population of supernova events in the nearby universe, we compute predictions for the energy-density in the stochastic scalar-polarized gravitational wave background from core-collapse events in massive scalar-tensor gravity for theory parameters that facilitate strong scalarization.

Smart Colloidal Nanocrystals Towards Smart Electronics
2023-03-08 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Resumo:Smart colloidal nanocrystals, namely colloidal chalcogenides and halide perovskites, have recently received much attention due to their extraordinary properties, such as tunable, very sharp emission, faster carrier recombination, low-threshold lasing properties, and higher stability in ambient atmosphere. How do these properties change with different shapes, especially for two-dimensional systems, e.g., nanoplatelets? How the exciton behaves when they are assembled in solution? Also, how do they transport charge electronically inside smart devices in solo form or composite with MXene (unique 2D materials)? What about their photodetection limit in visible or near-IR? I will talk about these and what we reported in our recent work. Also, I will talk about future prospects in different electrochemical energy conversion applications of these materials.

Understanding precessing binaryblack-hole systems
2023-03-09 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT:Accurate signal models are essential in the analysis of gravitational wave events, from parameter estimation to astrophysical interpretation and tests of general relativity. As detectors get increasingly advanced it becomes ever more crucial to develop precision models of signals from a wide range of physical systems, including black-holebinaries where the spins are not aligned with the orbital angular momentum— precessing binaries. Evidence for a population of such systems has already been seen during the third observing run of the LVK and this is expected to become stronger in the upcoming run. I will discuss recent developments that have resulted in the first complete inspiral-mergerringdown model of the gravitational wave signal from a precessing binary where the precession effects have been tuned to numerical relativity through merger and ringdown as well as a more complete understanding of the phenomenology of such systems.

Perspectives on Beam-Driven Plasma-Based Acceleration
2023-03-13 11:00 - 13:00 | Room 4.41 (2nd floor, Civil Eng. Building)
Particle accelerators have been engines of discovery in our understanding of the Universe and have applications in many areas of modern life from medicine to security. The most powerful ones are 10’s of kilometers in length, determined by the strength of the accelerating electric field. It has been four decades since the concept of using a relativistic plasma wake for charged particle acceleration was first proposed. In relativistic plasma wakes the accelerating electric field can be orders of magnitude greater than in a conventional accelerator with the potential to reduce the size of the accelerating structure. The driver for producing such wakes can be in intense laser pulse or a high current charged-particle beam. During this time ingenious solutions for generating the ultra-high electric field over meter-scale distances, and generating and accelerating high quality electron and positron beams using such wakes have been realized. In this talk I will give a personal perspective on the progress of the field of plasma-based acceleration driven by ultrashort electron bunches and where it is headed

Effect of disorder on surface states of Weyl nodal loop semimetals
2023-03-15 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
We address the effect of disorder on the topological surface (“drumhead”) states of a Weyl nodal loop semimetal. Two types of disorder are considered: Anderson disorder breaks chiral symmetry, so, a topological index is not defined. Weak disorder produces the algebraic decay of the E=0 surface states into the bulk, and a broadening of the low energy density of surface states by degeneracy lifting. This behavior persists up to the bulk semimetal/metal transition at the critical disorder, Wc , above which all surface states hybridize with bulk states and become extended.Weak chiral disorder induces a diffusive metal at zero energy and, surprisingly, enhances the number of topological surface states as confirmed by the winding number and the low energy DOS of the open system. The topological surface states are exponentially localized into the bulk, and exhibit a multifractal structure on the surface. This is a novel topological metal hosting topological multifractal surface states. The number of surface states decreases either algebraically with disorder, or exponentially if the latter only affects intracell hoppings.

Piercing of a boson star by a black hole
2023-03-15 16:00 - 18:00 | Sala de Formação Avançada do DF - sala 2-8.11 - 2º Piso do Pavilhão de Física
Resumo: Dark matter is one of the biggest mysteries in physics. Could it be made of new light particles that form self-gravitating structures called boson stars? In this talk, I will explore what happens when a black hole collides with a boson star. Using numerical simulations in general relativity, I will show how the black hole swallows most of the boson star material and emits gravitational waves. I will also discuss the formation of a “gravitational atom” as a remnant of the collision. This talk will shed light on the nature and fate of these exotic objects in our universe.

Effective field theory of black hole perturbations with timelike scalar profile
2023-03-16 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: Many dark energy (DE) models are based on a scalar field with timelike gradient. If one hopes to learn something about scalar field DE from astrophysical black holes (BHs) then one needs to consider BH solutions with timelike scalar profiles. In this talk we begin with a review of the systematic construction of the effective field theory (EFT) describing perturbations around Minkowski and cosmological backgrounds with timelike scalar profiles. We then extend the EFT to arbitrary backgrounds. Finally, as an application of the general EFT, we study odd-parity perturbations around a spherically symmetric, static black hole background with a timelike scalar field responsible for DE.

Random matrix theory of open quantum systems
2023-03-22 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Describing interacting quantum systems in the presence of dissipation is a daunting task. One very fruitful approach to this problem, developed for unitary dynamics, is to represent the Hamiltonian of a generic system by a large random matrix. This approach eventually led to the development of the field of quantum chaos. Here, I will give an overview of the recent application of (non-Hermitian) random matrix theory to open quantum systems, where dissipation and decoherence coexist with unitary dynamics. I will discuss the spectral features, relaxation timescales, and steady states of three representative examples of increasing physical relevance: fully random Lindbladians and quantum maps, random open free fermions, and dissipative stronglyinteracting SYK models. Then, I will argue that complex spacing ratios are a powerful signature of dissipative quantum chaos, illustrating it with the case of boundary-driven spin-chain Lindbladians.

From III-Nitride nanowires to the fabrication of nano-structured piezoelectric transducers
2023-03-22 16:00 - 17:00 | PA1, Mathematics
Title: From III-Nitride nanowires to the fabrication of nano-structured piezoelectric transducersSpeaker: Dr. Noelle GogneauAbstract: The number of “Internet of Things” (IoTs) is constantly on a rise both in our daily life and in high-tech applications. Today, the question of their energetic autonomy is a key worldwide challenge. The recent miniaturization of electronic micro-devices, thus resulting in the reduction of their energy consumption to mW and even µW, combined with the progress in micro-nano-fabrication, have opened new perspectives to develop autonomous power systems based on the renewable energy harvesting. Among renewable energies, the mechanical deformations and vibrations, harvested using piezoelectric materials, present the advantages to be ubiquitous and permanently available.A new class of transducers has appeared these last years, integrating nanomaterials such as 1D-nanostructures. Thanks to their large surface-to-volume, high crystalline quality and nanoscale dimensions, semiconductor nanowires (NWs) present unique advantages to significantly enhance the piezo-device performances. The attention has turned to III-Nitride NWs thanks to their high-piezoelectric coefficients and their strong piezo-generation response [1,2].Here, we present the piezo-generation with Ga(In)N NWs going from the NW synthesis to the fabrication and testing of transducers. Our approach is based on systematic multiscale analyses. Starting from the characterization of the piezoelectric properties of unique NWs and the investigation of the piezo-mechanisms in play [3-5], we then demonstrate the high piezoelectric conversion properties of NWs on a device level [6-7].References[1] N. Gogneau et al. Phys. Status Solidi RRL 8, 414 (2014).[2] N. Jegenyes, N. Gogneau et al. Nanomaterials 8, 367 (2018).[3] N. Jamond, N. Gogneau et al. Nanoscale 9, 4610 (2017).[4] N. Gogneau, M. Tchernycheva et al. Semicond. Sci. Technol. 31, 103002 (2016).[5] N. Gogneau, P. Chrétien, T. Sodhi et al. Nanoscale, 14, 4965 (2022).[6] N. Jamond, N. Gogneau et al. Nanotechnology 27, 325403 (2016).[7] L. Lu, N. Gogneau, M. Tchernycheva et al Conference IEEE-NANO (2018).

Conditions for constraint preservation and gauge fixing in well posed theories: application to gravitation
2023-03-23 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: We use Partial Differential Equations (PDEs) to describe physical systems; in general, these equations include evolution and constraint equations. One method used to find solutions to these equations is the free-evolution approach, which consists in obtaining solutions of the entire system by solving only the evolution equations. Certainly, this is valid only when the chosen initial data satisfies the constraints, and the constraints are preserved in the evolution. In this talk, we will establish sufficient conditions for generic first order PDEs to guarantee the constraint preservation. For this purpose, we will discuss the strong hyperbolicity of the PDEs and their connection with the Kronecker decomposition of matrix pencils. Another method for finding solutions of PDEs with constraints is through extensions; some well-known examples are divergence cleaning for Electrodynamics and Z4 for Einstein equations. We will discuss how Kronecker decomposition suggests families of strongly hyperbolic extensions. Finally, we will discuss how this scheme can be extrapolated to PDEs that include Gauge freedom, providing a guide for fixing those freedoms in a well-posed way. We will show how these ideas apply to Einstein equations.

The Standard Model Higgs and the nature of gravity
2023-03-27 16:15 - 18:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract:The properties of the Higgs boson together with the absence of new physics at the Large Hadron Collider allow us to speculate about consistently extending the Standard Model all the way up to the Planck scale while staying in the perturbative regime. In this context, the SM Higgs non-minimally coupled to gravity could be responsible for the symmetry properties of the Universe at large scales and the generation of the primordial spectrum of temperature fluctuations seen in the Cosmic Microwave Background (CMB).In this work we show how Higgs-Inflation and its scale-invariant extension, known as Higgs-Dilaton inflation, can be embedded in Einstein-Cartan gravity.In particular we will discuss some phenomenological features emerging from the inflationary and post-inflationary dynamics.

Molecular Dynamics in Magnetic Fluids by 1H NMR - Paramagnetic Relaxation Enhancement and Local Order Fluctuations
2023-03-29 14:00 - 16:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
Abstract: NMR relaxometry is widely applied in the study of very diverse chemical systems, such as polymers, ionic liquids, liquid crystals and magnetic fluids. The molecular motions that characterize each system, occurring within timescales that range from picoseconds to milliseconds, are encoded in their relaxation dispersion profiles. Such motions generally include rotations/reorientations, as well as translational selfdiffusion, which should, in theory, be the necessary and sufficient contributions to explain the NMRD profiles of non-magnetic, isotropic systems. Regarding liquid crystalline phases, order fluctuations are usually the most effective relaxation mechanism, while for magnetic systems paramagnetic relaxation often dominates the NMR relaxometry profile. Recent works evidenced local order fluctuation dynamics in isotropic liquids, very far from the glass transition, either due to nano-segregation of polar-apolar domains, revealed by the X-ray profiles, or as a result of marked molecular anisometry. The present work mainly combines 1H NMR relaxometry and diffusometry with X-ray scattering experiments in the study of the molecular dynamics of magnetic and non-magnetic ionic liquids based on the [P6,6,6,14] + and [C8mim]+ cations and on PEG-based magnetic systems. The data obtained from all these three experimental techniques evidenced the need to consider either order parameter fluctuations or layer undulations in the NMRD model fitting analysis of these systems, despite their apparent isotropic nature. This observation indicates that NMR is sensitive both to the existence of local order, as well as to the characteristics of that order - orientational and positional. The electrical properties of the ionic liquids were additionally assessed via electrochemical impedance spectroscopy, being potentially interesting for dielectric applications, as relative permittivities of about 1000 were obtained.

Plasma in extreme conditions - creation and acceleration of electron-positron pairs with intense laser pulses
2023-03-29 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The next generation of lasers will access intensities above 10^23 W/cm^2. When plasmas or relativistic electron beams interact with these lasers, energy loss due to radiation emission, or quantum effects such as electron-positron pair creation become important for their dynamics. Repeated occurrence of pair creation can induce a socalled “QED cascade”, that generates an exponentially rising number of particles. This allows for creating exotic plasmas that are a mix of electrons, ions, positrons, energetic photons and intense background fields. Extreme laser-plasma interactions can be explored to form optical traps, create&accelerate particles and produce novel radiation sources. I will introduce a QED module coupled with the massively particlein-cell framework OSIRIS that allows studying nonlinear plasma dynamics in the transition from the classical to the quantum-dominated regime of interaction and discuss the possibilities for electron-positron pair creation and acceleration in nearfuture experiments.

Plasmas for Microelectronics Fabrication: A Modeling Perspective
2023-03-29 16:00 - 17:00 | PA1, Mathematics
Speaker: Prof. Mark Kushner, The University of MichiganTitle: Plasmas for Microelectronics Fabrication: A Modeling PerspectiveAbstract: The impressive advances in the capabilities of microelectronics logic and memory devices are largely due to plasma-based etching, deposition, cleaning, sputtering and passivation processes that have been translated to high volume manufacturing (HVM). Memory device architectures require etching high aspect ratio (HAR) features of only tens of nm diameter with aspect ratios exceeding 100. Logic devices now require removing or adding materials with atomic layer accuracy – atom layer etching (ALE) and atomic layer deposition (ALD). These manufacturing steps can now only be provided in HVM using plasma processes. Modeling and simulation (M&S) for both reactor and feature scale plasma processing has long served a supporting role. However, with HAR, ALE and HVM challenges at the forefront, M&S for plasma based device fabrication has received renewed attention to provide (or inspire) new equipment and process designs, and new insights. In this talk, the status of M&S for plasma processing will be surveyed. An overview and "quick-plasma" tutorial will first be provided, followed by a description of the numerical techniques used for reactor and feature scale modeling. Using examples from the speaker’s research group, the model-based scaling and optimization of plasma etching reactors will be discussed (e.g., multi-frequency, capacitively coupled plasmas for HAR etching and pulsed inductively coupled plasmas for front-end processing). The coupling of reactor-scale reactive fluxes to feature scale modeling of ALE and ALD, and HAR of ONO (oxide-nitride-oxide) stacks for high-density memory will be discussed, as well the role of machine learning for process design.*Work supported by the DOE Office of Fusion Energy Science, National Science Foundation, Lam Research Inc. and Samsung Electronics Co. Ltd.

Conformal Symmetry in the Standard Model and its Symbiosis with Gravity
2023-03-30 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: I will discuss how (broken) conformal symmetry can be used as a guiding principle to construct viable minimalistic extensions of the Standard Model. I will highlight the central role gravity (and its incarnations) plays in these considerations, with an emphasis on the EinsteinCartan formulation. I will show that an inflationary epoch driven by the Higgs field is automatically incorporated. Moreover, the inflationary predictions may in principle be related to the electroweak physics, thus creating an intricate link between the primordial and late Universe. Finally, I will comment on the self-consistency of these constructions.

Non-linear Electrodynamics derived from the Kaluza-Klein Theory
2023-04-06 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: The lagrangian of the Kaluza-Klein theory, in its simplest five-dimensional version, should include not only the scalar curvature R, but also the quadratic GaussBonnet invariant. The general lagrangian is computed and the resulting non-linear equations which genralize Maxwell's system in a quite unique way are investigated. The possibility of the existence of static solutions is presented, and the qualitative behaviour of such solutions is discussed.

Supermassive rotating boson stars in highly-asymmetric binaries: transient resonances and gravitational-wave observables
2023-04-12 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The historic detection of gravitational waves paved the way for precision gravitational-wave astrophysics to blossom at unprecedented proportions. The sensitivity increment of ground-based interferometers, as well as the arrival of next generation space-borne detectors, will unequivocally strengthen our understanding of the gravitational interaction in extreme conditions. In this talk, I will focus on one of the prime targets of LISA, the so-called extreme-mass-ratio inspirals (EMRIs). EMRIs are binaries that consist of a primary supermassive compact object, and a stellar-mass secondary companion. Even though we are currently performing pertinent tests to characterize the ``Kerrness'' of astrophysical compact objects that reside in galactic cores, environmental effects, quantum corrections and generally multipolar deformations can significantly affect the gravitational-wave emission from non-Kerr sources. In this talk, I will discuss the rich orbital and waveform phenomenology of EMRIs as well as potential observables of fascinating effects associated with transient resonances in non-Kerr black-hole mimickers and in particular supermassive rotating boson stars. Finally, I will briefly discuss the impact of exotic objects on the gravitational radiation emitted from such binaries, that may be distinguishable with future space-based detectors, in order to shed more light into the electromagnetic degeneracies that currently exist between black holes and exotic compact objects.

Exploding stars and catastrophic collisions
2023-04-13 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Supernovae and stellar collisions are the sometimes incredibly luminous, and sometimes not so luminous, deaths of stars that play a vital role in chemical enrichment, galaxy feedback mechanisms, and our understanding of stellar evolution. Type Ia supernovae, the explosions of white dwarfs in binary systems, are vital for constraining the cosmological parameters. In this talk, I will focus on the latest results on the progenitors and explosion mechanisms of Type Ia supernovae from the state-of-the-art transient survey, the Zwicky Transient Facility, and describe how their diversity may impact future precision measurements of dark energy. I will also highlight recent advances in the related area of stellar collisions, which are testing the boundaries of current theoretical models, as well as discuss the link to kilonovae from neutron-star mergers (with and without associated gravitational-wave detections).

Reaction mechanism for CO2-N2 low-temperature plasmas: the role played by O2 and N2 on the CO2 vibrational kinetics and dissociation
2023-04-14 15:30 - 17:00 | Online
Resumo Entre vários métodos atualmente em desenvolvimento para reduzir as emissões antropogénicas de CO2 de modo a reduzir os efeitos das alterações climáticas, a tecnologia de Captura e Utilização de Carbono (CCU) através plasmas não térmicos (NTPs) é bastante promissora. Descargas elétricas de CO2 são estudadas atualmente, tanto do ponto de vista experimental como de modelização, com o objetivo de compreender cinética do plasma e, idealmente, alcançar uma dissociação eficiente de CO2. Este trabalho contribui para este objetivo através de uma investigação teórica, experimental e de modelização da dissociação de CO2 em NTPs de CO2. Em colaboração com Laboratoire de Physique des Plasma (LPP), é feita uma caracterização experimental de uma descarga luminescente DC em misturas de CO2-N2 através espectroscopia de absorção de infravermelho por transformada de Fourier (FTIR) como diagnóstico principal. Paralelamente, foi desenvolvido um modelo autoconsistente 0D para descargas de CO2-N2 que inclui a cinética vibracional dos primeiros 72 níveis de CO2, 10 níveis de CO e 59 níveis de N2. Foi ainda realizado um refinamento da cinética química do oxigénio, motivado pela relevância das espécies de oxigénio na cinética do plasma de CO2, seguido de um estudo de diferentes misturas de CO2-O2 utilizando o código numérico Lisbon KInetics (LoKI). O papel desempenhado pelo nível eletronicamente excitado CO(a3Πr) em mecanismos de recombinação é responsável pelo efeito prejudicial da adição de O2 na descarga. Além disso, foi revelada a importância da troca vibracionaltranslacional (V-T) do CO2-O na descrição da cinética vibracional do CO2. A partir da comparação entre resultados da simulação e dados experimentalmente obtidos no LPP, este trabalho levou ao desenvolvimento de um “mecanismo de reação” (ou seja, um conjunto de reações e coeficientes validados experimentalmente). O efeito positivo da adição de N2 na dissociação de CO2 plasmas CO2- N2 é explicado pela diluição, limitando as reações de recombinação e pelo papel de nível N2(B3Πg) no aumento da conversão de CO2. Finalmente, é ainda observado que transferência de energia vibracionalvibracional (V-V) do CO2-N2 é crucial para uma descrição adequada da cinética vibracional do CO2.

Detection of small concentrations of molecules in the air with an artificial nose
2023-04-19 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Detection of target molecules in the air is an important task in many fields, from safety,to security, quality control, and even medicine. There are several types of such sensors, optimized to different target compounds andto different concentrations. An artificial nose, or e-nose, aims to mimic the nose of adog, which is known to detect and recognize great number of scents and is sensitive tominute concentrations. Ideally, an artificial nose would have one sensor per targetcompound, but clearly this is not the case as individual sensors can respond to severalmolecules. Instead, it is beneficial to use approaches of artificial intelligence to find"fingerprints" of particular scents. In the seminar, I will present our work on an e-nose that is based on capacitive sensorswith different functionalizations. Initially, the system was developed with the aim ofdetecting explosives, such as TNT and RDX. In the ongoing project, we are aiming atmodifying the system to detect cancer based on the exhaled air.

Collapsed structures in scalar-tensor theories of gravity
2023-04-19 16:00 - 18:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract:Dark energy represents perhaps the most relevant problem in cosmology. Light scalar fields coupled to matter could explain the accelerated expansion of the universe. This implies going beyond Lambda-CDM and the SM, yet there is no observation of such fifth forces in our solar system. This discrepancy can be resolved by a screening mechanism. From the plethora of theories, we are interested in studying the chameleon field. The presence of this fifth interaction during the radiation-dominated era of the universe would change the structure formation history, alleviating some of the current cosmological tensions. Moreover, the coupling of this field to compact objects, such as neutron stars or white dwarves, affects their structure, stability, and dynamics, providing us with some hints about its detectability.

Linear response of electrically K-mouflaged objects
2023-04-20 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In non-linear electromagnetism charges come equipped with a natural screening mechanism a la K-mouflage. In this talk I will briefly review this mechanism and discuss some phenomenological consequences of a model of dark matter interacting via dark photons. I will then discuss the linear response of screened charges in the context of Born-Infeld and ModMax theories. I will show how it is possible to construct ladder operators for the perturbations and how polarisability and susceptibility of certain series of multiples vanish in the Born-Infeld case. Finally, I will discuss how perturbation equations correspond to a supersymmetric quantum mechanical system.

Relatinng Neutrino Masses and Mixing with Dark Matter and the Baryon Asymmetry of the Universe
2023-04-21 10:30 - 12:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)

Nonlinear spectral broadening and pulse compression in multipass cells
2023-04-27 10:00 - 12:00 | Online
Resumo:Atualmente, tanto a comunidade de investigação como os utilizadores exigem fontes de laser capazes de fornecer impulsos de poucos ciclos com altas taxas de repetição, gerados de forma eficiente, utilizando tecnologia compacta, robusta e confiável. O uso de técnicas de pós-compressão, em particular alargamento espectral e compressão, abriu as portas para a geração de impulsos de poucos ciclos de forma eficiente e simples. Essa tecnologia éa base de uma nova geração de fontes de laser que são capazes de combinar tanto altas potências médias e instantâneas, e que melhoram as características dos impulsos, como contraste temporal, qualidade do perfile espacial e limpeza da polarização. Nesta dissertação, investigamos a técnica de alargamento espectral de multipassagem como um método de pós-compressão, mostrando que ela pode ser eficazmente usada em diversas montagens com energias que variam entre alguns nanojoule atéao joule. Em particular, um novo esquema óptico édemonstrado, capaz de contornar algumas das limitações das montagens anteriores e estender os limites para impulsos de energia mais altas. Também relatamos a primeira demonstração na faixa de energias sub-μJ como uma alternativa aos sistemas de compressão baseados em fibras.Além disso, a técnica de multipassagens é demonstrada com sucesso na gama de comprimentos de onda visível (515 nm), fornecendo, de forma eficiente, impulsos de femtosegundos a partir de uma fonte infravermelha. Por fim, édesenvolvido um protótipo de sistema de alargamento espectral e édemonstrada sua aplicação para uma fonte comercial com impulsos de um milijoule de energia. O seu desempenho e as suas características são estudadas e analisadas em termos de estabilidade e qualidade do feixe. Um fator de compressão do impulso acima de 10 éobtido transformando uma fonte de picosegundos diretamente numa fonte de femtosegundos com mais de 90% de eficiência, capaz de ser usada diretamente para uma variedade de aplicações.

Towards end-to-end speech-to-text summarisation
2023-04-27 10:00 - 11:00 | Online
ResumoA sumarização de fala para texto é uma técnica proeminente que permite economizar o tempo dispendido para acompanhar as notícias transmitidas diariamente. O surgimento de grandes modelos de linguagem a partir de aprendizagem profunda, que têm capacidades de geração de texto impressionantes, colocou o foco da investigação em sistemas de sumarização que produzem versões compactas e parafraseadas dos conteúdos de documentos, conhecidos como resumos abstrativos. A modelagem de ponta-a-ponta para sumarização abstrativa de fala para texto é uma abordagem promissora que oferece a possibilidade de gerar representações latentes ricas que aproveitam as informações não-verbais e acústicas do áudio, em oposição ao simples uso de informações linguísticas presentes nas transcrições geradas automaticamente em sistemas em cascata. No entanto, a pouca literatura sobre modelação ponta-a-ponta desta tarefa falha em explorar diferentes domínios, nomeadamente notícias. Modelamos a sumarização de fala para texto com sistemas em cascata e de ponta-a-ponta usando uma base de dados de notícias transmitidas em francês. Ao contrário da literatura disponível, a nossa nova implementação de ponta-a-ponta faz uso de dados externos, recorrendo à transferência de aprendizagem de um sumarizador de texto para texto pré-treinado. Experiências mostram que os resumos abstratos gerados pelos sistemas em cascata e de ponta-a-ponta são mais fortes do que uma linha de base extrativa. No entanto, o desempenho da implementação de ponta-a-ponta é pior do que a implementação em cascata, o que é objeto de uma extensa análise que inclui direções futuras para fechar esta lacuna.

A topological path to the Hawking temperature: astrophysical black holes and analogues
2023-04-27 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In this talk, a topological approach to determining the Hawking temperature of black holes is presented, embodied in a powerful, covariant formula involving the Euler characteristic of a (Euclideanized) spacetime manifold. This method has the advantage of allowing thermodynamical calculations to be simply carried out on spacetimes of complicated metrical form, as well as shining a light on the little-known but deep links between lower-dimensional topology and black hole thermodynamics. The method's efficacy for quantum soliton thermodynamics is also illustrated. Based on Phys. Rev. D 99, 044042 (2019) and New J. Phys. 21, 053042 (2019).

Electron microscopy studies of semi-conducting materials
2023-05-03 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Boron (B) has the potential for generating an intermediate band in cubic silicon carbide(3C-SiC), turning this material into a highly efficient absorber for single-junction solarcells. The formation of a delocalized band demands high concentration of the foreignelement, but the precipitation behavior of B in the 3C polymorph of SiC is not wellknown. Here, probe-corrected scanning transmission electron microscopy (STEM) andsecondary-ion mass spectrometry are used to investigate precipitation mechanisms inB-implanted 3C- SiC as a function of temperature. Point-defect clustering was detectedafter annealing at 1273 K while stacking faults, B-rich precipitates and dislocationnetworks developed in the 1573 - 1773 K range. The precipitates adopt therhombohedral B13C2 structure and trap B up to 1773 K. Above this temperature,higher solubility reduces precipitation and free B diffuses out of the implantation layer.Dopant concentrations of 1019 at.cm−3 were achieved at 1873 K. The concept of maximizing configurational entropy to enhance solid-state miscibilityinspires the exploration of unfamiliar composition spaces, and the popular, althoughimprecise, high-entropy (HE) designation seems destined to endure. The spotlight hasbeen on the mechanical properties of HE alloys, but interest in functional behavior isswiftly rising. In particular, the vast potential of combining metal solid solutions withstructural main group elements to form HE semiconductor compounds is becomingevident. The structure of a (Zn,Mn)(Fe,Co,Ni)Sb compound is investigated by powderX-ray diffraction, STEM coupled to atomically resolved energy dispersive spectroscopy(EDS) and by energy-filtered convergent-beam electron diffraction (CBED). Distinctionbetween the 216 (half-Heusler) and 225 (full-Heusler) space groups is hindered by thesimilar scattering power of the transition metals in XRD. However, the structure couldbe deciphered by STEM/EDS with the space group further attested by CBED.

Challenges to the Standard Cosmological Model
2023-05-03 16:00 - 17:00 | Centro de Congressos
Speaker: Dr Eleonora Di ValentinoTitle: Challenges to the Standard Cosmological ModelAbstract: The Lambda Cold Dark Matter (LCDM) model has been widely accepted as the standard cosmological model due to its good agreement with a broad range of cosmological data. However, recent studies have shown discrepancies among the model's key cosmological parameters, which have different levels of statistical significance. While some of these inconsistencies could be due to systematic errors, the persistence of such tensions across various probes suggests a potential failure of the canonical LCDM model. In this seminar, I will review the current tensions, including the Hubble constant disagreement, the S8 tension, and the CMB tension, and explore proposed solutions that could potentially alleviate them. However, I will also discuss the limitations of these proposed solutions and note that none of them have successfully resolved the discrepancies. Nevertheless, there are a few intriguing possibilities that warrant further investigation.

The Cosmic Ray Extremely Distributed Observatory (CREDO)
2023-05-03 17:00 - 19:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The Cosmic Ray Extremely Distributed Observatory (CREDO) is a recently formed,global collaboration dedicated to observing and studying cosmic ray ensembles (CRE):groups of minimum two cosmic rays with common primary interaction vertex or thesame mother particle. The CREDO program embraces testing the known CRE scenarios,and getting ready to observe the unexpected physics, it is also suitable for multimessenger and multi-mission applications. CRE could be formed both within classicalmodels (e.g. as products of photon-photon interactions), and exotic scenarios (e.g. asresults of decay of Super Heavy Dark Matter particles and subsequent interactions, Lorentz invariance violation), their fronts might be significantly extended in space andtime, and they might include cosmic rays of energies spanning the whole cosmic rayenergy spectrum. CRE are expected to be partially observable on Earth even if theinitiating interaction or process occurs as far as ~1 Gpc away, with a footprintcomposed of at least two extensive air showers with parallel arrival directions andcorrelated arrival times. Since CRE are mostly expected to be spread over large areas over hundreds ofkilometers or more, and because of the expected wide energy range of thecontributing particles, CRE detection might only be feasible when using the availablecosmic ray infrastructure collectively, i.e. as a globally extended network of detectors.CREDO is perfectly suited for probing the variation of fundamental constants in theaforementioned physical processes as well as for other applications like the search forsignatures of Earthquake precursors within the flux of cosmic rays.

Simulating Binary Neutron Star Mergers: Implications for Multimessenger Astronomy and Dark Matter Searches
2023-05-04 14:30 - 16:00 | Centro de Congressos ( -2 Floor of Civil Building)
ABSTRACT: Throughout the Universe, many high-energy, cataclysmic astrophysical collisions of neutron stars are continuously occurring. These collisions provide an excellent testbed to probe the properties of supranuclear-dense matter, to study the production of heavy elements, to allow for an independent measurement of the expansion rate of our Universe, and to perform an indirect search for dark matter. Essential for such studies are reliable models describing the merger dynamics. Keeping this in mind, numerical-relativity simulations can be seen as a prerequisite for a reliable interpretation of multi-messenger events, and to further develop gravitational-wave and electromagnetic transient models. We show some of our most recent results and identify how simulation can be used for multi-messenger studies and how simulations including dark matter admixed stars will open the door to identify the presence of dark matter in binary neutron star mergers.

Let's talk about... Fluidics!
2023-05-04 17:00 - 19:00 | Sala de Seminários do DF (2º piso)
Esta semana o tema de conversa do Physics@Coffee é Fluidics!

Black hole inner horizon instability in classical and semiclassical gravity
2023-05-11 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In this talk I will present an overview of the instabilities related to the presence of an inner horizon, focusing in particular on the effect these can have on the evolution of the geometry as a whole. I will begin by presenting a simple exact model of a black hole undergoing the classical mass inflation process, conveying an intuitive understanding of the origin of this instability, and describing in detail the resulting evolution of the geometry. Then I will discuss semiclassical backreaction. First, in parallel to the Hawking evaporation of the outer horizon, I will analyse the semiclassical evolution of a classically unperturbed inner horizon. Then, I will conclude by analysing semiclassical backreaction on a classically perturbed inner horizon (undergoing mass inflation), and discuss the possible outcomes of the evolution of a generic black hole in the full semiclassical theory.

Let's talk about... Black Holes!
2023-05-11 17:00 - 19:00

On the non-linear stability of the Cosmological region of the Schwarzschild-de Sitter spacetime
2023-05-16 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In this talk, I will discuss a strategy to prove the non-linear stability of the subextremal Schwarzschild-de Sitter spacetime in the stationary region near the conformal boundary. This technique is based on the extended conformal Einstein field equations and a conformal Gaussian gauge. The key observation is that the Cosmological stationary region of this exact solution can be covered by a non-intersecting congruence of conformal geodesics. Thus, the future domain of dependence of suitable spacelike hypersurfaces in the Cosmological region of the spacetime can be expressed in terms of a conformal Gaussian gauge. A perturbative argument then allows proving existence and stability results close to the conformal boundary and away from the asymptotic points where the Cosmological horizon intersects the conformal boundary. In particular, we show that small enough perturbations of initial data for the sub-extremal Schwarzschild-de Sitter spacetime give rise to a solution to the Einstein field equations which is regular at the conformal boundary.

Optical linear polarimetry in astrophysics
2023-05-18 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Polarimetry of the light provides unique insights into multiple astrophysical processes in the Universe that cannot be inferred from usual intensity observations. In this talk we review the importance of optical polarimetry in three different astrophysical systems: i) active galactic nuclei: supermassive black holes surrounded by accretion disks at the center of major galaxies, ii) kilonovae: the optical emission of compact neutron star mergers that are preceded by gravitational wave emission, and iii) supernovae: the explosive end of massive stars or of white dwarfs in binary systems. We discuss how different theoretical models of the progenitor and physical processes of these systems shape the predicted optical linear polarimetry and compare them to current observations. We pay particular attention to the systematic bias of interstellar polarization from dust in the line of sight.

Probing the Quark Gluon Plasma with B0s and B+ Mesons: Cross Sections in pp and Nuclear Modification Factors in PbPb Collisions
2023-05-18 16:00 - 18:00 | Sala C10 Pavilhão Central, Piso 1/ Online (Contactar Ana Bela Cardoso para password) ana.bela.cardoso@tecnico.ulisboa.pt
O plasma de quark e gluões (QGP) é uma das mais intrigantes fronteiras da Física de Partículas. Esta forma exótica da matéria forma-se apenas em condições extremas, de temperatura e densidade, e que agora são recreáveis através de colisões relativístas de iões pesados. O estudo deste fenómeno fornece informações essenciais sobre a sua extensa formulação teórica, a cromodinâmica quântica. Os mesões B têm-se recentemente mostrado extremamente relevantes para sondar o QGP, particularmente devido ao longo tempo de vida dos quarks b permitirem tanto registar os efeitos do meio que atravessaram como uma reconstrução mais clara. Explorando esta última vantagem, ao longo desta tese são realizadas medições das secções eficazes dos mesões B^+ e B_s^0 em função do momento transversal, p_T, em colisões protão-protão a \sqrt s=5.02\ TeV. Os dados analisados foram adquiridos pelo detetor CMS, durante a operação do LHC em 2017. O sinal dos dois mesões B foram respetivamente explorados nos canais de B_s^0\rightarrow J/\psi\left(\mu^+\mu^-\right)\phi\left(K^+K^-\right)\ e B^+\rightarrow J/\psi(\mu^+\mu^-)K^+. As secções eficazes medidas foram comparadas à previsão teórica FONLL e observou-se uma boa concordância. Para quantificar os efeitos do QGP no espetro de mesões B determina-se os respetivos fatores de modificação nuclear, R_{AA}. Em ambos os mesões observa-se uma elevada supressão da sua produção, sendo os mesões B_s^0 ligeiramente menos suprimidos que os mesões B^+.\ \ A baixo p_T, o R_{AA} do mesão B_s^0 é compatível com a hipótese de coalescência entre quarks

Let's talk about... the Higgs boson!
2023-05-18 17:00 - 19:00

Quantum phases of quasiperiodic matter
2023-05-24 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Quasiperiodic systems offer a myriad of fascinating phenomena, from localization transitions in one or higher dimensions, to intriguing topological properties. There has been a continued interest in these systems due to their experimental accessibility across diverse platforms, including ultracold atoms and trapped ions, photonic and phononic media and, more recently, moiré materials. In this seminar, we will delve into our recent research on the quantum phases of both non-interacting and interacting quasiperiodic systems. We will start by introducing a theoretical framework that we have developed to characterize the localization phase diagrams of non-interacting 1D quasiperiodic systems, that includes extended, localized, and even critical multifractal phases. This theory, based on a renormalization-group procedure, allowed us to connect widely different models in the literature and in some cases, fully analytically characterize the phase diagrams. We will then generalize our theory to interacting quasiperiodic systems. By applying this generalization to a broad class of 1D quasiperiodic chains, we will unveil a compelling finding: short-range interactions become irrelevant in the vicinity of ground-state localization-delocalization transitions. Finally, we will explore the role of quasiperiodicity in moiré systems. Through illustrative examples, we will demonstrate that quasiperiodicity can be of crucial importance, being responsible for creating non-trivial states of matter, inaccessible in the periodic case.

Nucleosynthesis and electromagnetic transients from neutronstar mergers and rare types of core-collapse supernovae
2023-05-25 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Gravitational-wave and multi-messenger astronomy shed light on the astrophysics of black-holes and neutron-stars and also allow for unique probes of fundamental physics. I will discuss recent results on how the mergers of neutron stars as well as other explosive systems such as the death of massive, rotating stars give rise to the formation of heavy elements in the universe. In particular, I will discuss recent results at the interface of numerical relativity, relativistic astrophysics, neutrino physics, and nuclear astrophysics, and highlight how multi-messenger astronomy may lead to the answer of a 70-year old fundamental question in physics: How does the Universe create the heaviest elements?

Let's talk about... Burning fusion plasmas
2023-05-25 17:00 - 19:00

Towards Quantum Simulation of Bound States Scattering
2023-05-30 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The last years have seen a rapid development of applications of quantum computationto quantum field theory. The first quantum algorithms for simulation of scattering havebeen proposed in the context of scalar and fermionic theories, requiring thousands oflogical qubits. These algorithms are not suitable to simulate scattering of incomingbound states, as the initial state preparation relies typically on adiabaticallytransforming wavepackets of the free theory into wavepackets of the interactingtheory.In this talk, I will present a strategy to excite wavepackets of the interactingtheory directly from the vacuum of the interacting theory, allowing for preparation ofstates of composite particles that can be taken as initial states of a scatteringsimulation. This is the first step towards digital quantum simulation of scattering ofbound states. The approach is based on the Haag-Ruelle scattering theory, whichprovides a way to construct creation and annihilation operators of a quantum fieldtheory in a full, nonperturbative framework. To show that the idea works for quantumcomputation, I will describe a quantum algorithm implementing the approach.

Probing the system’s dynamics around dynamical quantum phase transitions
2023-05-31 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Dynamical quantum phase transitions (DQPTs) are defined by the non-analyticity intime in the Loschmidt echo, which measures the overlap between the time-evolvedstate and the initial state when a system is brought out of equilibrium. While the studyof DQPTs has been thriving, how the system behaves around the critical time remainsan open question. In this talk, we will explore the dynamics of the many-body systemsaround DQPT using various probes. We find that the extrema in the time evolutionof the equilibrium order parameter are connected to DQPTs in the Su-SchreifferHeeger model. We will also discuss how the correlations spread under the influence ofinter and intra- cell interactions in the model as probed by unequal time Greenfunctions. The concept of Loschmidt amplitude spectrum – an extension of theLoschmidt echo measures will also be introduced. The spectrum suggests there is apopulation redistribution in the momentum space across the transition in thequantum Ising model, providing us new insight into the behaviour of the systemaround DQPTs.

Spin Textures and Spin Waves
2023-05-31 16:00 - 17:00 | PA1, Mathematics
Title: Spin Textures and Spin WavesSpeaker: Prof. Daniela Petti (Politecnico di Milano)Abstract:Spin textures are nonuniform configurations in the arrangement of spins in magnetic materials, which are raising interest as active components in data storage and signal processing. During this lecture, different spin textures, such as domain walls, vortices and skyrmions, will be introduced and their main applications will be discussed. We will also examine different lithographic approaches to stabilize spin textures; indeed spin textures are stable, have a high degree of tunability and have nanoscale dimensions. In the second part of the lecture, spin waves will be introduced. They are propagating perturbation in the spin lattice of ordered magnetic materials. In analogy to photonics, magnonics uses spin waves to carry and process information at the GHz-THz frequency, but differently, the typical wavelength of spin waves at these frequencies is in the nanometer range, while the wavelength of electromagnetic radiation is order of magnitude longer. Currents of magnons, the equivalent quanta of spin waves, can carry energy (frequency) and angular momentum (spin) without motion of charges, which makes them promising for beyond CMOS computing, due to the absence of Joule heating. We will finally explore the interaction of the spin textures with the spin waves, focusing on how spin textures can be used to manipulate spin waves at the nanoscale. Some example will be discussed.

Numerical relativity and semi-analytical waveforms for the fourth observing run of the LIGO-Virgo-KAGRA detectors
2023-06-01 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: The successful observation campaigns by the global gravitational wave detectors network and the expectation of hundreds of new systems detected in the upcoming observation run, O4, starting on May 2023, are paving the way for the detection of GW events with challenging physical properties. Particularly, the large number of expected detections of binary black holes in O4 may lead to clear detection of orbital eccentricity and spin-precession, which would provide key information about the formation channels of such binaries. However, so far the waveform models used by the community, including the LIGO, Virgo and Kagra collaborations, to detect and estimate the parameters of the gravitational wave signals assume quasi-circular orbits or non spin-precessing binaries. In this presentation, I will describe the current status of ready-to-use quasi-circular waveform models for O4, as well as current efforts to model the gravitational signal from generic binary black holes, including the production of accurate eccentric numerical relativity simulations and some of their applications, such as comparisons with small mass ratio perturbation theory results to bridge the gap between comparable masses and extreme mass ratio systems in elliptical orbits.

Let's talk about... Quantum Matter!
2023-06-01 17:00 - 19:00

Constraining constant and tomographic coupled dark energy with low and high redshift probes
2023-06-06 14:30 - 16:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
ABSTRACT: We consider coupled dark energy (CDE) cosmologies, where dark matter particles feel a force stronger than gravity, due to the fifth force mediated by a scalar field which plays the role of dark energy. We perform for the first time a tomographic analysis of coupled dark energy, where the coupling strength is parametrized and constrained in different redshift bins. This allows us to verify which data can better constrain the strength of the coupling and how large the coupling can be at different epochs. First, we employ cosmic microwave background data from Planck, the Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT), showing the impact of different choices that can be done in combining these datasets. Then, we use a range of low redshift probes to test CDE cosmologies, both for a constant and for a tomographic coupling. In particular, we use for the first time data from weak lensing (the KiDS-1000 survey), galaxy clustering (BOSS survey), and their combination, including 3x2pt galaxy-galaxy lensing crosscorrelation data. We do not find evidence for nonzero coupling, either for a constant or tomographic case. A nonzero coupling is however still in agreement with current data. For CMB and background datasets, a tomographic coupling allows for β values up to one order of magnitude larger than in previous works, in particular at z<1. The use of 3x2pt analysis then becomes important to constrain β at low redshifts, even when coupling is allowed to vary: for 3x2pt we find, at 0.5

Unraveling Integrability and Quantum Chaos in Open Quantum System
2023-06-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
We study the quantum and semiclassical dynamics of the dissipative SU(3) BoseHubbard trimer model. By setup non-cyclic and cyclic limits, we could study thegapped and gapless Liouvilian spectrum and the dynamics of steady states. Employingexact diagonalization on the quantum Liouvillian superoperator and steady-statedensity matrix, we characterize quantum chaos through the level statistics of theireigenvalues. The gapped case exhibits a unique well-defined steady state, while thegapless one possesses multiple steady states with regular, limit cycles and chaotictrajectories. The spacing level statistics of the density matrix associated with a unique steady stateor regular trajectories is a Poisson, while for chaotic multiples steady states thedistribution is Gaussian Unitary Ensemble. From the semi-classical point of view, we obtained the equations of motion by astandard Keldysh path integral method together with the proper stochastic Langevinequation. We show robust evidence pointing out a deep connection between thequantum-level statistics of the density matrix and the distribution of Lyapunovexponents associated with classical trajectories for long times.

Exploring and the Low Surface Brightness Universe with Deep Imaging
2023-06-07 16:00 - 17:00 | PA1, Mathematics
Title: Exploring and the Low Surface Brightness Universe with Deep ImagingSpeaker: Prof. Pierre-Alain DucAbstract:The exploration of the Low Surface Brightness (LSB) Universe currently motivates several surveys across the world, carried out with a number of instruments, and provides observational constrains for numerical simulations. It impacts multiple scientific fields, including the ISM structure, galaxy formation and evolution and cosmology, and has generated passionate debates, for instance regarding the very existence, nature and properties of the so called Ultra-Diffuse-Galaxies. Meanwhile the community prepares for the exploitation of next generation surveys, including Euclid and LSST. I will review the current efforts done by our group in this active field of science and will in particular focus on what deep imaging can tell us about the way galaxies have assembled their mass through mergers.

Effects of Disorder in Higher-order Topological Insulators
2023-06-09 13:30 - 15:00 | Anfiteatro VA1, Pavilhão de Civil/ Online
Resumo:Isolantes topológicos são materiais com propriedades topológicas exóticas protegidas por simetrias, que foram recentemente generalizados para ordem superior. Tendo em conta que desordem ocorre em qualquer implementação prática, é importante compreender como afecta estes sistemas. Neste trabalho, aplicamos desordem que preserva a simetria quiral aos modelos prototípicos de Bernalcazar-Bernevig-Hughes (BBH) para isolantes topológicos de ordem superior. Revemos os invariantes topológicos dos sistemas limpos, com o método dos nested Wilson loops no espaço recíproco. Estudamos um sistema 2D desordenado, encontrando-se um isolante topológico de Anderson de segunda ordem (SOTAI) induzido por desordem, com momento quadropular quantizado, em fases com e sem gap. Com o aumento de desordem, o sistema transita para um regime de Griffiths de comportamento multifractal, seguido de um isolante de Anderson trivial. Os resultados centrais são a 3D, onde encontramos o primeiro exemplo de um isolante topológico de Anderson de terceira ordem (TOTAI), com momento octupolar quantizado. Para desordem mais intensa, o TOTAI transita para um metal difusivo trivial, tornando-se um isolante de Anderson a desordem ainda superior. Os resultados são apoiados por uma análise numérica exata e detalhada, revelando também estados protegidos localizados nos cantos, tanto em 2D como em 3D. Em 3D, a transição induzida por desordem para a fase TOTAI também se capta analiticamente com precisão notável utilizando a aproximação auto-consistente de Born. Os nossos resultados demonstram que desordem pode induzir fases topológicas de terceira ordem em 3D, aumentando assim a classe de isolantes de Anderson topológicos de ordem superior conhecidos.

Spin-orbit entanglement in two-dimensional layered materials
2023-06-14 16:00 - 17:00 | PA1, Mathematics
Abstract: Spin-orbit coupling (SOC)—a relativistic interaction which entangles a particle’s motion with its quantum mechanical spin—is fundamental to a wide range of physical phenomena, spanning from the formation of topological insulators to the spin Hall effect of light. Recent years have seen remarkable progress in the probing, enhancing and tailoring of SOC in artificial materials, specifically heterostructures, made of two or more individual flakes of graphene-like crystals arranged in a stack. From the electrical control of spin-valley coupling in bilayer graphene [1], to the reversible spin-charge conversion in graphene with proximity-induced SOC courtesy of atomically-thin semiconductors [2], these discoveries challenge our previous notions on the possible behaviour of spin-orbit coupled electrons at hetero-interfaces.In this talk, I will show that the rich array of spin-dependent phenomena facilitated by proximity-induced SOC in graphene can be understood from the perspective of quantum information theory, i.e., as arising from quantum-mechanical entanglement between real spin and lattice-pseudospin degrees of freedom [3]. The proximity-induced SOCand ensuing spin-spin entanglement are sensitive to the atomic registry between graphene and its high-SOC partner material, which opens up interesting possibilities for spin-charge interconversion, including a current-induced spin polarization tuneable by means of a simple interlayer rotation angle [4].References:[1] “Anisotropic spin currents in graphene”, https://physics.aps.org/articles/v11/s108[2] “Proposal for unambiguous electrical detection of spin-charge conversion in lateral spin valves”, S. Cavill, C. Huang, M. Offidani, Y.-H. Lin, M. Cazalilla and A. Ferreira, Phys. Rev. Lett. 124 (2020).[3] “Theory of spin-charge-coupled transport in proximitized graphene: an SO(5) algebraic approach”, A. Ferreira, J. Phys. Mater. 4, 045006 (2021).[4] “Twist angle controlled collinear Edelstein effect in van der Waals heterostructures”, A. Veneri, D. Perkins, C. Péterfalvi and A. Ferreira, Phys. Rev. B 106, L081405 (2022).

Vector-like quarks of Nelson-Barr type: an overview
2023-06-15 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The Nelson-Barr mechanism to solve the strong CP problem requires vector-like quarks (VLQs) to transmit the spontaneous CP breaking to the SM. Even in the scenario where the spontaneous CP breaking sector is inaccessible, these VLQs can be at the TeV scale in reach at present colliders. In this talk I will show how these VLQs of Nelson-Barr type differ from generic VLQs and find from parameter counting that one less parameter is needed. In particular, for one VLQ of Nelson-Barr type, there is only one CP odd quantity that is responsible for all CP violation in the quark sector. In this case, I will show that the model is largely flavor safe. A global fit on the relevant flavor observables is also performed, and a comparison is made to the case of one generic VLQ. We find that the allowed parameter space for the VLQ Yukawa couplings and the mixing to the SM are confined to a region much smaller than in the generic case, making the NB case falsifiable in principle. I conclude presenting some recent analyses for the case in which two VLQs (either of down or up-type) are considered at the same time.

GR-Athena++: Puncture evolutions on vertexcentered oct-tree AMR and compact finite differencing
2023-06-15 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: GR-Athena++ is a general-relativistic, high-order, vertex-centered solver that extends the oct-tree, adaptive mesh refinement capabilities of Athena++. Dynamical spacetimes are simulated using the Z4c formulation of numerical relativity coupled to the moving puncture gauge. Robust and accurate binary black hole (BBH) mergers are demonstrated. GR-Athena++ leverages the task-based parallelism paradigm of Athena++ to achieve excellent scalability. Strong scaling efficiencies above 95% for up to 1.2×1e4 CPUs and excellent weak scaling up to 1e5 CPUs are measured for production BBH runs. GR-Athena++ provides infrastructure for the robust simulation of compact binary coalescences and offers a viable path towards numerical relativity at exascale. In this talk, a general overview of features outlined above will be provided. Recent developments will also be discussed together with our incorporation of compact finite differencing for vacuumsector evolution.

Let's talk about... The Cosmos!
2023-06-15 17:00 - 19:00

Causality constraints on K-essence: Superfluid dark matter to modified gravity
2023-06-20 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Superfluid dark matter is a novel way of reconciling the apparent discrepancy between galactic phenomenology and LCDM cosmology. The advantage of these models is that on cosmological scales they can play the role of CDM, while on galactic scales there is a phase transition to a superfluid, and the nontrivial dynamics in this regime can reproduce the observed Tully-Fisher relation. However, we find in general these models exhibit a breakdown of causality, which indicates they would resist having any standard UV completion. Constructing a class of causal k-essence theories, instead of dark matter we can consider these as scalar modifications of gravity. In these theories the strength of the new force grows with increasing density, becoming most relevant in the densest astrophysical environments. We consider various observational constraints on this class of modified gravity theories, with the strongest constraint coming from equilibrium of neutron stars.

Thermodynamics of black holes and self-gravitating hot matter
2023-06-21 14:00 - 16:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract: Black holes and self-gravitating hot matter can be viewed as thermodynamic objects. This fact reveals the existence of a link between thermodynamics and gravitation, since at a fundamental level thermodynamics stems from the quantum behavior of the systems. The essence of the connection is still unknown, but it is indicated that comes from the quantum character of gravitation. To shed light on the nature of this link, it is essential to analyze the thermodynamic properties of curved spacetime with black holes and self-gravitating matter together. It is also interesting to generalize the analysis to higher dimensions, in connection with theories of quantum gravity that require dimensions higher than four. In this seminar, I will mainly focus on two works: I will present the thermodynamic properties of a charged spherical hot thin shell in higher dimensions, by imposing the first law of thermodynamics, showing its entropy and its thermodynamic stability, where suggestive equations of state have been chosen for the shell, clarifying thus the contributions of the self-gravitating nature of ordinary matter to the entropy and other thermodynamic quantities; I will also present the grand canonical ensemble of a d-dimensional charged black hole in a cavity, through the Euclidean path integral approach in the zero loop approximation, which has two solutions for the horizon radius of the black hole, where the solution with the largest radius is stable. In addition, I will present the ongoing work on the canonical ensemble of charged black holes in acavity, the canonical ensemble for pure self-gravitating hot matter shells, and the grand canonical ensemble of black holes and matter shells, as well as other recent projects.

Integration algorithms for charged-particle dynamics in magnetised plasmas
2023-06-22 09:00 - 11:00 | Online
Resumo:Neste projeto de tese, a validade do modelo centro-guia (CG) foi testada a partir da comparação entre as trajetórias de órbita completa (OC) e de CG de alfas de fusão em configurações magnéticas complexas típicas de dispositivos de fusão.Para realizar as integrações OC, a funcionalidade da biblioteca \textsc{gyronimo} foi estendida com o sistema dinâmico da força de Lorentz em coordenadas curvilíneas e outros algoritmos. Três integradores FO foram comparados: Boris Clássico, Boris Curvilíneo e Runge-Kutta de 4ª ordem. Com base nas propriedades de conservação das constantes de movimento dos algoritmos e no formato da trajetória em campos eletromagnéticos simples em coordenadas toroidais, o método numérico mais preciso para integrações longas foi escolhido para as subsequentes integrações OC.Em seguida, diversos casos de órbitas de alfas obtidas por integrações OC e CG no equilíbrio magnético estático de um tokamak axissimétrico e de um stellarator não-axissimétrico foram comparados. Demonstra-se que, apesar de os resultados OC e CG concordarem para o equilíbrio tokamak, há casos em que as abordagens discordam nos campos magnéticos 3D mais complexos de um dispositivo stellarator.Para determinar a relevância das discrepâncias nas órbitas OC e CG no equilíbrio stellarator escolhido, foi implementada e executada uma simulação do confinamento de partículas alfas de fusão, onde se verificou que a abordagem OC previa mais do dobro de alfas perdidos que a abordagem CG. Além disso, verificou-se que as alfas são perdidas na mesma região para ambos tipos de integração, mas distribuídas de forma diferente no interior da mesma.

Scalar field solutions in the Weyl class
2023-06-22 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: After briefly reviewing the properties of the Weyl-scalar field system we derive and analyze a particularly simple phantom scalar field solution within the Weyl geometry (a natural counterpart of the Curzon--Chazy spacetime). We show that this solution contains a wormhole throat which connects to a region that is not asymptotically flat and that behaves like a one-directional time machine. We investigate its conformal structure and analyze a non-scalar singularity appearing beyond the wormhole throat. Various definitions of mass of the spacetime are compared in the presence of phantom matter.

Tidal deformability of gravitational atoms
2023-06-23 14:00 - 16:00 | Sala P12 Pavilhão de Matemática, Piso 2
Resumo: Na última década, a deteção de ondas gravitacionais (OG) provou ser uma ferramenta útil para estudar objetos astrofísicos, nomeadamente sistemas com um campo gravítico forte como os buracos negros (BNs). Espera-se que esta revele utilidade experimental para os modelos de extensão do Modelo Padrão como a natureza de partículas ultraleves e Matéria Escura. Se existirem campos bosonicos ultraleves em torno de BNs, o processo de superradiância, que é um mecanismo de amplificação de ondas, pode levar a uma instabilidade que causa o seu crescimento exponencial em amplitude e extrai massa e momento angular do BN até que se forme um condensado (ou nuvem) que roda com o BN. Esta nuvem depois emite sinais de OGs que podem ser analisados e transmitir conhecimento em relação a nova física. Nesta tese focamo-nos na deformabilidade de maré destes BNs "vestidos" com um campo escalar através do cálculo de alguns dos seus números de Love de maré (NLM). Estes coeficientes quantificam a resposta induzida na estrutura multipolar de um objeto devido à sua interação gravítica com outro corpo maciço. Fazemos isto nas aproximações de limite Newtoniano, onde se assume que o campo gravítico é fraco e os objetos têm velocidades baixas, e de pequeno-acoplamento (entre o campo escalar e o BN). Visto que foi provado que os BNs têm NLM nulos, qualquer deteção de OGs cuja assinatura implique NLM não-nulos pode indicar a existência de partículas ultraleves.

The Teukolsky equation on Kerr black hole spacetimes
2023-06-26 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:he Teukolsky master equations describe the gauge invariant degrees of freedom in linear gravitational perturbations of the Kerr black hole family.In this talk, we focus on separable solutions to the Teukolsky equations, for which superradiance and trapping phenomena can be understood. Particular emphasis will be given to mode stability, that is non-existence of exponentially growing or bounded but non-decaying separable solutions. A corollary of our analysis is that general solutions to the Teukolsky equations are bounded and decay in time; this is a key first step in establishing (linear) stability of Kerr black holes.This talk contains joint work with Marc Casals (Leipzig/CBPF/UC Dublin) and Yakov Shlapentokh-Rothman (Toronto).

The remarkable role of the vector-like quark doublet in the Cabibbo angle and W-mass anomalies
2023-06-27 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The combination of precise determinations of $V_{us}$ and $V_{ud}$ hints towards a violation of the CKM first row unitarity at about $3\sigma$ level. A possible explanation can be the mixing of SM quarks with vector-like quarks, up or down type $SU(2)_L$ singlets or $SU(2)_L$ doublet, with mass of few TeV, having large enough mixings with the lighter quarks. A different solution may come from the introduction of the gauge horizontal family symmetry acting between the lepton families and spontaneously broken at the scale of about 6 TeV. Another tension in the value of the Cabibbo angle is also reported at $3\sigma$ level, between two determinations of $V_{us}$ obtained from semi-leptonic and leptonic kaon decays. A vector-like doublet can account for this discrepancy. Although one extra multiplet cannot entirely explain all the Cabibbo anomalies, a combination such as two species of isodoublets, or one isodoublet and up or/and down type isosinglet can be a complete solution.Moreover, the recent measurement of the $W$-boson mass by the CDF Collaboration exhibits significant tension with the SM prediction, intensifying the conflict that may arise in models addressing the CKM unitarity violation. One vector-like doublet of quarks mixing with light quarks and the top quark can be the common origin of the CKM unitarity deficit or the tension in $V_{us}$ determinations and the positive shift in $W$-boson mass, without conflicting with flavour-changing phenomena and electroweak observables.

Applications to biological networks of adaptive Hagen-Poiseuille flow on graphs
2023-06-29 11:00 - 13:00 | Online
Physarum polycephalum é um protista unicelular com numerosos núcleos cujo corpo é constituído por uma rede de veias. À medida que explora o seu meio, adapta-se e otimiza a sua rede, tendo em conta estímulos externos. Foi demonstrado que exibe comportamentos complexos, como resolver labirintos, encontrar o caminho mais curto e criar redes robustas, eficientes e económicas. Vários modelos foram desenvolvidos para tentar simular a adaptação da sua rede para compreender os mecanismos por detrás do seu comportamento e desenvolver redes eficientes. Esta tese pretende estudar um modelo recentemente desenvolvido e fisicamente consistente baseado em fluxos de Hagen-Poiseuille adaptativos; para tal, irá determinar propriedades das árvores produzidas pelo modelo e irá examiná-las para determinar se são realistas e consistentes com a experiência. Esta tese também pretende usar o mesmo modelo para produzir redes curtas e eficientes, aplicando-o a uma rede de transporte real. Observámos que o modelo é capaz de criar redes que são consistentes com outras redes biológicas: seguem a lei de Murray no estado estacionário, mostram estruturas semelhantes às presentes nas redes do Physarum e ainda exibem peristalse (oscilação dos raios das veias) e shuttle streaming (o movimento de trás para a frente do citoplasma do Physarum) em algumas partes das redes.Usámos também o modelo em conjunto com diferentes algoritmos estocásticos para produzir redes curtas e eficientes; quando comparadas com a rede ferroviária de Portugal continental, todos os algoritmos produziram redes mais eficientes que a rede real e alguns produziram redes com melhor relação custo-benefício.

Magnetic sensors for low field detection: thin films and architectures
2023-06-29 14:00 - 16:00 | Online

- The Teukolsky equation on Kerr black hole spacetimes
2023-06-29 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT:The Teukolsky master equations describe the gauge invariant degrees of freedom in linear gravitational perturbations of the Kerr black hole family. In this talk, we focus on separable solutions to the Teukolsky equations, for which superradiance and trapping phenomena can be understood. Particular emphasis will be given to mode stability, that is non-existence of exponentially growing or bounded but non-decaying separable solutions. A corollary of our analysis is that general solutions to the Teukolsky equations are bounded and decay in time; this is a key first step in establishing (linear) stability of Kerr black holes. This talk contains joint work with Marc Casals (Leipzig/CBPF/UC Dublin) and Yakov Shlapentokh-Rothman (Toronto)

Deciphering jet quenching effects through a quantile ratio
2023-07-03 09:00 - 11:00 | Online
Jatos hadrónicos surgem da fragmentação de quarks ou gluões altamente energéticos produzidos em aceleradores de partículas. Em colisões de iões pesados, a interação de núcleos origina um estado de matéria nuclear conhecido como Plasma de Quarks e Glúons (QGP). Ao atravessar este meio, os jatos sofrem perdas energéticas devido às interações com o QGP, resultando na supressão e modificação dos jatos em relação às colisões de protão-protão. Ao estudar observáveis dos jatos, as propriedades e dinâmica do QGP são percebidas. Dentro deste contexto, esta análise avalia os observáveis por meio de simulações baseadas em JEWEL, um gerador de eventos Monte Carlo que inclui efeitos de supressão de jatos. Para aprimorar a compreensão dos mecanismos de perda de energia dos jatos, este estudo examina o papel das partículas dispersas no meio, juntamente com um análise em quantis para mitigar os efeitos de migração de bins e permitir uma quantificação direta da energia média perdida pelos jatos. Além disso, a dependência da perda de energia dos jatos com o comprimento do meio atravessado será explorada considerando vários aspectos geométricos da colisão, especificamente a influência da forma do meio e os efeitos de meios menos densos.

Higher Rank Gauge Theories - A Quantum Monte-Carlo Study
2023-07-03 15:00 - 17:00 | Online
Teorias de gauge representam algumas das forças fundamentais do Universo, mas também modelos efetivos de Matéria Condensada a baixa energia. Enquanto para acoplamento fraco as teorias de gauge admitem uma formulação continua, para acoplamento forte apenas estudos na rede são viáveis. Recentemente, mostrou-se que teorias de gauge de ordem superior têm excitações geometricamente restritas - fases fractónicas. Nós estudamos o diagrama de fases de uma delas- a Hollow Rank-2 U(1) com matéria bosónica - na rede, com previsões numéricas de Monte Carlo. Foram obtidas previsões analíticas para gauge pura (sem matéria), onde as excitações de carga são quadrupolares. Para acoplamento forte, obtivemos uma lei de volume concomitante com uma Fase de Confinamento Forte, onde o potencial quadrupolar cresce quadraticamente com a separação entre cargas. Para acoplamento fraco, encontramos a Fase de Confinamento Eletrostático com uma lei de área e potencial quadrupolar linear. Também estudamos a inclusão de campos de matéria Higgs bosónica com carga p=1. Os resultados indicam que as Fases de Confinamento Forte e Confinamento Eletrostático estendem-se para acoplamento fraco com matéria. Quando os campos de matéria e gauge estão fortemente acoplados, uma fase distinta surge. Denominada Fase Higgs, em analogia com U(1) de ordem-1. Para um acoplamento infinito com matéria, apenas a Fase de Confinamento Forte sobrevive. No acoplamento infinito de gauge, a teoria reduz-se ao modelo XY-plaquete (3+1)D. Apresentamos o primeiro diagrama de fases completo para um modelo fractónico com matéria bosónica, ampliando o conhecimento sobre esses candidatos a memória quântica tolerante a falhas.

Automated ECG classification using Deep Neural Networks to predict arrhythmia recurrence in patients with atrial fibrillation
2023-07-04 10:00 - 12:00 | Online
Nesta tese é feito um resumo teórico focado no coração e na sua eletrofisiologia, nomeadamente na onda P do eletrocardiograma de superfície, seguido de um estudo prospetivo acerca da possibilidade do uso de redes neuronais em R na previsão de recorrência em pacientes com fibrilhação auricular sujeitos a uma ou mais ablações. A previsão é baseada quer em parâmetros eletrocardiográficos, principalmente da onda P como validação de conceito, quer em valores clínicos como o sexo e a idade. Os canais II, V1 e aVF do ECG, canais onde a onda P é mais acentuada, foram usados na extração dos primeiros parâmetros, inseridos posteriormente na rede neuronal. O modelo desenvolvido utiliza pacientes com arritmia e tem o potencial de identificar recorrência, ainda que o número de casos utilizados para treino e teste da rede neuronal seja reduzido. Este método não é ainda utilizado na prática clínica.Com o aumento da base de dados utilizada nas fases de treino e teste, é possível aumentar a eficácia do modelo.

Digital Twin of the Electricity Generation and Demand in Portugal
2023-07-04 11:00 - 13:00 | Sala C10, Pavilhão Central, Piso 1
Há várias metas energéticas a cumprir nas próximas décadas. Grande parte delas não será atingida se não compreendermos melhor como gastamos energia. O propósito da minha tese é expandir essa compreensão no cenário português, criando um digital twin do consumo elétrico municipal, mais precisamente, um modelo horário que descreva o consumo de diferentes setores de atividade em todos os municípios de Portugal. Isto é obtido ao expandir consumo setorial anual usando perfis horários relativos a cada setor.Os resultados foram validados com recurso a dois conjuntos de dados distintos, um possuindo consumo horário nacional, e o outro consistindo em consumo mensal municipal. Uma simples aplicação do modelo foi testada, nomeadamente a previsão do consumo elétrico de 2022. Isto foi feito prevendo o consumo anual de 2022 por município e setor, e depois expandindo com recurso ao modelo, sendo a validação feita da mesma forma.No final, os resultados do modelo e da aplicação mostraram se positivos, com um erro inferior a 15% em 91% dos municípios do modelo, e em 89% dos municípios na aplicação, estando o modelo pronto para ser integrado em ferramentas de planeamento energético a nível municipal/nacional.

The diffusion of information in social media – How much complexity do we need?
2023-07-04 12:00 - 14:00 | Online
Com o advento da era das redes sociais, a quantidade de conteúdo disponível aumentou radicalmente. A informação tem de competir pelo nosso tempo e nós escolhemos o que preferimos - a difusão da informação é, portanto, ditada pela economia da atenção. Como resultado, enquanto que alguns pedaços de informação são amplamente partilhados, a maioria deles não é partilhado de todo. A causa desta distribuição é frequentemente atribuída ao fenómeno de Preferential Attachment (ligação preferencial), no qual cada novo vértice adicionado à rede tem uma probabilidade maior de estabelecer uma ligação com um vértice já bem ligado. O resultado final é uma distribuição do tipo Power Law: alguns vértices têm muitas ligações, mas a maioria deles tem um valor muito baixo. A distribuição observada dos tamanhos de cascata pode surgir desta estrutura subjacente da rede. No entanto, a popularidade de um determinado pedaço de informação também pode desempenhar um papel importante. Chamamos a esta característica, "fitness". Com o nosso trabalho, pretendemos determinar o que descreve melhor a difusão de informação: se o fitness, a rede ou uma combinação de ambos. Para o fazermos, vamos usar dados do Twitter, uma rede social. O Twitter permite estudar o problema de um modo quantitativo, essencial para o estudo da difusão de informação no mundo real.

Stochastic Dynamics of Human Institutions
2023-07-04 14:00 - 16:00 | Online
Compreender as condições que permitem a emergência, evolução e manutenção de cooperação é um problema teórico com importância actual. Por exemplo, a sua resolução poderia ajudar a resolver problemas de acção colectiva, ou seja, problemas onde as actuais instituições sucumbem à Tragédia dos Comuns. Os efeitos de Sanções e Recompensas já foram analisados como uma ferramenta efectiva para evitar a Tragédia dos Comuns e este trabalho pretende analisar uma nova tipologia institucional que combina recompensas e sanções juntamente com um mecanismo eleitoral, no âmbito da Teoria de Jogos Evolutiva. Em particular, propomos um modelo onde indivíduos que fazem parte de uma determinada população participem num jogo N-pessoas com quatro estratégias à sua disposição: cooperar, desertar, punir ou recompensar. Concluímos que esta tipologia é mais eficaz que as alternativas mais simples a promover cooperação

Stellar flare spectroscopy with ESPRESSO: detecting planets around flaring stars
2023-07-05 11:00 - 13:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física) - Online

Ga2O3 field effect transistors for sensor applications
2023-07-06 10:00 - 12:00 | Anfiteatro PA2 (Piso -1 do Pavilhão de Matemática)

Machine learning in cardiac electrophysiology: localization of accessory pathways in Wolff-Parkinson-White syndrome patients with 12-lead electrocardiographic analysis
2023-07-06 12:00 - 14:00 | Anfiteatro PA2(Piso -1 do Pavilhão de Matemática)

How Fast Does the Bubble Grow? Hydrodynamical Obstruction in Numerical Simulations
2023-07-06 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Terminal velocity reached by bubble walls in first order phase transitions is an important parameter determining both primordial gravitational-wave spectrum and production of baryon asymmetry in models of electroweak baryogenesis. We developed a numerical code to study the real-time evolution of expanding bubbles and investigate how their walls reach stationary states. Our results agree with profiles obtained within the so-called bag model with very good accuracy, however, not all such solutions are stable and realised in dynamical systems. Depending on the exact shape of the potential there is always a range of wall velocities where no steady state solutions exist. This behaviour in deflagrations was explained by hydrodynamical obstruction where solutions that would heat the plasma outside the wall above the critical temperature and cause local symmetry restoration are forbidden. For even more affected hybrid solutions causes are less straight forward, however, we provide a simple numerical fit allowing one to verify if a solution with a given velocity is allowed simply by computing the ratio of the nucleation temperature to the critical one for the potential in question.

Electroweak corrections to Dark Matter Direct Detection
2023-07-06 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Dark matter direct searches place very stringent constraints on the possible DM candidates proposed in extensions of the Standard Model. There are however models where these constraints are avoided. One of the simplest and most striking examples comes from a straightforward Higgs portal pseudoscalar DM model with a softly broken U(1) symmetry. In this model the tree-level DM-nucleon scattering cross section vanishes in the limit of zero momentum-transfer. Furthermore, adding doublets while keeping the pseudoscalar with the softly broken U(1) symmetry leads to the same result. We have calculated the exact cross section at the one-loop level in two of these scenarios, which is several orders of magnitude larger than the tree-level one. I will also compare these results with scalar DM models where the cancellation at tree-level does not occur. Finally I will present results for a simple model with a vector dark matter particle.

Quantum Field Machines with cold atoms
2023-07-10 10:00 - 12:00 | Online
Resumo Esta tese leva a cabo estudos no campo da termodinâmica quântica, propondo o conceito novo de Máquina de Campo Quântico, desenhada para executar tarefas específicas no domínio quântico. Para descrever completamente o comportamento desta máquina, são necessários conceitos de mecânica quântica e, ao mesmo tempo, ferramentas de física estatística, uma vez que não é viável descrever cada grau de liberdade do sistema individualmente. Tais requerimentos fazem da Máquina de Campo Quântico uma genuina máquina térmica quântica que opera na intersecção da mecânica quântica e da termodinâmica. No contexto deste trabalho, a Máquina de Campo Quântico é um sistema de átomos frios constituído por três componentes. O propósito da MCQ é arrefecer uma destas componentes, usando duas operações básicas (designadas de primitivas) que encontram equivalência na termodinâmica clássica: A primeira operação é a compressão/expansão de uma das componentes (assemelhando-se a um pistão); a segunda operação consiste em acoplar um par de componentes para transferência de energia (assemelhando-se a uma válvula). Neste trabalho, estudamos numericamente cada primitiva, bem como vários ciclos de arrefecimento, resultantes da operação da máquina. Também demonstramos a implementação experimental da prova-de-conceito de cada primitiva. Para isso, usamos condensados de Bose-Einstein unidimensionais gerados na plataforma Atomchip. Além disso, avaliamos ainda as consequências de migrar duas componentes independentes para o regime de acoplamento forte, onde fenómenos como fluxo de calor anómalo podem ser observados. Este trabalho abre caminho para futuras investigações em termodinâmica quântica e oferece ferramentas para estudar termodinâmica com sistemas quânticos e finitos, fora do usual limite termodinâmico.

“Search for top squarks in the four-body decay mode with single lepton final states in proton-proton collisions at the Large Hadron Collider
2023-07-13 14:00 - 16:00 | Online
Resumo:Nesta tese, é a presentada uma pesquisa para a produção de pares do parceiro supersimétrico mais leve do quark top, o squark top (et 1 ). Esta pesquisa tem como alvo o decaimento em quatro partículas do et 1 , que é preferida quando a diferença de massa entre o squark top e a partícula supersimétrica mais leve é menor que a massa do bosão W.Este modo de decaimento consiste em um quark bottom, dois outros fermiões e o neutralino mais leve (χe 0 1 ), que é assumido como sendo a partícula supersimétrica mais leve. Os dados correspondem a uma luminosidade integrada de 138 fb−1 de colisões protão-protão com energia de centro de massa de 13 TeV coletados pela experiência CMS no LHC do CERN. Os eventos são selecionados usando a presença de um jato de alta energia, um eletrão ou muão com baixo momento transverso e um momento transversal em falta significativo. O sinal é selecionado com base em uma abordagem multivariada que é otimizada para a diferença entre m(et 1 ) e m(χe 0 1 ). A contribuição dos principais processos de fundo é estimada a partir dos dados. Nenhum excesso significativo é observado acima da expectativa dos processos do modelo padrão. Os resultados desta pesquisa excluem top squarks com 95% de nível de confiança para massas até 480 e 700 GeV para m(et 1 ) − m(χe 0 1 ) = 10 e 80 GeV, respetivamente.

Quantum Walk Methods for Link Prediction in Complex Networks
2023-07-13 14:00 - 16:00 | Online
Abstract: The problem of link prediction is to identify missing or future connections in a complex network through the structural patterns that emerge in their topology. A common approach uses path structures between nodes, quantifying direct and neighbouring node similarities through a scoring function. Computing the scoring function for every possible node combination can be computationally hard. We design a quantum link prediction algorithm based on continuous-time quantum walks (CTQW), showing that is encodes a scoring function similar to classical path-based link predictions methods. A CTQW is a simple model for quantum dynamics and quantum computation on a graph. Finding applications of quantum computing in complex networks can help speedup network science problems. We further improve our algorithm and describe a sampling-based framework for link prediction. We use a oracle-query access model to the input network and show that the complexity of implementing our quantum algorithm is limited by performing quantum simulation of the network’s adjacency matrix. Considering the quantum simulation of d-sparse matrices, where d is the maximum number of entries in any row or column, we show that there is a polynomial quantum speedup compared to classical sampling algorithms for a fixed number of samples. Despite this speedup, the quantum simulation of d-sparse matrices is not efficient for complex networks due to the existence of some nodes that are densely connected. As a first step towards the efficient quantum simulation of complex networks, we show that a toy network model with mostly sparsely connected nodes and a few densely connected ones can be efficiently simulated. Performing efficient quantum simulation of complex networks could be an important routine for quantum algorithms applied to network science problems in general. Furthermore, in a different research direction, we explore how quantum dynamics may be used for eneregy-efficient classical computation. We design a 1-bit full adder operating with a quantum representation of classical bits using electrons confined in quantum dots, and discuss how the energetic costs of computation could potentially be reduced. In our estimates we find that the energetic cost of cooling would be the main bottleneck of this technology.

New facets of the Penrose process: Black hole bomb with massive particles and particle decay near a naked singularity
2023-07-13 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:We consider the decay of a particle with some energy E_0 > 0 inside the ergosphere of a black hole. After the first decay, one of the particles with the energy E_1 < 0 falls toward the black hole, while the second particle with E_2 > E_0 moves in the outward direction. The second particle bounces back from a reflecting shell and the process repeats itself. For radial motion of charged particles in the Reissner-Nordström black hole spacetime, the result depends strongly on the concrete scenario that one might consider. In particular, an indefinitely large growth of energy inside the shell is possible, such that it gives rise to a black hole bomb. We also consider a similar multiple process with neutral particles in the background of a rotating axially symmetric stationary dirty black hole. We demonstrate that if particle decay occurs in a turning point, the black hole bomb in this case is impossible. For a generic point inside the ergoregion, there is a condition for the black hole bomb to exist. This condition relates the ratio of masses before and after decay and the velocity of the fragments in the center of mass frame. We also analyze a complementary case when the metric represents a naked singularity and show that in this case a super-Penrose process is possible.

Radiative neutrino masses
2023-07-13 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:I will present four models where light active neutrino masses are radiatively generated. In the first one, the tiny active neutrino masses are generated via a three-loop radiative inverse seesaw mechanism, with the Dirac and Majorana submatrices arising at one-loop level. To the best of my knowledge, this is the first example of the inverse seesaw mechanism being implemented with both submatrices generated at one-loop level. The model is consistent with electroweak precision observables, the electron and muon anomalous magnetic moments as well as with the constraints arising from charged lepton flavor violation and the 95 GeV diphoton excess. In the second model, a dark sector seeds neutrino mass generation radiatively within the linear seesaw mechanism and sizeable rates for charged lepton flavor violation are obtained. The third model is a Majoron-like extension of the Standard Model with an extra global U(1)X symmetry where neutrino masses are generated through an inverse seesaw mechanism at the 1-loop level. The model is also consistent with charged lepton flavor violation and dark matter. The fourth one is a minimally extended inert doublet model where the tiny neutrino masses are generated through a three-loop seesaw. The model has viable dark matter candidates and leads to a rich phenomenology while satisfying all the current constraints imposed by neutrinoless double-beta decay, charged-lepton flavor violation, and electroweak precision observables.

Advanced magnetoresistive sensors for a novel barcode reading technology
2023-07-17 10:00 - 12:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)

Modelling solid-state High Harmonic Generation
2023-07-18 13:30 - 15:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
(Online)ResumoO processo de geração de harmónicas de ordem superior (HHG) no estado sólido provocou uma onda de interesse científico devido à perspetiva de criar novas fontes compactas de radiação ultravioleta extrema (XUV) e de aproveitar a dinâmica ultra-rápida dos eletrões em sólidos. A possibilidade de criar materiais com respostas ópticas personalizadas ou métodos de mapeamento da estrutura de bandas totalmente ópticas através de HHG continua a impulsionar esta área de investigação. Estudamos as interações de campo forte que caracterizam HHG em sólidos através de simulações baseadas na teoria do funcional da densidade dependente do tempo (TDDFT), com o objetivo de compreender os processos microscópicos por detrás da geração da radiação harmónica. Em particular, modelamos MgO e β-Ga2O3 em volume, perturbados por impulsos laser de 40 fs no quase- e médio-infravermelho (800 nm e 3 μm), e analisamos a dependência da intensidade das harmónicas na orientação relativa entre o cristal e os eixos de polarização. Adicionalmente, estudamos os efeitos da alteração da elipticidade do feixe nas harmónicos geradas em MgO. Fazemos uma comparação direta com um modelo intra-banda semi-clássico mais simples.Modelamos com sucesso o comportamento dependente do tempo dos eletrões em sólidos e capturamos a transição dos regimes perturbativos para não perturbativos a partir das simulações TDDFT. Os perfis de resposta à polarização encontrados correspondem aos da experiência, e conceptualizamos um ponto de partida para o estudo de quantidades microscópicas a partir de TDDFT em tempo real. A comparação dos resultados simulados com dados experimentais permitir-nos-á compreender e, em última análise, controlar os mecanismos microscópicos da emissão harmónica em sólidos.

Gravitational Waves and the Galatic Pontential
2023-07-19 14:30 - 16:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
Resumo: O progresso rápido e recente da astronomia de ondas gravitacionais tornou necessário modelar fontes cada vez mais complexas. Durante a próxima década, interferómetros de terceira geração e a missão espacial LISA observarão binárias em centros galácticos envolvendo buracos negros supermassivos com milhões de massas solares. O seu sinal diferá substancialmente das mais ``comuns'' binárias de buracos negros de igual massa que têm dominado as detecções de ondas gravitacionais. Medições mais precisas de eventos mais extremos que excitam campos gravitacionais mais fortes podem ter um impacto tremendo em física fundamental, astrofísica e cosmologia. Porém, à escala galáctica, discos de acreção, halos de matéria escura e densas populações de objectos compactos podem interagir gravitacionalmente com corpos em coalescência. O papel que estas estruturas astrofísicas desempenham na evolução e respectiva assinatura de ondas gravitacionais de sistemas binários continua por explorar e estudos prévios dependeram com frequência de aproximações Newtonianas ad-hoc. Nesta tese, pretendemos melhorar este panorama e responder a questões como: podem ambientes de não-vácuo comprometer testes de Relatividade Geral e da natureza de buracos negros? Podemos colocar constrangimentos nas propriedades de ambientes astrofísicos com futuras observações de ondas gravitacionais? Em particular, estudamos como deformações de maré de matéria presente à volta de buracos negros podem mascarar desvios a Relatividade Geral, ou destruir estruturas ``cabeludas'' que poderiam sinalizar a existência de candidatos de matéria escura como campos bosónicos ultraleves. Também exploramos a conexão profunda entre anéis de luz - órbitas fechadas de partículas sem massa - e os modos próprios de oscilação de objectos compactos. Mostramos que, independentemente da presença de um ambiente, o anel de luz controla como observadores distantes vêem matéria a cair num buraco negro, ou como o buraco negro final formado numa colisão relaxa para estacionariedade. Finalmente, desenvolvemos o primeiro framework completamente relativista capaz de estudar emissão de ondas gravitacionais em ambientes de não-vácuo. Aplicamo-lo a binárias de buracos negros galácticas rodeadas por um halo de matéria escura e observamos a conversão entre ondas de matéria e ondas gravitacionais. Este acoplamento resulta em diferenças significativas no fluxo de energia emitido, que poderão ajudar a constrangir as propriedades de distribuições galácticas de matéria. Os nossos métodos podem tornar-se a ferramenta de referência para estudos de efeitos de ambiente em astronomia de ondas gravitacionais e ser implementado em pipelines de análise de dados de colaborações futuras

One class of non-Abelian 4HDM symmetry
2023-07-20 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso (Online)
Abstract:Multi-Higgs-doublet models equipped with global symmetry groups, either exact or softly broken, offer a rich framework for constructions beyond the Standard Model and lead to remarkable phenomenological consequences. Knowing all the symmetry options within each class of models can guide its phenomenological exploration, as confirmed by the vast literature on the two- and three-Higgs-doublet models. Here, we begin a systematic study of finite non-Abelian symmetry groups which can be imposed on the scalar sector of the four-Higgs-doublet model (4HDM) without leading to accidental symmetries. In this work, we derive the full list of such non-Abelian groups available in the 4HDM that can be constructed as extensions of cyclic groups by their automorphism groups. This list is remarkably restricted but it contains cases which have not been previously studied. Since the methods we develop may prove useful for other classes of models, we present them in a pedagogical manner.

Dynamics in UV completions of k-essence
2023-07-20 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In recent years there has been an increased interest in modelling the nonlinear dynamics in theories beyond general relativity. Recent work by different groups has provided a new pathways towards performing numerical relativity simulations in such theories. In this talk, I summarize subset of these ideas and will illustrate them in the context of k-essence, a subset of Horndeski theory. In particular, I will present and example where different extensions (or UV completions) of the theory allow for continuing the evolution past the Cauchy breakdown of the original theory.

Fabrication and characterization of single GaN microwire radiation sensors: assessment of the detection capabilities and radiation resistance
2023-07-21 10:30 - 12:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
Resumo:Microfios de nitreto de gálio são estruturas muito interessantes devido às suas características intrínsecas e, durante a última década, diversos dispositivos optoelectrónicos baseados em microfios de GaN foram demonstados. Sendo um semicondutor com uma elevada resistência à radiação ionizante e estável à altas temperaturas, os microfios de GaN também apresentam um potencial para serem aplicados como sensores de radiação em ambientes extremos. Os microfios têm uma altura até 30 µm e um diâmetro de 2 µm, e devido a geometria e dimensão reduzida, a sua estrutura cristalina é praticamente livre de deslocações. Adicionalmente, na sua configuração casca-núcleo apresenta uma junçao p-n na direcção radial, o que promove a detecção de carga. Neste trabalho, sensores de radiação baseados num único microfio foram fabricados usando diversas técnicas de microfabricação e caracterizados por diferentes técnicas experimentais. Quando irradiados com protões com uma energia de 2 MeV, a corrente eléctrica aumenta até quatro ordens de grandeza relativamente à corrente escura com tempos de resposta inferiores à 20 ms. Para além disto, experiências de carga induzida por feixes de iões (IBIC) permitiram estudar a eficiência de colecção de carga (CCE). Os resultados indicaram valores máximos na ordem dos 30%. Durante a irradiação, verificou-se que até uma fluência de 1x1014 protões/cm2 a modificação das propriedades eléctricas dos sensores é negligenciável. Para fluências mais elevadas a corrente começa a diminuir, com uma queda mais abrupta entre 5x1014 protões/cm2 e 1x1015 protões/cm2 . No entanto, mesmo após irradiar os dispositivos com uma fluência de 5x1015 protões/cm2 , os sensores continuam a mostrar uma resposta à radiação incidente. Tendo em conta as vantagens inerentes dos microfios, nomeadamente no que toca à possibilidade de detectar radiação ionizante e boa estabilidade, verifica-se o seu potencial na aplicação em diversos campos onde se requer sensores com uma sólida resistência à radiação ionizante.

“Quantum algorithms: from large-scale pattern reconstruction to restricted-depth computation
2023-07-25 09:30 - 11:00 | Online
Resumo:Os algoritmos quânticos aproveitam leis da física quântica para obter uma vantagem de complexidade comparativamente com estratégias clássicas de computação. Nesta tese, apresentamos uma sucessão de trabalhos sobre algoritmos quânticos. Mostramos como acelerar métodos computacionais clássicos com processadores quânticos, desenvolvemos soluções quânticas para problemas de análise de dados, generalizamos uma técnica de simulação de passeios quânticos, reinterpretamos uma interpolação algorítmica clássico-quântica e executamos simulações em computadores quânticos reais.Um dos principais temas desta tese e acelerar métodos de reconstrução de padrões com processadores quânticos. Desenvolvemos algoritmos quânticos para recuperar padrões escondidos em dados com estrutura de grafos. Estudamos o problema de tracking no contexto de experiências de física de partículas e demonstramos como acelerar um método comum de tracking com técnicas de amplificação de amplitude; propomos uma versão quântica do algoritmo density peak clustering; e desenvolvemos um algoritmo quântico baseado em caminhos para previsão de ligações em redes complexas. Relacionado com o problema de previsão de ligações, mostramos que existe um eficiente algoritmo de simulação de passeios quânticos para grafos que são esparsos a exceção de um número pequeno de hubs.O outro tema e entender como obter speedups quânticos num futuro próximo, enquanto os computadores quânticos continuarem extremamente vulneráveis a ruído. Procuramos abordagens algorítmicas teóricas para reduzir as profundidades dos circuitos, de forma a expor a computação a menos ruído. Analisamos um trade-off entre o speedup quântico e profundidade do circuito para o problema de estimação de fase, revelando que este pode ser entendido no contexto do formalismo das transformações quânticas de valores singulares. Também aplicamos uma ferramenta moderna de super-resolução, a “Minimização da Norma Atómica”, a um problema quântico de muitos corpos e mostramos que podemos reduzir significativamente a profundidade dos circuitos envolvidos comparativamente com as técnicas usuais de processamento de sinal.

Signals of new heavy scalars in the flavor-aligned 2HDM
2023-07-27 16:00 - 18:00 | Anfiteatro VA1, Pavilhão de Civil, Piso -1
Abstract:Searches for new neutral Higgs bosons of an extended Higgs sector at the LHC can be interpreted in the framework of the two-Higgs doublet model. By employing generic flavor-aligned Higgs?fermion Yukawa couplings, we propose an analysis that uses experimental data to determine whether flavor alignment is a consequence of a symmetry that is either exact or at most softly broken. Our proposal is illustrated in two different scenarios based on a few 3 sigma (local) excesses observed by the ATLAS and CMS Collaborations in their searches for heavy scalars at Run 2 of the LHC.

Arbitrarily non-paraxial electromagnetic wave-packets in particle-in-cell codes
2023-07-28 09:30 - 11:00 | Sala C10, Pavilhão Central, Piso 1, Campus da Alameda
Resumo Os algoritmos de injeção de lasers normalmente usados em códigos de particle-in-cell (PIC) baseiam- se em soluções analíticas da equação de onda paraxial sob a aproximação de envelope lento. Estes algoritmos são computacionalmente muito eficientes, uma vez que dependem de soluções puramente analíticas. Além disso, são ideais para descrever lasers em que o tamanho do foco e a sua duração temporal são muito maiores que o comprimento de onda e o período, respetivamente. No entanto, estes algoritmos falham ao descrever a estrutura dos campos eletromagnéticos de pulsos de laser ultra curtos (por exemplo, de ciclo único) ou ultra focados, os quais são de elevada importância para a física a altas energias. Neste trabalho, descrevemos um novo algoritmo de injeção de laser o qual se mostra capaz de injetar com precisão estruturas de luz mais complexas em códigos PIC. O algoritmo foi desenvolvido para funcionar em coordenadas 2D e 3D cartesianas e também cilíndricas, satisfazendo exatamente as Equações de Maxwell. É também capaz de injetar qualquer polarização (linear, circular, elíptica, radial e azimutal) e de executar transformações de Lorentz arbitrárias. Usando esta nova injeção, uma nova descrição teórica e numérica de acoplamentos espaço-temporais em pacotes de ondas eletromagnéticos é desenvolvida, permitindo a injeção de pulsos com velocidades focais arbitrárias, conhecidos como pulsos flying focus. Este trabalho unifica duas descrições existentes dessa classe de pacotes de ondas e inclui algumas simulações iniciais de interação entre estes pulsos e plasmas de baixas densidades.

SEMANA DE ACOLHIMENTO DOS NOVOS ALUNOS DA LEFT
2023-09-07 14:00 - 16:00 | Pavilhão de Matemática, Anfiteatro PA1, piso -1

Results of Supernovae sample studies and its implications for theoretical modeling
2023-09-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Supernovae (SNe) explosions mark the explosive death of a star. They are classified empirically based on their observed spectral and light curve features. These features can be connected to the progenitor star to derive pre-explosion characteristics. Some of the pre-explosion characteristics are straight-forward (e.g: if there is hydrogen in the spectra, the progenitor star should have retained its hydrogen layers during its whole evolution). Some are derived through theoretical models (e.g: if the spectra shows broad and boxy hydrogen lines without absorption components, it is possibly due to interaction of the SNe ejecta with a dense shell formed by circumstellar material accumulated during the explosion). Theoretical models are not only useful to infer progenitor properties but also to predict what type of compact remnant will be produced by the explosion, if any. Thus, SNe characterization is of key importance to understand both stellar evolution and the birth of compact objects. In this talk I will present the observational analysis done in samples of different types of SNe and the implications of the results for theoretical models. I will finish by presenting the possibilities and challenges that the new LSST survey presents for the field.

The role of ion channels in the transmissions of signals along axons
2023-09-12 10:00 - 12:00 | Online
ResumoNeste trabalho, propomos um modelo eletrofisiológico bidimensional que descreve a resposta dos neurónios ao serem estimulados em condições de patch-clamp. Este modelo - uma versão reduzida do modelo de Hodgkin-Huxley - conserva as características essenciais da abordagem original, sendo, no entanto, mais eficiente e informativo.Através da análise dos diagramas de bifurcação de diversos modelos reduzidos, descrevemos as contribuições dos diferentes canais iónicos na estabilidade ou instabilidade da membrana neuronal. Para além disso, exploramos a influência que a intensidade dos estímulos elétricos e vários parâmetros celulares têm na frequência de spiking dos neurónios.Também nesta tese, apresentamos um modelo do axónio que simula a transmissão unidirecional de sinais e que não é afetado por perturbações no potencial da membrana. Após analisar o impacto da resistência intracelular e da capacitância membranar na velocidade do sinal, observamos discrepâncias consideráveis entre os nossos resultados e os previstos pela equação de cabo (cable equation model).A nossa investigação revela também que, quando a propagação do sinal ocorre sob a forma de múltiplos picos no potencial da membrana do axónio, há um transiente nos seus comprimentos de onda e frequências, sendo esse transiente influenciado pela resistência intracelular. Consequentemente, os picos têm velocidades distintas, sendo o primeiro pico mais rápido que os restantes. Concluímos também que a velocidade de propagação do primeiro pico - em alguns casos o único - se mantém relativamente constante ao longo do axónio, independentemente da intensidade do estímulo a que o neurónio está sujeito. O mesmo não se observa em picos subsequentes.

Simulating Gauge Theories: Bridging the Gap Between Classical and Quantum Simulations
2023-09-13 14:30 - 16:00 | Physics Seminar Room - Physics Building - 2nd floor (2-8.3)
Abstract:Quantum field theories at strong coupling, as in Quantum Chromodynamics (QCD),require a non-perturbative approach. Lattice discretizations and simulations providesuch an approach, which has achieved remarkable success. This is the case, forexample, of QCD at zero chemical potential. However, in cases like at finite chemicalpotential or under real-time evolution, the best techniques are still hindered by theso-called sign problems.The emergence of quantum simulators for gauge theories,which aim to simulate these theories directly on quantum devices, opens up apromising new avenue for tackling these challenges. Rather than eliminating the needfor classical computational approaches, the latter becomes crucial for validatingquantum simulators and as probes of quantum supremacy. This talk will delve intoboth classical and quantum approaches to tackling these problems. In particular, wewill discuss the basic requirements needed for quantum simulating gauge theories,how they call for new classical approaches, and how all of these open the door to theexploration of new physics. By bridging the gap between classical and quantumapproaches, we aim to advance our understanding of physics at a fundamental leveland pave the way for future advancements in simulating gauge theories.

Sensing and Communication with Quantum Microwaves
2023-09-14 14:00 - 16:00 | Online

Tidal effects in compact object binaries and why they matter
2023-09-14 14:30 - 16:00 | Sala de Reuniões e Seminários (2-8.3) 2º Piso Pavilhão de Física
Abstract:The field of gravitational wave astronomy is allowing us to study the nature of compact objects in binary systems through their gravitational wave emission. Namely, the tidal deformability of such objects, encoded in their tidal Love numbers (TLNs) gives us a window into their composition and the physics behind them. However, the increasing accuracy of future gravitational wave detectors will likewise require a more accurate modeling of the emitted waveforms, and therefore a more detailed study of TLNs. In my talk, I will present recent advances on how the spin of a compact object affects its TLNs. I will also discuss the impact these spin-tidal effects will have on future gravitational wave detections, focusing on neutron star binaries, as well as other (dynamical) tidal effects and their possible relevance in the near future.

Let's talk about... Ultrafast Physics
2023-09-14 17:00 - 19:00

Ultrafast Mid-Infrared Tunable Laser Sources
2023-09-19 09:00 - 11:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
Os lasers de alta potência e impulsos ultra-curtos na região do infravermelho médio (IR-médio, ~3—8 μm) têm atraído crescente interesse da comunidade laser na última década, devido às suas aplicações em importantes áreas como física de campo intenso. Em comparação com sistemas ultra-curtos com dimensões na escala de metros no IR-próximo, os lasers de IR-médio têm um potencial maior para gerar harmónicas mais altas, suportando durações extremamente curtas na ordem de poucos attossegundos, devido à extensão da energia de corte com o comprimento de onda do laser instigador do processo. Um esforço significativo tem sido colocado no desenvolvimento e refinamento desta tecnologia, levando a vários avanços científicos. No entanto, o dimensionamento destes sistemas para atingir energias no nível do mJ é ainda um desafio elevado devido à quantidade limitada de materiais transparentes e dispositivos no IR-médio, normalmente caracterizados por limiares de dano mais baixos e perdas mais altas. A escassez de lasers ultra-curtos de estado sólido no domínio espectral de IR-médio limitam a geração de impulsos energéticos a técnicas não-lineares, como a Amplificação Paramétrica Óptica de Impulsos Chirpados (OPCPA). Estes métodos permitem não só a capacidade fundamental de amplificação de banda larga, mas também permitem uma ampla sintonização de banda, o que os torna ainda mais atrativos. Nesta tese, investigamos e avaliamos a estratégia ideal para atingir impulsos de poucos ciclos na ordem do mJ no infravermelho médio, apresentando o trabalho realizado com três sistemas diferentes motivados pela sua capacidade em gerar impulsos próximos ou na região de infravermelho médio. O trabalho descrito inclui: (i) optimização, caracterização e compressão do sistema OPCPA já em operação com impulsos auxiliares próximos da região do infravermelho médio. (ii) Estudos numéricos para geração de impulsos ultra-curtos de alta energia no infravermelho médio usando cristais não lineares para OPCPA de banda ultra-larga. Avaliamos várias alternativas para obter impulsos altamente energéticos de 3 μm com alto ganho e eficiência, em estágios simples e múltiplos. (iii) Dimensionamento de uma OPCPA no infravermelho médio para alcançar impulsos de poucos ciclos e de multi-mJ através da extensão das capacidades do sistema de laser no L2I/IST. Discutimos os passos para a implementação de um novo sistema de impulsos de 3 μm, ultra-curtos (5 ciclos ópticos) e de alta energia (5 mJ), e analisamos os principais desafios. (iv) Compressão de impulsos de alta energia na região do infravermelho médio. Avaliamos detalhadamente a compressão de diferentes impulsos no infravermelho médio gerados pelo sistema OPCPA nas instalações do AUO-ICFO. Potencial para atingir impulsos tão curtos quanto 55 fs a 7 μm, correspondendo a 2,4 ciclos, é demonstrado através da auto-compressão em materiais finos.

A novel treatment planning method for proton FLASH radiotherapy: Combining FLASH with VMAT
2023-09-19 14:00 - 16:00 | Online
In this work, we propose a new treatment planning method for multi-beam FLASH radiotherapy (Stitching FLASH) that combines FLASH delivered by proton beams, with volumetric modulated arc therapy (VMAT). The Stitching FLASH method requires the target to be divided into different sections. For sections close to an Organ-at-risk (OAR), proton FLASH beams were used to deliver radiation dose. For the remaining target volume, VMAT was used to achieve optimal target coverage. To validate the Stitching FLASH method, we used matRad, a treatment planning toolkit developed by DKFZ. We applied it first, as proof of concept, to irradiate three spherical phantoms surrounded by several OARs and second, to irradiate a cervical spinal cord tumor, which we then compared to the clinical VMAT plan. In our phantoms study, we managed to fulfil the minimum dose and dose-rate conditions for protecting the OARs with FLASH, while obtaining excellent target coverage and superb dose conformity and homogeneity. For the spinal cord tumor irradiation, we were able to significantly increase the Clinical Target Volume (CTV) coverage and minimum dose, while keeping the doses in the OARs below the clinical thresholds using the FLASH protecting effect. With the novel FLASH treatment planning method proposed in this work, we have demonstrated that it is possible to protect critical OARs, while maintaining excellent target coverage and dose homogeneity, as well as conformity. This shows that the Stitching FLASH method is promising for proton FLASH radiotherapy

Let's talk about... Neutrinos
2023-09-21 17:00 - 19:00

Modelling of Alfvén modes and their stability in the presence of ICRH-accelerated energetic ion populations in tokomak devices
2023-09-22 09:00 - 11:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
Resumo: Os plasmas de fusão encontrados em reactores tokamak são em grande extensão descritos com sucesso pelo modelo da Magneto-hidrodinâmica (MHD). Este modelo prevê a existência de modos de Alfvén discretos que são facilmente excitáveis através da interacção ressonante com populações de iões energéticos. Esta interação pode levar ao crescimento exponencial dos modos e não só comprometer a operação auto-sustentada dos reactores como também resultar em danos a alguns dos seus componentes. É, portanto, de extrema importância que se desenvolvam métodos para controlar estes modos durante a operação de reactores de fusão. Nesta tese, dois tipos de modos de Alfvén são estudados através de modelação numérica: as cascatas de Alfvén e os TAEs (do inglês Toroidicity-induced Alfvén Eigenmodes). Os estudos foram conduzidos com dois objectivos principais: perceber a relação destes modos com parâmetros do equilíbrio tais como o perfil do factor de segurança, de forma a identificar detalhes do equilíbrio que podem ser inferidos através da observação dos modos em descargas (processo conhecido como espectroscopia MHD); contribuir para o desenvolvimento de métodos para controlar o aparecimento e crescimento destes modos. Os estudos apresentados nesta tese contribuíram para a identificação numérica de diversos tipos de cascatas observadas em descargas do Joint European Torus (JET). Em particular, foram identificadas cascatas de alta frequência com padrões de frequência decrescente e, pela primeira vez no JET, cascatas próximas do eixo magnético associadas a perfis monotónicos quase planos. Adicionalmente, a transição de modos cascata para TAEs foi investigada, de onde resultou a proposta de um método de espectroscopia MHD para estimar a evolução do factor de segurança. É ainda apresentada nesta tese a análise de uma experiência dedicada à supressão de TAEs utilizando a tecnologia de geração de corrente através da ressonância ciclotrónica dos electrões (Electron Ciclotron Current Drive – ECCD). Estimativas dos efeitos de excitação e atenuação experienciados pelos modos indicam que a supressão dos modos está maioritariamente relacionada com o decréscimo da excitação por parte de uma população de partículas rápidas.

Pentaquark Spectroscopy in a Bethe Salpeter Approach
2023-09-25 14:00 - 16:00 | Online (Meeting-ID: 624 9382 9561 Password: [REDACTED]
Abstract:One of the spectacular successes of this millennium's hadron spectroscopy experiments is the discovery of many exotic meson states in the heavy-quark energy region, which do not seem to fit into the conventional quark model picture. Our traditional understanding of hadrons is that they can be grouped into mesons (quark-antiquark states) and baryons (which are made of three valence quarks). Moreover, over the last years the LHCb collaboration has found prominent peaks in the J/ψ-proton invariant mass spectrum. This implies a minimal quark content uudc-cbar and thus constitutes the first clear experimental evidence for pentaquarks. The proximity of those peaks to meson-baryon thresholds suggests a molecular explanation in terms of meson-baryon molecules, in analogy to several exotic meson candidates in the charmonium sector.The goal of this PhD project is to establish a theoretical description of pentaquarks from a covariant five-body Bethe-Salpeter equation in QCD, namely as five-body systems made of four quarks and one antiquark where the (anti-)quarks interact through gluons. This is based on a body of preceding work on mesons, baryons and tetraquarks from 2-, 3- and 4-body equations, which have been successful in describing the spectra and internal dynamics of these states. Therefore, the generalization of the approach to the five-body problem will substantially advance the status quo and deliver predictions on the spectrum and structure of pentaquarks directly from QCD.In this seminar, I will mainly focus on three works: I will present the technical basis for treating the five-body equation for a scalar system, which provides the starting point for detailed studies in view of the resonance behavior of pentaquarks, their internal structure, and also light-quark spectroscopy to investigate meson-cloud effects on baryons. I will also present the ongoing work on the five-body equation using the leading tensor components. Secondly, I will present the two-body equation for a pentaquark as a meson-baryon system and describe how the Dyson-Schwinger and Bethe-Salpeter equations work. Finally, I will briefly discuss another project I have been working on, namely the QCD contributions to flavor changing neutral currents which may pose constraints on flavor anomalies.

R&D: Radiation Hardness of Plastic Scintillating Materials for Scintillator Calorimeters
2023-09-27 10:00 - 12:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
In the quest to advance the field of high-energy physics, future experiments demand particle detectors that meet specific key factors on the roadmap for their success. In the case of scintillator-based calorimeters or other detectors using scintillators, the requirements are: high light yield, fast signals, dual readout capability, high granularity, and radiation hardness. These criteria provide the foundation for breakthroughs in particle physics, necessitating the exploration of innovative scintillator materials. Currently, one of the most cost-effective options for particle detection is plastic scintillators. These materials possess the unique property of producing scintillation, detectable photons in the visible part of the light spectrum, upon interaction with ionizing radiation or charged particles. Additionally, they offer an exceptionally rapid light signal and a high light response. However, scintillator plastics undergo natural material degradation, particularly in radiation-rich environments. Hence, identifying materials with enhanced radiation resistance is crucial for advancing high-energy physics experiments. Polyethylene Naphthalate (PEN) and Polyethylene Terephthalate (PET) emerge as promising candidates for the development of new scintillator materials. Preliminary studies suggest that PET exhibits superior radiation resistance, while PEN demonstrates a higher light response compared to PET. Significantly, both PEN and PET scintillate without the need for dopants. This context underscores the importance of investigating the feasibility of PEN/PET as fundamental materials for innovative scintillator plastics, aligning seamlessly with the demands of future high-energy physics experiments. The primary objectives of this research project are develop cost efficient plastic scintillators with competitive characteristics to the existing ones, in terms of light yield and transparency and develop competitive radiation hard scintillators This encompasses the development and characterization of new scintillating plastics, with initial focus on PEN and PET as well as characterisation of commertial ones (for comparison). Furthermore, we aim to assess the materials' response to radiation exposure. Modeling the effects of various dose rates on the materials' radiation hardness will also be a significant aspect of our study. This research project is developed in collaboration with the Institute of Polymers and Composites (IPC) from the University of Minho, who can produce plastic scintillators with different compositions. In this presentation, we will show preliminary results regarding the production and characterization of these samples, encompassing aspects such as light response, emission spectra, and transmittance spectra. Additionally, we will describe the irradiation planning for the samples and the simulation developed for comparing the light response between the samples and reference measurements.

Bragg Peak monitoring through prompt-gamma: detection and instrumentation
2023-09-27 14:00 - 16:00 | Sala de seminários do LIP
Abstract:The primary goal is the development of the instrumentation for an Orthogonal Prompt-Gamma Imaging (OPGI) detector for range verification in Proton Therapy treatments.The experimental program includes tests with small scale prototypes to assess the signal output and to develop preliminary instrumentation to deal with a low number of channels. Crystals read by SiPM devices were used to acquire waveforms for analysis. Simultaneously, simulations were developed to study the performance of the system and to study possible enhancements to the system, namely the light collection system. A solution for a large number of channels will be tested in the near future.

Chiral qubit basis and eigenstates of spin chains with nontrivial topology
2023-09-27 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Phantom Bethe excitations in integrable spin chains (XXZ,XYZ Heisenbergmodel) generate eigenstates with nontrivial topology, a spin helix statebeing a representative. I will show that it is natural to describe thesetopological states with chiral basis instead of the computational basis. Wepropose an orthonormal basis for qubits, and demonstrate its usage for anexperimentally relevant problem in cold atoms.

Scattering in the interior of black holes and the cosmic censorship conjecture
2023-09-28 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:Scattering theories are of large importance for many problems in General Relativity, and scattering in the interior of a black hole is particularly relevant in the context of the cosmic censorship conjecture and the related Cauchy horizon instability problem. The Cauchy horizon instability is thought to be directly linked to a notion of gravitational blue-shift at the horizon, which manifests itself as a blow-up in some observed quantity. By constructing the scattering channels, one aims to recover information about the behavior of the field near the horizons, where the instabilities might be seen as the unboundedness of the scattering operators (energy blow-up) or from the lack of regularity at the horizon of the propagating field (C^1-blow-up). In this talk I will present the recent development of the scattering theories in the interior black holes between the Cauchy horizon and the event horizon, and the various blow-up results. From a mathematical point of view, different fields exhibit contrasting scattering phenomena. For example, the scattering of linear waves is delicate and surprising breakdowns of scattering happens in generic situations.

Let's talk about... Numerical Relativity!
2023-09-28 17:00 - 19:00

Signatures of dissipative quantum chaos
2023-10-06 14:30 - 16:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
Resumo: Compreender a dinâmica fora do equilíbrio de sistemas quânticos dissipativos, onde a dissipação e a decoerência coexistem com a dinâmica unitária, é um enorme desafio. Frequentemente, a única abordagem realista é renunciar a uma descrição microscópica detalhada e, ao invés, procurar por assinaturas de comportamento universal partilhadas por conjuntos de sistemas complexos distintos mas suficientemente semelhantes. O caos quântico fornece o enquadramento estatístico para abordar esta questão, recorrendo a simetrias para obter informação não acessível de outra forma. Esta tese examina como conciliar caos com dissipação, procedendo ao longo de duas linhas complementares. Na Parte I, aplicamos a teoria das matrizes aleatórias não-Hermíticas a sistemas quânticos abertos com dissipação Markoviana e discutimos as escalas de tempo de relaxação e estados estacionários de três exemplos representativos com crescente relevância física: Lindbladianos e mapas de Kraus de uma partícula, fermiões livres abertos e modelos de Sachdev-Ye-Kitaev (SYK) dissipativos. Para sistemas com caos quântico a um corpo, estabelecemos a universalidade dos seus estados estacionários. Para o modelo SYK com interações fortes, descobrimos que o relaxamento é dominado pela dissipação no regime de dissipação forte e dominado pelo caos, com um hiato anormalmente grande, no regime de dissipação fraca. Na Parte II, investigamos as simetrias, correlações e universalidade de sistemas quânticos abertos de muitos corpos, classificando vários modelos de matéria quântica dissipativa. Usamos o Hamiltoniano SYK não-Hermítico como um modelo simplificado prototípico com não só um estado estacionário ergódico universal mas também propriedades não universais, mas ainda genéricas, de sistemas dissipativos quânticos de muitos corpos na sua aproximação à ergodicidade. Além disso, vamos além dos Hamiltonianos não-Hermíticos efetivos e consideramos a classificação de simetria dos Lindbladianos de muitos corpos. Encontramos uma classificação com dez classes na ausência de simetrias unitárias, realizada em modelos realistas de cadeias de spin, a qual pode ser enriquecida por simetrias unitárias. Em todos os exemplos, investigamos as correlações espectrais e confirmamos que elas são descritas pela teoria das matrizes aleatórias—o traço distintivo do comportamento caótico quântico. Do ponto de vista teórico, esta tese desenvolve um enquadramento genérico para o estudo das propriedades universais de sistemas quânticos realistas, caóticos e dissipativos. Do ponto de vista prático, fornece as componentes para a construção de evoluções dinâmicas dissipativas restringidas por simetrias, com potencial impacto tecnológico na fabricação de estruturas quânticas complexas

ICECUBE: The Under-the-ice Neutrino Observatory in Antarctica. Opening a New Window on the Universe from the South Pole
2023-10-09 17:00 - 19:00 | Centro de Congressos ( -2 Floor of Civil Building)
Abstract:The IceCube project at the South Pole melted 86 holes 2.5 kilometer deep in the Antarctic icecap to construct an enormous astronomical observatory. The experiment discovered a flux of neutrinos from deep space with energies more than a million times those of neutrinos produced at accelerator laboratories. These cosmic neutrinos are created in some of the most violent processes in the universe since the Big Bang and originate in the cosmic particle accelerators that are still enigmatic sources of cosmic rays. This lecture will discuss the IceCube neutrino telescope and the discovery of high-energy neutrinos of cosmic origin. It will highlight the recent discovery that high-energy neutrinos—and cosmic rays—originate in sources powered by rotating supermassive black holes.

General relativistic solutions in minimal theory of bigravity
2023-10-12 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: We investigate dynamical properties of static and spherically symmetric systems in the self-accelerating branch of the Minimal Theory of Bigravity (MTBG). In the former part, we study the gravitational collapse of pressure-less dust and find special solutions, where, in both the physical and fiducial sectors, the exterior and interior spacetime geometries are given by the Schwarzschild spacetimes and the Friedmann-Lemaitre-Robertson-Walker universes dominated by pressure-less dust, respectively, with specific time slicings. In the case that the Lagrange multipliers are trivial and have no jump across the matter interfaces in both the physical and fiducial sectors, the junction conditions across them remain the same as those in general relativity (GR). For simplicity, we foliate the interior geometry by homogeneous and isotropic spacetimes. We find interesting classes of exact solutions that represent gravitational collapse in MTBG. In the spatially-flat case, under a certain tuning of the initial condition, we find exact solutions of matter collapse in which the two sectors evolve independently. In the spatially-closed case, once the matter energy densities and the Schwarzschild radii are tuned between the two sectors, we find exact solutions that correspond to the Oppenheimer-Snyder model in GR. In the latter part, we study odd-parity perturbations of the Schwarzschild-de Sitter solutions written in the spatially-flat coordinates. For the higher-multipole modes $\ell\geq2$, we find that in general the system reduces to that of four physical modes, where two of them are dynamical and the remaining two are shadowy, i.e., satisfying only elliptic equations. In the case that the ratio of the lapse functions between the physical and fiducial sectors are equal to a constant determined by the parameters of the theory, the two dynamical modes are decoupled from each other but sourced by one of the shadowy modes.Otherwise, the two dynamical modes are coupled to each other and sourced by the two shadowy modes. At least for the cases of collapse described in this paper, we find that the ratio of the lapse functions is determined by the properties of the collapse itself. On giving appropriate boundary conditions to the shadowy modes as to not strongly back-react/influence the dynamics of the master variables, in the high frequency and short wavelength limits, we show that the two dynamical modes do not suffer from ghost or gradient instabilities.

Let's talk about... Nanophotonics!
2023-10-12 17:00 - 19:00

CORRELATIONS IN QUASI-PERIODIC STRUCTURES
2023-10-13 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The present research plan aims at understanding the interplay between incommensurability and electronic interactions in systems with different dimensionalities, including 1D quasiperiodic systems (QPS) and 2D moiré structures, such as twisted bilayer graphene (tBLG).Currently, there is not much overlap between the low-dimensional systems community and that dealing with incommensurability effects. In 1D QPS, the effects of incommensurability on localization and transport properties are well established, whereas they are almost completely neglected in most theoretical studies related to 2D moiré systems. Conversely, the study of moiré physics, such as the formation of narrow-bands and the associated exotic correlation phenomena, is overlooked in 1D QPS. By studying the interplay between incommensurability and interactions, we intend to bridge this gap and provide insights into the superconducting and correlated phases in tBLG. Our results will be of interest to other systems where incommensurate structures can naturally appear or be induced, such as other twisted layered compounds and optical lattices.

Utilizing novel enhancement principles to develop high performance thermoelectrics
2023-10-19 11:00 - 13:00 | CTN Auditorium
AbstractDevelopment of thermoelectric (TE) materials is important, for energy saving via waste heat power generation [1], and IoT power sources [2]. For high TE performance, tradeoffs must be overcome, between Seebeck coefficient S and electrical conductivity s, and between electrical and thermal conductivity k [3]. For the latter, in addition to nanostructurings, intrinsic low k mechanisms: Materials informatics approach [4], doping leading to lattice softening [5], heterogeneous bonding from mixed anions [6], etc. For the first tradeoff, magnetism can be utilized to enhance S via magnon drag in CuFeS2 [7] and metastable Fe2VAl-based thin films [8,9], paramagnon drag in CuGaTe2 [10], Bi2Te3 [11] etc., Spin fluctuation [12], Spin entropy [13]. Recently, striking Cu doping effect in Mg3Sb2 : interstitial Cu doping lowered the phonon group velocity, while doping into the grain boundaries led to very high mobilities similar to single crystals, while being low k polycrystalline. An initial realistic 8-pair module exhibited efficiency of 7.3%@320oC, while estimated material efficiency ~11%! [14]. Tuning toward RT yielded 8-pair module with efficiency of 2.8%@100oC and cooling of 56.5 K [15]. Recently, a single element device of doped Mg3Sb2 achieved efficiency ~12% [16].[1] L. E. Bell, Science 321, 1457 (2008), JOM, 68, 2673 (2016). [2] Sci. Tech. Adv. Mater. 19, 836 (2018), MRS Bull., 43, 176 (2018). [3] T. Mori, Small 13, 1702013 (2017), Energies, 15, 7307 (2022). [4] Energy Environ. Sci., 14, 3579 (2021). [5] Adv. Energy Mater., 11, 2101122 (2021). [6] J. Mater. Chem. A, 9, 22660 (2021), J. Mater. Chem. A, 11, 10213 (2023) Hot article. [7] Angew. Chem. Int. Ed. 54, 12909 (2015). [8] Phys. Rev. B, 104, 214421 (2021). [9] Nature 576 (7785) 85 (2019). [10] J. Mater. Chem. A, 5, 7545 (2017). [11] Mater. Today Phys., 9, 100090 (2019). [12] Science Adv., 5, eaat5935 (2019). [13] Sci. Tech. Adv. Mater., 22, 583 (2021).[14] Joule, 5, 1196 (2021). [15] Nature Commun., 13, 1120 (2022). [16] Adv. Energy Mater., doi: 10.1002/aenm.20230166 Selected as Front Cover Article.

Living with ghosts: stable edition
2023-10-19 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: I will discuss our recent works Phys.Rev.Lett. 128 (2022) 4, 041301 and ePrint: 2305.09631. There we presented a large class of mechanical models where a canonical degree of freedom interacts with another one with a negative kinetic term, i.e., with a ghost and yet the system is totally stable. We proved analytically that the classical motion of the system is finite i.e. Lagrange stable for all initial conditions, notwithstanding that the conserved Hamiltonian is unbounded from below and above. Moreover, there are Lyapunov stable equilibrium configurations. Numerical computations fully supported this. Systems with negative kinetic terms often appear in modern cosmology, quantum gravity, and high energy physics and are usually deemed as unstable. Our result demonstrates that, for mechanical systems, this common lore can be too naïve and that a stable living with ghosts is possible.

Let's talk about... From plasmas to cold matter
2023-10-19 17:00 - 19:00

Evaluating the Effectiveness of Mini-Beam Radiation in Cancer Therapy
2023-10-20 09:30 - 11:00 | Online (Password: [REDACTED]
Main aim: To investigate the mechanisms triggering the FLASH effect and the possibility of combination of FLASH and mini-beam techniques in Cancer Therapy.In recent years irradiations with ultra-high dose rates (FLASH) have garnered attention due to the increased differential response between normal tissue and cancer. The FLASH effect is characterized by the radioprotection of the healthy tissue while persevering the clinical tumor control achieved by conventional radiotherapy, but the mechanisms that may lead to the flash effect FLASH are being investigated.In this work, the properties of the chemical species generated through the radiolysis of water are investigated as a possible surrogate of the FLASH effect. The modeling perfomed will then be applied to the investigation of the combined application of FLASH and mini-beams to Cancer therapy.

The cylinder at spatial infinity and asymptotic charges
2023-10-20 14:30 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1
Nesta tese, são calculadas as constantes Newman-Penrose (NP) para um campo de spin-0 propagando no espaço-tempo de Minkowski, com ênfase no comportamento próximo ao infinito espacial e ao infinito nulo. Para alcançar isso, é utilizada a estrutura do i^0 cilindro de Friedrich. Sob a suposição de que os dados iniciais atendem a determinadas condições de regularidade, permitindo a extensão analítica do campo para conjuntos críticos, o estudo revela que as constantes NP no infinito nulo futuro I^ + e no infinito nulo passado I^ − são independentes uma da outra. Noutras palavras, as constantes NP clássicas em I ^± são determinadas por partes diferentes dos dados iniciais, que são definidos em uma hipersuperfície de Cauchy. Por outro lado, ao introduzir uma pequena generalização conhecida como constantes NP do i^0 cilindro, a necessidade da condição de regularidade é eliminada. Estas constantes NP modificadas fornecem quantidades conservadas em I^ ± que são exclusivamente determinadas por uma parte específica dos dados iniciais, que, por sua vez, correspondem aos termos que governam a regularidade do campo. Esta característica mostra-se fascinante no estudo de equações de evolução usando a estrutura do i^0 cilindro.

New Radiobiological and Nanodosimetric Insights into Proton Therapy
2023-10-23 17:00 - 19:00 | Online (ID da reunião: 978 2912 4525 Senha: [REDACTED]
Main aim:Establish a new concept of radiation quality, describing the radiation by physical quantities that are related to the particle track structure at the nanometre level. Characterisation of particle track structure is based on the frequency distribution of the size of ionisation clusters – Ionisation Cluster Size Distribution - and associated parameters.

In vivo dosimetry for hadron therapy: Gadolinium as a surrogate for dose measurements
2023-10-25 11:00 - 13:00 | Online (Password: [REDACTED]
Abstract:The feasibility of using a Gd-based contrast agent as mean of in vivo dosimetry was explored up until now in the scope of the project. The characteristic x-ray peak of Gd (ca 43 keV) was studied under several scenarios to access the possibility of using it as a surrogate for in vivo and in real time dose measurements. The dose and dose rate dependence of the Gd signal was experimentally verified. An increase of the Gd x-ray peak height was observed for increasing deposited doses at the target and a decrease in the signal was measured for increasing dose rates. Several other variables, such as medium attenuation, angle of detection and concentration of Gd in the tumor volume were researched in order to understand their impact in the response of the dosimeter. Finally, the dosimeter was tested in a scenario that aimed to simulate a treatment plan subjected to uncertainties (in this case coming from movements of the target, either by inter-fraction displacement, intra-fraction organ motion or overall change in the patient anatomy). A correlation between the x-ray Gd signal and the amount of irradiated volume was observed, which makes it possible to track spatial changes in the deposition of dose.For in depth displacements of the target, a dependence with the energy of the incident particles was observed, not being possible to access any correlation between Gd x-ray signal and total dose at the target. The physics behind the secondary emission of the x-rays of interest was also studied and it was seen that several processes are in the origin of the observed signal, mainly particle induce x-ray emission and neutron capture events.

Gravitational radiation in full general relativity with a non-negative cosmological constant
2023-10-26 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: A covariant, gauge-invariant criterion for the existence, or absence, of gravitational radiation at infinity with non-negative cosmological constant (Lambda) is presented. For Lambda>0, the fundamental idea is that the physical asymptotic properties are encoded in {I,h,D}, where I is a three-dimensional manifold, h is a representative of a conformal class of Riemannian metrics on I, and D is a rank-2, traceless, symmetric tensor field on I. Based on this, and on the tidal nature of gravitational radiation, a characterisation of gravitational radiation at the conformal boundary is given using the asymptotic properties of the rescaled Bel-Robinson tensor. The asymptotically flat scenario is also reviewed. In this case, the new criterion is shown to be fully equivalent to the classical one based on the news tensor. Also, a new balance law at infinity is presented. (Based on joint work with José M. M. Senovilla)

Let's talk about... the origin of matter!
2023-10-26 17:00 - 19:00

Towards an understanding of the threshold of collapse in full generality
2023-10-31 14:30 - 16:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract: We study dynamical solutions to the Einstein field equations (EFEs) in the strong field regime of gravity, making use of real or complex scalar field matter which may induce gravitational collapse into black holes (BHs). In that regime, the nonlinearities of general relativity (GR) cannot be neglected and, thus, we employ numerical relativity (NR) simulations with the aim to address various fundamental questions. In fact, black hole formation serves as an ideal laboratory in order to test the limits of the theory of general relativity and of our understanding of singularities. On one hand, by constructing a thought experiment, the dynamical formation of astrophysical size black holes can facilitate the study of a potential breakdown of the classical theory that may be associated to the creation of a singularity. On the other hand, critical phenomena in gravitational collapse at the threshold between BH formation or dispersion probe naked singularities, test the validity of the weak cosmic censorship conjecture and, consequently, push the boundaries of our comprehension of GR under extreme spacetime conditions. Our ultimate objective is to comprehend the phenomena at the verge of collapse for diverse matter models, devoid of any symmetry assumptions. Nevertheless, there are several intermediate stages that we must traverse to gradually progress towards our ultimate goal. In this presentation, I will focus on two primary projects involving gravitational collapse that represent a direct outcome of my Ph.D. research over the past two years. The first project explores the formation of astrophysical black holes through real scalar field collapse, while the second project delves into the investigation of the threshold of collapse of a complex scalar field in axisymmetry. In the forthcoming discussion, we will explore the key findings, implications, and future directions emerging from these projects, providing valuable insights into the active field of research of the threshold of gravitational collapse and its consequences for our understanding of singularities in GR.

Mass definition in Newtonian dynamics and Mach's ideas
2023-11-02 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The talk begins with an overview of the conceptual problems of mechanics. Among these problems, force and mass will be considered. Where they came from and how to overcome them are the questions to be addressed in what follows. Regarding the first, the data comes from the study of historical texts, in particular the way physicists articulated experiments and interpretations. We will see that Newton never wrote F=ma but force is interpreted according to Newton's first law of motion. This articulation led to the most common definition of force, which has remained the same for more than two centuries. Regarding the question of how to overcome this problem, an experiment that tests this concept will be presented. If it is possible to test concepts experimentally, we have a method for dealing with conceptual problems

Towards hyperboloidal Numerical Relativity in Generalized Harmonic Gauge
2023-11-03 15:00 - 17:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Abstract: The use of hyperboloidal coordinates in the numerical evolution of hyperbolic Partial Differential Equations promise a clean capture of the radiation signal asymptotically. Although mathematically appealing, a fully satisfactory application of such methods in Numerical Relativity has not been achieved yet. One key difficulty is subtle interplay between the decay of the evolved fields and divergent terms appearing from the use of a compactified domain.In this talk I will present the numerical results of the recently understood asymptotic properties of the Generalized Harmonic Formulation of General Relativity for some choice of gauge and metric functions. In particular, I will discuss 3+1-dimensional evolution of a simplified model with the same asymptotics, as well as full non-linear General Relativity evolutions under the assumption of spherical symmetry. These works are steps towards applying hyperboloidal methods in full Numerical Relativity without symmetry assumptions, which could improve the Gravitational Wave extraction procedure significantly.

Characteristic Critical Collapse with Null Infinity
2023-11-07 14:00 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1/ Online
Resumo:Soluções das equações de Einstein que estão próximas do limite de formação de buracos negros exibem características que relembram fenómenos críticos em mecânica estatística. Neste trabalho, estudamos detalhadamente o colapso crítico de um campo escalar, focando-nos tanto em aspetos locais como globais. Primeiro, mostramos que o campo que colapsa é discretamente auto-semelhante com um período de eco de Δ≈3.4. Notavelmente, quantidades globais como a massa de Bondi ou a função de notícias manifestam o mesmo comportamento discretamente auto-semelhante. Segundo, demonstramos que a massa de buracos negros formados em evoluções perto do limite escala em função da distância ao parâmetro crítico, com um expoente crítico de γ≈0.37. Por último, argumentamos que estes resultados são universais em relação aos dados iniciais. O nosso esquema numérico é baseado numa formulação característica em coordenadas de Bondi compactificadas, com métodos que são globalmente precisos à quarta ordem. A convergência do código é testada e a precisão é melhorada empregando um refinamento analítico da grelha. Finalmente, o colapso de um campo de Yang-Mills é estudado. Este código mostra boa convergência e é fornecida uma análise preliminar do seu colapso crítico.

Probing the Internal Structure and Evolution of Sun-like Stars with Neutrinos and Asteroseismology
2023-11-08 14:30 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1
O desenvolvimento da hélio- e asterossismologia revolucionou a astrofísica moderna revelando o interior previamente inacessível das estrelas, fornecendo restrições novas e independentes ante as quais é possível testar a física estelar, e revelando algumas discrepâncias na reconciliação entre a modelação do interior e da superfície das estrelas.Neste trabalho explora-se a utilização de neutrinos como uma forma de sondar a composição e a estrutura estelar. Num primeiro caso, demonstra-se que o estado-da-arte da astronomia de neutrinos é suficiente para obter informações relativas à abundância de elementos-chave em regiões bem determinadas do Sol, e num segundo, mostra-se a existência de uma ligação entre neutrinos e asterossismologia durante o flash de hélio que poderá ser usada para responder à questão em aberto sobre os processos físicos relacionados com este fenómeno.É demonstrado que uma precisão de 17% na observação do fluxo de neutrinos solares é suficiente para distinguir entre dois modelos de composição, e são calculados os fluxos e os perfis radiais de emissão destes neutrinos.Adicionalmente, também se mostra que a observação direta do flash de hélio é possível para estrelas até cerca de 25 pc da Terra, através da deteção de neutrinos, e que o fluxo específico de neutrinos provenientes do decaimento de 18F podem limitar a abundância de 14N numa zona muito precisa da estrela. Finalmente, demonstra-se o papel determinante dos neutrinos térmicos na estrutura do flash de hélio, revelando uma ligação entre a asterossismologia e a emissão de neutrinos.

Monte Carlo Algorithms for Low-Temperature Plasmas
2023-11-09 10:00 - 12:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
Abstract The main aim of this thesis is to develop and employ Monte Carlo (MC) modelling techniques for the investigation and taming of low-temperature plasmas (LTPs). MC methods simulate physical systems by tracking the temporal of evolution of test particles. The stochastic evolution is performed by generating random numbers sampled from distributions that emulate the underlying physics. In Chapter 2, we present a MC method for solving the complex chemical kinetics of heavy species in LTPs. Additionally, novel variance reduction methods are developed to improve the description of minority species without impacting computation time. In Chapter 3, we present the first version of the LoKI-MC open-source code, which addresses electron kinetics in a gas discharge subjected to a uniform DC electric field. In Chapter 4, we expand the LoKI-MC capabilities to include anisotropic scattering in any collision type. Moreover, we demonstrate that the inclusion of anisotropic scattering in rotational collisions with H2O molecules is fundamental to obtain accurate agreement between modelling and experiment. In Chapter 5, we extend the formulation to configurations involving AC/DC electric and DC magnetic fields. The code is thoroughly verified, and novel benchmark calculations are produced. Additionally, we analyze the impact of magnetic fields in detail, distinguishing between configurations with DC and AC electric fields. Finally, in Chapter 6, we consider the rigorous time-dependent MC solution as the gold standard to evaluate the accuracy of two common assumptions for solving space- and time- dependent electron kinetics: the local-field approximation (LFA) and the local-energy approximation (LEA). The study focuses on homogeneous electron kinetics in nanosecond-pulsed discharges. It is observed that the LEA generally provides more accurate results than the LFA. In general, the methods presented in this thesis allowed for a better understanding of LTPs and an assessment of the accuracy of common approximations used in LTP modelling.

Machine learning with Gaia and large stellar surveys
2023-11-09 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: The Gaia mission as well as large-scale ground-based spectroscopic surveys are collecting complex data for millions (even billions) of stars. The community is therefore using more and more machine-learning methods to cope with the amount of data. In this talk I will present some recent examples of supervised (typically regression) and unsupervised (typically dimensionality reduction and clustering) methods in the context of stellar and Galactic astrophysics. In particular in the field of Galactic open clusters, the combination of Gaia data with machine-learning approaches is revolutionizing a whole field.

Radiation reaction in magnetized black holes
2023-11-13 11:00 - 13:00 | Sala P3 Pavilhão de Matemática, Piso 1/ Online
ResumoNesta tese, estudamos a reação à radiação eletromagnética de partículas carregadas em movimento circular em torno de um buraco negro de Schwarzschild imerso num campo magnético assintoticamente uniforme. Sem considerar radiação, as órbitas circulares neste sistema estão restritas ao plano equatorial e podem ser caracterizadas como estando na configuração positiva ou negativa, dependendo se a força de Lorentz aponta para fora ou para dentro da trajetória, respectivamente. Se incluirmos a radiação, a equação de movimento é a equação de DeWitt-Brehme, que inclui um termo de cauda complexo; há resultados na literatura que afirmam que esse termo pode ser negligenciado.Assim, neste trabalho realizamos uma análise do limite Newtoniano que mostra que a cauda não pode ser negligenciada nesse limite, a menos que toda a radiação seja ignorada, ou a curvatura em si seja negligenciável, dois cenários triviais em que nunca se usaria a equação DeWitt-Brehme.Também estudamos a reação à radiação no regime de campo forte, usando teoria de perturbações de buracos negros. Encontramos expressões para o fluxo de energia no horizonte e no infinito em todos os modos multipolares, para raio orbital e velocidade angular genéricos. Em seguida, calculamos os fluxos de energia propriamente ditos usando métodos analíticos (limitados a movimentos lentos e a modos de baixa frequência) e métodos numéricos; os dois concordam dentro do domínio de validade dos resultados analíticos. Para os valores da frequência do ciclotrão estudados, descobrimos que o fluxo de energia total pode ser calculado com precisão arbitrária (excluindo erros numéricos) usando um número finito de modos; isso parece falhar para órbitas muito próximas ao horizonte de acontecimentos (existem órbitas estáveis nessa região para a configuração positiva). Descobrimos também que, para órbitas na configuração positiva, o aumento do raio orbital leva a que a razão entre o fluxo de energia no horizonte e em infinito de aproxime do valor constante para o modo dipolar, enquanto que tende para infinito para os multipólos de ordem superior. Finalmente, em relação ao termo de cauda na equação de DeWitt-Brehme, o caso de campo forte apenas reforça a afirmação anterior de que ele não pode ser negligenciado no estudo da reação de radiação na solução de Schwarzschild em qualquer cenário não trivial.

Energetics of quantum information processing
2023-11-14 17:00 - 19:00 | Online
Abstract:I present the main projects of my doctoral thesis, whose aim is to understand the energy requirements and limitations of quantum information processing. First, we demonstrate classical logic processing using a trapped-ion quantum computer. A three-bit half-adder is implemented using electronic states of trapped ions. We discuss the energetics by measuring consumed power and theoretical modeling. Second, we investigate energy-fidelity trade-offs when implementing unitaries in driven quantum systems. The fidelity of the operation is quantified by tracing out the degrees of freedom of the driving system, and rigorous mathematical bounds are sought for fidelity guarantees independent of the unitary operation. Finally, the implications of these mathematical bounds are explored in general quantum algorithms using the framework of Quantum Singular Value Transforms (QSVT), including the impact of error correction on error-energy scaling.

A brief history of lasers and plasmas at IST and GoLP
2023-11-15 16:30 - 17:30 | Anfiteatro PA1, Piso -1 - Pavilhão de Matemática, Campus da Alameda
Abstract:In 2023 we celebrate 30 years of the Lasers and Plasmas Group. In this colloquium, I will discuss the first steps in this area at IST, including the origins of plasma physics and laser-plasma interaction studies, the first laser based on the Chirped Pulse Amplification technique (recognized with the 2018 Nobel Prize) from the Iberian Peninsula and the launch of experimental research in laser-plasma and beam-plasma interactions, including harmonic generation and attosecond pulses, and some of the scientific and technological milestones of the last 30 years. I will also present some of the scientific and technological frontiers associated with the most powerful and intense lasers and particle beams that suggest that the next 30 years will also be filled with exciting scientific and technological advances.

Flight data analysis of the BERM radiation monitor aboard the BepiColombo mission
2023-11-16 09:00 - 11:00 | Online (Password: [REDACTED]
ResumoBepicolombo é uma missão conjunta entre a European Space Agency (ESA), e a Japan Aerospace Exploration Agency (JAXA) para explorar Mercúrio. É composta por duas naves, a Mercury Planetary Orbiter (MPO) da ESA e a Mercury Magnetospheric Orbiter (MMO) da JAXA. A missão foi lançada em 2018 e está previsto entrar em orbita de Mercúrio em Dezembro de 2025. O BepiColombo Environment Radiation Monitor (BERM) é o monitor de radiação abordo da Bepicolombo, e tem como objetivo monitorizar a radiação ambiente. O BERM foi desenvolvido pela ESA em cooperação com a empresa Portuguesa EFACEC. Tem a capacidade de detetar elevados fluxos de eletrões com energias desde 100 KeV até 10 MeV, protões desde 1 MeV até 200 MeV e iões pesados desde 1 até 50 MeV/mg/cm2. É composto por um conjunto de 11 detetores de silício, intercalados por tântalo e alumínio. A partir da energia depositada no silício e do padrão de deposição de energia, o BERM separa as partículas em 18 canais: 5 de eletrões, 8 de protões e 5 de iões pesados. O monitor providencia as contagens em cada canal, integradas em intervalos de 30 segundos. Neste trabalho os thresholds do BERM e o cross-talk entre detetores foram analisados com o objetivo de melhorar a caracterização dos canais. Para tal, foram realizados vários testes com uma réplica do BERM e fontes radioativas de 137-Cs e 90-Sr. Os dados da calibração de 2014, com protões, foram reanalisados. Foi criado e implementado um novo modelo do cross-talk nas funções de resposta do BERM. Os resultados foram convoluídos com diferentes modelos de radiação durante o flyby da Terra e comparados com o instrumento Solar Intensity X-Ray and Particle Spectrometer (SIXS), abordo da mesma missão, para validação. O modelo foi bem sucedido em reproduzir os canais de baixas energias de eletrões. A reconstrução dos fluxos em Solar Energetic Particles (SEP) com a bow-tie foi também validada com dados do SIXS.

Transport of particles in nuclear fusion devices
2023-11-16 14:00 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1/ Online (Password: [REDACTED]
O advento da energia de fusão nuclear tem sido altamente antecipado há mais de um século. Neste trabalho, exploramos um conceito promissor para alcançá-la através do confinamento magnético, o stellarator, que quebra a simetria do tokamak, permitindo operação em estado estacionário. Desenvolvimentos recentes no design de dispositivos de fusão por confinamento magnético permitiram a construção de configurações de stellarators excepcionalmente otimizadas. A otimização deste design exige o cálculo iterativo do equilíbrio magnético, tendendo a ser computacionalmente dispendiosa. Esta otimização pode ser acelerada recorrendo a uma aproximação a um equilíbrio magnético, obtida através de uma expansão em torno do eixo magnético. A expansão fornecida tem demonstrado possibilitar a construção de configurações magnéticas com boas propriedades de confinamento, ao mesmo tempo que requer apenas uma fração do tempo de cálculo habitual para gerar equilíbrios magnéticos otimizados. No entanto, pouco se sabe sobre as características gerais das órbitas de partículas rápidas calculadas em tais equilíbrios analíticos, embora simplificados, em comparação com aquelas obtidas em soluções de equilíbrio mais precisas Este trabalho tem como objetivo investigar e demonstrar o potencial da expansão em torno do eixo para fornecer informações precisas sobre as órbitas de partículas e para calcular as frações de perda em diferentes tipos de stellarator. As configurações usadas foram redimensionadas para parâmetros relevantes para a fusão e aproximam a quasisimetria em vários graus. Isso permite-nos entender como os desvios da quasisimetria podem afetar as órbitas das partículas e o seu efeito na estimativa da fração de perda de partículas para a parede. As trajetórias do centro-guia das partículas alfa nascidas da fusão são traçadas usando os códigos \texttt{gyronimo} e \texttt{SIMPLE} sob o enquadramento do código \texttt{NEAT}, mostrando boa concordância numérica Discrepâncias entre equilíbrios precisos e os seus correspondentes na expansão perto do eixo têm efeitos menores em partículas passantes, mas efeitos significativos em partículas presas, especialmente em campos magnéticos quasi-helicamente simétricos As frações de perda de partículas concordam no regime de perdas imediatas, mas divergem posteriormente. As perdas de partículas até 1 ms parecem ser eficazmente modeladas pela expansão junto ao eixo para configurações quasi-axisimétricas Expressões analíticas foram encontradas para estimar larguras de órbita e separatrizes de passagem-aprisionamento de partículas em campos quasisimétricos.

The role of dust reddening in observational cosmology and supernova calibration
2023-11-16 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Modern observational cosmology suffers from worrying unsolved puzzles (i.e., Hubble tension) that can point towards the existence of unaccounted systematic biases in the observations, particularly related to the calibration of standard candles in the local distance ladder, such as Cepheids and supernovae. In the case of type Ia supernovae (SNe Ia), this is further hinted at by the existence of a mass-step, a well-documented discrepancy between the calibrated luminosities of SNe Ia originating in low- and high-mass galaxies, which might indicate that different galaxy populations occur in different rungs of the distance ladder. In this talk, I will discuss some attempts to improve SN Ia calibration, focusing mainly on a more detailed description of dust reddening. Furthermore, I will explore to what extent host galaxy dust data can be leveraged to improve the SN calibration.

Let's talk about... Gravitational Waves!
2023-11-16 17:00 - 19:00

Deployment of a microwave cavity experiment using the Framework for Remote Experiments in Education
2023-11-17 14:30 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1
Os laboratórios controlados remotamente, durante a pandemia COVID-19, tiveram progressos significativos. Sendo o conceito deste tipo de laboratórios relativamente antigo, os mesmos até então tinham tido pouca visibilidade. O mundo académico foi forçado a aumentar a oferta de experiências remotas com maior regularidade e mais fiáveis e consistentes, devido a este estímulo externo. Desde 2000, o Instituto Superior Técnico (IST) fornece várias experiências remotas no seu laboratório remoto e-lab. No entanto, foi necessária a atualização de algum hardware e software, devido à evolução da tecnologia. Assim, para colmatar esta necessidade, foi desenvolvido o ”framework for remote experiments in education” (FREE).Utilizando um computador ou um dispositivo móvel, ligados a uma rede de Internet pública, é possível ter acesso ao laboratório e-lab através de um browser sem necessidade de instalar qualquer software adicional. Os utilizadores podem realizar inúmeras atividades experimentais e os resultados podem ser descarregados a partir da base de dados da aplicação. Com estes dados, realizando a adequada análise dos mesmos podem-se obter os parâmetros físicos. Também são apresentadas as instruções de como integrar uma nova experiência no FREE. A cavidade eletromagnética foi utilizada como prova de conceito. Incluindo ainda exemplos de conjuntos de dados típicos, que se podem obter, e a análise necessária para determinar a densidade do plasma.

Measurements of Higgs boson properties in associated production with top quarks with the ATLAS detector
2023-11-20 15:00 - 17:00 | Online
Medições da produção¸ ao associada de bosões de Higgs com quarks top foram realizadas utilizando 139 fb−1 de dados recolhidos pela experiencia ATLAS no ˆ LHC. Eventos com um ou dois leptões no ˜ estado final e compatíveis com o decaimento H → b ¯b foram selecionados. A secção eficaz de ˜ ttH¯ (H → b ¯b) foi medida de forma diferencial em bins do momento transverso do bosão de Higgs. Foi observado um excesso de eventos relativamente a previsão do fundo com uma significância estatística de 1.0σ (2.7σ esperada). A força do sinal foi medida: 0.35 ± 0.20(stat.) +0.30 −0.28(syst.). As propriedades de cargaparidade (CP) da interação de Yukawa entre o quark top e o bosão de Higgs foram medidas pela primeira vez no canal ttH/tH ¯ (H → b ¯b). Novas variáveis angulares foram utilizadas para distinguir entre cenários de CP. O valor medido do ângulo de mistura de CP ˆ e´ 11◦+52◦ −73◦. Estudos focados no trigger da experiência ATLAS foram realizados. Para a Run 3, triggers dedicados a medidas da produção exclusiva de pares de jatos, combinando informação do detetor central e do AFP, foram implementados. Para o HL-LHC, o desempenho de um trigger de traços foi estudado.

Optimization of materials for Metal-Isolador-Metal resistive devices (Memristors)
2023-11-21 14:00 - 16:00 | Online
Os computadores modernos, baseados na arquitetura determinística de von Neumann, onde a memória e o processamento estão fisicamente separados, não conseguem aprender e adaptar-se a novos ambientes de maneira eficiente e prática. Assim, é necessária uma nova abordagem, e dispositivos capazes de simultaneamente armazenar e processar informação são blocos essenciais de construção. O memristor é uma memória não volátil de dois terminais baseada em estruturas metal-isolador-metal que estabelece uma relação não-linear entre o histórico de corrente e tensão por meio de comutação resistiva. Satisfaz os dois critérios de memória e computação, sendo um candidato promissor para esta nova era de informação.Este trabalho centraliza-se na otimização do processo de microfabricação de dispositivos memristivos baseado em estrutura de Si/Ag, com configuração simples. Dois processos simples, com pequenas alterações, consoante a caracterização dos dispositivos, são implementados onde o contacto à estrutura metal-insulador-metal é definida por litografia ótica e gravura por feixe de iões. Os vários dispositivos foram fabricados com os mesmos materiais, esquiometria e técnicas de deposição, mas com espessuras do elétrodo de topo variáveis, de 2 nm, 5 nm, e 10 nm de Ag. Os filmes finos e dispositivos microfabricados foram caracterizados eletricamente.Neste trabalho, estudámos a comutação resistiva de estruturas metal-isolador-metal. Uma dinâmica do sistema Si/Ag, PT/Si/Ag/TiW, foi fabricada e caracterizada. O comportamento de comutação resistiva bipolar observado é consistente com a formação e rutura de filamentos metálicos de Ag. Si /Ag revelaram histerese bipolar que reivindica o efeito de memória esperado em sistemas memristivos com resistividades baixas e rácio ROFF/RON ~1, respetivamente.

Testing entanglement and Bell inequalities at colliders
2023-11-21 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:In this talk, we explore the experimental prospects to measure the entanglement and violation of Bell inequalities at the LHC. In particular, we will focus on two quantum systems: t-tbar pairs and ZZ produced from Higgs decay.

Confronting Multi-Higgs Models with Experiment: The 3HDM case
2023-11-22 10:00 - 12:00 | Online (Password: [REDACTED]
Nesta tese, estudamos extensões do Modelo Padrão no setor escalar, em particular modelos com N dubletos de Higgs (NHDM).Existe um grande interesse em modelos com três dubletos de Higgs em que fermiões com uma certa carga acoplam a um único e distinto campo de Higgs.Estudamos as diferenças fenomenológicas entre as duas versões comuns deste 3HDM, denominado tipo-Z. Salientamos que as diferenças entre os dois modelos surgem unicamente no potencial escalar.Assim, focamo-nos em observáveis que envolvem apenas acoplamentos entre escalares.Revelou-se difícil descobrir caracteristicas que diferenciem de forma única a variante Z3 do modelo.No entanto, ao estudar a dependência do acoplamento trilinear do Higgs nas massas dos escalares ainda não observados, conseguimos identificar alguns dos indicadores exclusivos da versão Z2xZ2 do 3HDM tipo-Z. Assim, destaca-se a importância de medições de precisão do acoplamento trilinear do Higgs.Neste estudo, e na restante literatura, o 3HDM com simetria Z2xZ2 é considerado no caso de conservação explicita de CP, incluindo apenas parâmetros reais no potencial escalar.De seguida, apresentamos a parametrização física do 3HDM com simetria Z2xZ2 geral, com parâmetros complexos.Demonstramos que o modelo complexo pode, em princípio, permitir um acoplamento h125bb totalmente pseudoescalar, enquanto que h125tt permanece totalmente real.Mostramos também como implementar as restrições teóricas e fenomenológicas de unitariedade, BFB e STU, preparando o trabalho necessário para um estudo do espaço de parâmetros deste modelo num trabalho futuro.

Permanent Magnet Optimization for Nuclear Fusion Reactors
2023-11-22 14:00 - 16:00 | Sala P9 Pavilhão de Matemática, Piso 2
A otimização de equilíbrios magnéticos revolucionou a investigação em stellarators equiparando-os aos tokamaks e trazendo este modelo para o topo da fusão nuclear. No entanto, não é suficiente obter equilíbrios que apresentem resultados ótimos numericamente. É crucial garantir que possam ser reproduzidos com sistemas magnéticos reais. Embora o W7-X tenha sido bem-sucedido em demonstrar experimentalmente a viabilidade de stellarators otimizados, o processo de construção das bobinas revelou-se um grande desafio. Como tal, a procura por formas alternativas de gerar equilíbrios stellarator altamente otimizados é de extrema importância. Neste trabalho, o módulo de otimização SIMSOPT é utilizado para explorar o potencial dos ímanes permanentes como uma ferramenta complementar ou uma solução alternativa às bobinas modulares, tendo duas aplicações em mente: o uso de ímanes permanentes como uma forma de corrigir erros nos campos magnéticos de bobinas modulares e a possibilidade de converter um tokamak num stellarator. O primeiro tenta combinar as vantagens dos ímanes permanentes com o conhecimento já estabelecido em bobinas modulares. Demonstrou-se que os ímanes permanentes são uma ferramenta eficaz para a correção de campos de erro, pelo menos até escalas e campo magnético comparáveis ao W7-X. O segundo representa uma forma de aumentar o número de stellarators em operação, acelerando a pesquisa em stellarators, através da reutilização de componentes de tokamaks desativados. Com o crescente interesse no conceito de stellarators, esta poderia ser uma solução economicamente viável para permitir que mais centros de investigação participem em novos estudos de energia a fusão. Um caso concreto, o ISTTOK, é analisado em detalhe, determinando que opções seriam viáveis na transformação deste tokamak num stellarator.

Materials for Electrochemical Energy Storage in Brazilian Air Force
2023-11-22 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
In the context of the 4th Industrial Revolution, paradigms are changing rapidly. Populations growexponentially and thus more and more needs for security, food, natural resources (especially water),electrical energy, mobility, health, sustainability, among others, are demanded. So, it's necessary todeepen concepts and develop technologies that can accommodate and integrate such aspects.Recently, a lot of progress has been made in relation to energy matrices, mainly due to allegationsrelated to fossil matrices, said to contribute to some degree for the accumulation and transport ofheat outside of previous patterns in the biosphere. This strengthens the discussion about thegeneration, storage and use of energy. In this regard, Brazil has been privileged by its great water,biomass, solar and wind potential. It provides the emergence of multiple business platforms aroundthese resources, with low environmental impact. Furthermore, with renewed strategic guidance inthis field and a very competitive availability of mineral resources with high added value for theseapplications. It includes reserves of graphite, niobium, rare earths and lithium, materials that haveattracted growing interest in this regard. The needs of the electric aircraft market and their energyand power requirements are raised, and compared with storage devices already commercialized or inthe prototype phase. Using electrodes based on niobium, graphene and lithium MXenenanomaterials to the development of battery and supercapacitor packs, the aim is to disrupt theoperation of small mockups in order to have them for future eVTOL and UAV technologies, above thelimits of current devices. The challenge surpasses the automotive one because there are several waysof transferring momentum. So, energy and power consumption can vary greatly depending on them(flat flight, takeoff, landing, angular turns, stall and others), in addition to subsystems containedtherein.

Some Aspects of Symmetry Constrained Multi-Higgs Models
2023-11-22 14:30 - 16:00 | Online (Password: [REDACTED]
Está demonstrado que um modelo com três dubletos de Higgs (3HDM) sob uma simetria A4 exata não é compatível com massas de quarks diferentes de zero e/ou uma matriz CKM não diagonal por blocos. Nesta tese, provamos que um 3HDM com termos A4 softly broken no potencial escalar permite um fit às matrizes de massa dos quarks. Além do mais, o resultado é consistente com mh=125 GeV e as medições de h→WW,ZZ . São também testadas outras simetrias maiores do potencial escalar verificando-se que, embora permitissem o mesmo vev, são inviabilizadas pelo setor de Yukawa. Como resultado secundário, corrigimos uma lista de simetrias do 3HDM presente na literatura. Verificamos, ainda, numericamente que, para cada ponto que obedece a todos os constrangimentos impostos, o mínimo é um mínimo global do potencial.

Towards Brain-Inspired Computing: Memristor-Based Single Layer Neural Networks
2023-11-22 16:00 - 18:00 | Online
This master thesis delves into the realm of neuromorphic computing, a promising paradigm shift poised to overcome the limitations of traditional von Neumann computer architectures in the field of neural network algorithms. The focus is squarely placed on the memristor, a non-volatile memory device that emulates the behavior of synapses in the human brain, offering a scalable and efficient alternative for computing systems. Through rigorous exploration of design, fabrication, characterization, and simulation aspects, this dissertation evaluates the practicality of incorporating memristive devices into neuromorphic computing systems.The research is framed around a multi-faceted approach that includes the innovation of tools and computational frameworks, with a highlight being the development of a pioneering software platform that synergistically integrates the capabilities of LT-Spice and Python. A characterization software, "PyCharMem", has been developed to streamline the characterization process, making it more accessible and scalable. Additionally, a portable probe station was conceived and manufactured, addressing space constraints.A total of 19 distinct memristive devices were subjected to electrical characterization, facilitating the extraction of their critical properties. This exhaustive analysis laid the groundwork for their emulation using SPICE models, navigating the complexities through a genetic optimization algorithm tailored to extract intricate parameters. The research culminates in the execution of single-layer neural network simulations, employing a gradient descent learning algorithm through a reputable SPICE simulator, ensuring a comprehensive and reliable evaluation of sneak paths in memristor crossbars.

Particle Physics anomalies from Dark Matter
2023-11-22 16:00 - 18:00 | Online
O Modelo Padrão é uma das teorias mais bem sucedidas da história. Ainda assim, algumas das suas previsões, como é o caso do momento magnético anómalo do muão, estão em desacordo com as medições experimentais. Há também fenómenos observados que nem são descritos por esta teoria, como é o caso da Matéria Escura. Uma solução habitual é adicionar novas partículas ao Modelo Padrão, cujas propriedades devem ser capazes de explicar as discrepâncias, sem comprometer outras previsões do Modelo Padrão que já se encontram de acordo com as respetivas medições experimentais. Nesta tese, as correções radiativas aos Observáveis de Precisão Electrofracos associados ao bosão Z são estudados e, consequentemente, utilizados para restringir o espaço de parâmetros de tais extensões. Fórmulas explícitas para os desvios dos observáveis no polo do Z em relação à previsão do Modelo Padrão são deduzidas, considerando extensões com números arbitrários de escalares e fermiões. Quando utilizados num modelo promissor seleccionado da literatura, estes observáveis diminuíram eficazmente o espaço de parâmetros permitido, com o novo observável (Reμ) a provocar as maiores restrições. Estes resultados realçam a importância de considerar os observáveis do polo do Z ao trabalhar com extensões do Modelo Padrão que visam explicar a origem da Matéria Escura, enquanto resolvem a discrepância na medição do momento magnético anómalo do muão. Parte deste trabalho foi submetido para publicação [1].

Probing quark hadronization with B mesons at the LHC
2023-11-23 14:00 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1/ Online (Password: [REDACTED]
Na natureza, os quarks não podem existir por si mesmos. Quando são produzidos, como, por exemplo, em colisões de alta energia, os quarks juntam-se a outros quarks para formar hádrons. Esse processo, conhecido como hadronização, é impulsionado pela força forte (QCD) e ainda não é completamente compreendido. Medidas dos mésons B em colisores oferecem sondas únicas do processo de hadronização, pelo qual os quarks individuais formam hádrons de cor neutra.Neste trabalho, os sinais dos mésons $B^{+}$ e $B^{0}_{s}$ são estudados e identificados nas colisões do LHC, utilizando métodos avançados de machine learning.Os mésons B são reconstruídos através dos canais de decaimento $B^{+} \rightarrow J/\psi ~K^{+} \rightarrow \mu^{+}\mu^{-}K^{+}$ e $B^{0}_{s} \rightarrow J/\psi ~\phi \rightarrow \mu^{+}\mu^{-}K^{+}K^{-}$, em dados de colisões pp a uma energia de $\sqrt{s}=5,02$ TeV coletados pelo experimento Compact Muon Solenoid (CMS) no LHC.Esta tese abrange todo o trabalho desenvolvido que engloba uma análise completa. Isso inclui a seleção de eventos, realizada aqui utilizando o pacote XGBoost para a criação de um modelo de boosted decision tree, ajuste de parâmetros das distribuições de massa invariante obtidas e determinação da eficiência do detetor e seleção, na qual aplicamos um método inovador que minimiza a dependência da cinemática de MC e remove a contaminação de background na região de sinal. Também apresentamos comparações de desempenho entre os modelos BDT e redes neurais (NN), juntamente com estudos que visam investigar a região de menor $p_T$, sendo esta mais desafiadora.Com estes ingredientes, medimos a differential production cross section dos mésons B em função das variáveis cinemáticas de sinal (momento transversal e rapidez) e variáveis de ambiente (multiplicidade de partículas carregadas), obtendo resultados consistentes com as previsões teóricas FONLL e resultados anteriores. Calculamos as razões das cross section entre os dois mésons B, investigando as dependências da razão de fração de fragmentação, $f_s/f_u$, nessas variáveis.Os resultados fornecem indícios de um aumento na produção de $B^0_s$ em relação ao $B^+$ em multiplicidades de partículas carregadas elevadas, como seria esperado ao considerar a coalescência de quarks como um mecanismo complementar de hadronização.

Numerical evolution of well-posed field theories with anisotropic scaling
2023-11-23 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Dynamical equations exhibiting an anisotropic scaling between space and time admit a dispersive nature, as they contain higher-order spatial derivatives, but remain second order in time. This is the case of a class of Lorentz-violating theories of gravity, and this feature results inconvenient for performing long-time numerical evolutions with standard explicit schemes. In this talk I will introduce a nobel scheme which is implicit, stable and second-order accurate, for sufficiently large time steps. As a proof of concept, we will apply it for evolving the Lifshitz scalar field on top of a spherically symmetric black hole space-time. Our results indicate that the dispersive terms produce a cascade of modes that accumulate in the region in between the Killing and universal horizons, indicating a possible instability of the latter.

Matter, antimatter and dark matter, and the origin of antinuclei in cosmic rays
2023-11-23 16:00 - 18:00 | Sala V1.06, Pavilhão Civil
Abstract:There may exist B-L violating interactions which can be at the origin of baryon asymmetry both in the visible and dark sectors in the early universe, and they can also induce the mixing phenomena of the neutral ordinary particles with dark particles. I discuss how such interactions can produce antinuclei in the present universe. In fact, AMS-2 experiment has detected eight antihelium candidates and can be explained by this mechanism which also suggests that the heavier antinuclei as anticarbon or antioxygen may also exist in cosmic rays.

Let's talk about... Superconductivity!
2023-11-23 17:00 - 19:00

A model for the analysis of electric signals in the hearth
2023-11-24 09:00 - 11:00 | Sala P3 Pavilhão de Matemática, Piso 1
Estudar a eletrofisiologia do coração é uma tentativa de compreender a essência da sua função. Analisar um eletrocardiograma (ECG) é interpretar a atividade elétrica do coração, permitindo a deteção de anomalias na condução cardíaca. A fibrilação atrial (FA), um tipo particular de arritmia, é causada pela atividade elétrica involuntária na aurícula esquerda do coração. Como consequência, a propagação do sinal cardíaco é prejudicada, afetando a sua velocidade de condução. O objetivo final desta tese é criar um modelo que possa analisar o ECG, classificar o seu estado e estimar a velocidade média de condução do sinal atrial. Para atingir este objetivo, foram selecionados pacientes com FA submetidos a ablação cardíaca (um tratamento para a FA) no Departamento de Cardiologia do Hospital de Santa Marta, e os dados de ECG de 12 derivações, registados antes e após o procedimento de ablação foram analisados. Em seguida, comparámos os dados do ECG de pacientes e de indivíduos saudáveis e estimámos as respetivas velocidades de condução. A abordagem resultou em modelos de Machine Learning e de Deep Learning que podem distinguir com precisão entre os dados de ECG de pacientes antes e depois da ablação e dados de indivíduos saudáveis. Através de várias abordagens testadas, uma rede neural artificial com duas camadas ocultas simples superou todos os seus concorrentes, distinguindo os conjuntos de dados com uma precisão máxima de $96,90\%$. O seu desempenho foi seguido pelo algoritmo Random Forest, que se revelou o melhor ajuste entre os modelos de Machine Learning implementados. Um algoritmo de Decision Tree foi optimizado, proporcionando os melhores resultados para a estimativa das velocidades. O modelo foi capaz de estimar uma velocidade média de condução do sinal atrial de 60,86 ± 10,79 cm/s para os indivíduos saudáveis e um valor de 41,62 ± 20,36 cm/s para os pacientes antes da ablação. Os resultados da Decision Tree, reforçados pela correlação observada da característica extraída "Positive Slope V1", que representa a inclinação da variação positiva da onda P, encontrada no canal V1 do ECG de 12 derivações, dão fortes indícios de que esta característica reflete a velocidade de condução do sinal atrial.

Many-body quantum kinetics: the role of light-matter interactions
2023-11-24 09:30 - 11:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: Classical kinetic theory is a very successful tool to understand the dynamics of many-body systems that display low degeneracy and low-to-moderate correlation degree. In particular, the behavior of high-temperature plasmas is very well captured using classical kinetic theory, for which the latter assumptions are particularly valid. However, as the microscopic details of the interactions become more and more important, as well as quantum degeneracy and/or correlations start to play a role, the resulting equations loose their validity, and ab initio quantum approaches are required. In this talk, I will discuss recent results of the application of quantum kinetic theory to study the interactions between matter and radiation in terms of Wigner functions. I will start by introducing the main features of kinetic theories (both classical and quantum), and analyze their validity. The case of a quantum plasma will be examined in detail. Then, as an application, I will discuss photon condensation in plasmas and photon turbulence in cold atoms.

Morphogenesis of Drosophila early development: calibration of the distribution of pair-rule proteins
2023-11-24 11:00 - 13:00 | Sala C10, Pavilhão Central, Piso 1, Campus Alameda
A Drosophila melanogaster é essencial para compreender a macroevolução ao nível molecular. O objectivo desta tese é a construção de um modelo matemático que descreva a expressão de dois genes pair-rule, eve e ftz, fundamentais na formação de segmentos na fase embriónica da Drosophila. Começamos por derivar um sistema base que define os mecanismos necessários no controlo da transcrição de um gene: produção livre de uma proteína, ativação e repressão. Considerando um argumento puramente termodinâmico, a lei de massa-acção, propomos uma definição da região segmentada pelas proteínas terminais Tll e Hkb e uma regulação individual de riscas do padrão do Eve com cinco promotores essenciais. O modelo de cada promotor é testado contra os dados experimentais, e optimizado com recurso a um algoritmo de Monte Carlo. Considerando uma transcrição heterogénea do mRNA ao longo do embrião, calibramos espacialmente a taxa de produção de Eve. A mesma estratégia cinética foi utilizada na identificação de três promotores, e respectivos reguladores, do ftz. Alcançamos com sucesso a calibração dos padrões do Eve e Ftz, revelando como as duas proteínas se podem desenvolver de forma totalmente independente, com uma “leitura” diferenciada dos mesmos conjuntos de fatores gap repressivos. Exploramos ainda um conceito alternativo de repressão direta entre o Eve e o Ftz, mostrando como este é suficiente para explicar a formação do padrão perfeitamente complementar do Ftz. Por fim, provamos que a regulação dos genes segment-polarity é bem descrita por um modelo cinético de massa-acção.

Higgs Production at the LHC with Colored Scalars from Dark Sector Models
2023-11-27 08:00 - 10:00 | Online (Password: [REDACTED]
Motivados pelas discrepâncias em observáveis relacionados com o decaimento do mesão-B entre outros resultados conhecidos como Lepton Flavour Universality, foram propostas uma classe de modelos que resolvem o problema pela adição de novos campos um dos quais é um candidato a matéria escura. Os novos campos geram diagramas com partículas de matéria escura ao nível quântico que resolvem a discrepância entre o valor medido do g-2 do muão e o cálculo teórico do Modelo Padrão (MP). Esta solução é acompanhada por um número de escalares com cor que interagem com o bosão de Higgs do MP. Neste projeto, calculamos as contribuições de primeira ordem para a secção eficaz de um Higgs e dois Higgs padrão, no Large Hadron Collider (LHC) com uma energia do centro de massa de 14 TeV. Os cálculos analíticos são implementando em dois programas relacionados com a produção de Higgs, HIGLU e HPAIR. Tomando em conta as buscas por escalares com cor no LHC apenas consideramos massas pesadas. Em particular, exploramos massas no intervalo entre 0.8 TeV e 5.0 TeV. Os resultados são usados, em conjunto com os limites experimentais atuais mais relevantes, para restringir o espaço de parâmetros das massas dos escalares e dos seus acoplamentos ao bosão de Higgs. Consideramos também os limites projetados em futuras experiências, tais como o projecto do LHC de alta-luminosidade (HL-LHC).

Ga2O3 membrane nanodevices
2023-11-27 10:00 - 12:00 | QA1.2, Torre Sul, Piso 1, Alameda
Neste trabalho, tubos de β-Ga2O3, exfoliados a partir de um cristal em orientação (100) com uma nova técnica de exfoliação assistida por feixe de iões, foram usados para criar dispositivos para testar como fotodetetores e transístores de efeito de campo (FET). Primeiramente, o processo de fabricação dos dispositivos foi otimizado. Este inclui a transferência de tubos para um novo substrato, um passo de recozimento no qual estes se desenrolam em membranas, a colocação de máscaras de sombra e a deposição de contactos elétricos. Os contactos seriam também otimizados e, para contactos de Ti/Au, foi encontrada uma temperatura ótima para a obtenção de contactos óhmicos por volta dos 500 °C, para recozimentos em atmosfera de N2, em concordância com a literatura. Os dispositivos testados como fotodetetores provaram não ser insensíveis ao espetro solar (solar blind), mas mostraram respostas distintas nos casos em que os contactos são iluminados diretamente ou em que apenas a membrana recebe luz direta. Foram efetuadas medidas transientes, com tempos de resposta da ordem de 1 s medidos para a luz de uma lâmpada de deutério. O dispositivo testado como FET encontrava-se em modo de depleção, com uma tensão de limiar de -23,2 V e um rácio on/off de 8600 para uma tensão de -10 V entre dreno e fonte. Como interruptor, o FET mostrou um tempo de resposta substancialmente mais baixo do que o tempo entre medidas, sendo este cerca de 1 s, bem como uma excelente estabilidade após 500 repetições.

Energy Communities Managed by Municipalities: Case Study in Castelo Branco
2023-11-27 14:00 - 16:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
ResumoOs previsíveis efeitos drásticos das alterações climáticas no planeta impelem à mobilização de esforços e criação de compromissos que possam levar à concretização de uma célere e eficaz transição energética. Esta estará, inegavelmente, ligada a alterações nos padrões de consumo e geração de eletricidade e, invariavelmente, alicerçada na aposta em fontes de energia renováveis. Neste sentido, as comunidades de energia assumem-se como uma ferramenta útil ao serviço do cumprimento de metas ambientais, enquanto permitem a gestão autónoma e descentralizada de energia, com potenciais benefícios económicos para os seus participantes.Neste trabalho, é avaliada a possibilidade de criação de uma comunidade de energia composta por edifícios públicos e residenciais, que poderá beneficiar de intervenção do Município. São estudados os perfis de consumos elétricos, as condições de geração de energia através de painéis fotovoltaicos em diferentes cenários e a utilização de sistemas de armazenamento. Por fim, são criados vários cenários de mercados locais de energia, testando modelos de agregação e transações peer-to-peer.Os resultados sugerem que modelos de transação peer-to-peer apresentam benefícios para os participantes, embora a presença de um agregador não seja universalmente vantajosa. Deste modo, um conjunto de participantes poderá operar gerido por um agregador, eventualmente designado pelo Município, enquanto os restantes conservam maior autonomia. Além disso, a comunidade de energia proposta promove consideráveis níveis de auto-consumo e auto-suficiência, ao mesmo tempo que presta um contributo relevante para a redução de emissões de gases com efeito de estufa.

Reinforcement Learning for Battery Operation: Energy Arbitrage Considering Battery Degradation
2023-11-27 16:00 - 18:00 | Online
Os sistemas de armazenamento de energia (BESS) proporcionam aos seus proprietários maior controlo sobre o uso de energia. Realizando arbitragem de energia (EA), os proprietários conseguem reduzir as suas despesas energéticas. Contudo, a maioria carece do conhecimento necessário para optimizar estes sistemas para EA. Neste tipo de ambientes de sistema de energia dinâmicos, a aprendizagem por reforço (RL) destaca-se como uma poderosa ferramenta de tomada de decisão, capaz de maximizar os lucros alcançáveis por EA. Todavia, o desempenho de uma bateria é inconstante, porque a sua capacidade diminui progressivamente. É fundamental tomar em conta esta degradação da bateria para obter resultados fiavéis, pois pode prejudicar potenciais lucros de EA, talvez mais ainda se for desconsiderada. Este trabalho utiliza RL para encontrar a forma ideal de operar uma bateria que fornece serviços de EA residencial, considerando a degradação da bateria prevista por um modelo de aprendizagem semi-supervisionada. Analisam-se três cenários: um onde o algoritmo é treinado numa bateria com capacidade máxima constante irrealista, um que considera a capacidade real ao longo da vida da bateria e calcula o verdadeiro resultado das decisões tomadas no primeiro cenário, e um onde o algoritmo é treinado numa bateria com capacidade real decrescente. Os resultados mostram que, se a degradação for desconsiderada durante a operação da bateria, os custos de degradação reduzem potenciais lucros em 13%. Se considerada, esta percentagem cai para 4%. Ter em conta a degradação pode também aumentar a vida da bateria em 20%, adiando a sua substituição e investimentos associados.

Heavy Neutrino-Antineutrino Oscillations at the FCC-ee
2023-11-27 17:00 - 19:00 | Online (Password: [REDACTED]
Desde a década de 70, o Modelo Padrão (SM) da física de partículas assegurou uma descrição precisa da interação eletrofraca e da força nuclear forte. No entanto, a deteção de oscilações de neutrinos leves entra em conflito com a falta de termos de massa de neutrinos nesta teoria. A extensão da mesma a neutrinos estéreis pode corrigir o problema através do mecanismo seesaw tipo I. Os modelos seesaw testáveis em colisores são geralmente protegidos por uma simetria semelhante ao número leptónico, fazendo com que leptões neutros pesados (HNLs) apareçam como pares neutrino-antineutrino pseudo-Dirac.Tal como os mesões neutros, estes podem oscilar entre estados de partícula-antipartícula, provocando a violação do número leptónico (LNV). Recentemente, a análise de Monte Carlo demonstrou que o Grande Colisor de Hadrões (LHC) é capaz de investigar este fenómeno.Colisores de leptões, como o Futuro Colisor Circular de e+e- (FCC-ee), serão cruciais na procura de neutrinos long-lived. Este trabalho discute a sua capacidade no estudo de LNV através de oscilações de neutrinos-antineutrinos pesados (NNOs). Para tal, demonstrou-se que distribuições de observáveis, como a assimetria forward-backward dos HNLs e o momento dos respetivos produtos de decaimento, desenvolvem dependência oscilatória no tempo de vida dos HNL.Estes sinais, possivelmente resolúveis para HNLs long-lived, contêm informação sobre a geração de massa de neutrinos e permitem a descoberta de LNV. Mesmo quando não são diretamente observáveis, estas propriedades podem ser investigadas através das distribuições integradas no tempo. Os resultados mostram que NNOs devem-se incluir nas simulações de HNLs no FCC-ee.

Resonant interaction of fusion alphas and shear-acoustic Alfvén eigenmodes in burning plasmas
2023-11-28 14:00 - 16:00 | Anfiteatro AM, Pavilhão Mecânica II, Piso 1, Alameda

NMR quantum information processing on liquid chloroform and continuous-time quantum walks on squares
2023-11-28 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract: Recentemente, a área de processamento de informação quântica (QIP) tem-se vindo a tornar progressivamente mais popular à medida que mais aplicações com relevância prática para a sociedade são desenvolvidas. Isto resulta num aumento da procura por profissionais com conhecimento de QIP, que as faculdades têm dificuldade a acompanhar, uma vez que experiências de QIP requerem instrumentação altamente especializada e complexa. Isto faz com que RMN seja uma plataforma atrativa para introduzir estudantes a QIP experimental, pois a maioria das universidades disponibiliza acesso a espetrómetros de RMN. Este trabalho consiste numa introdução experimental a QIP em RMN líquido.Duas amostras de clorofórmio líquido são usadas, uma reforçada com 13C e outra com 12C, que correspondem a sistemas de 2-qubits e 1-qubit, respetivamente. Começa-se por apresentar a teoria de QIP de 1 e 2-Qubits em RMN líquido, descrevendo a preparação de estados pseudo-puros, a implementação de portas lógicas quânticas de 1 e 2 qubits e o mecanismo de leitura. Quanto à parte experimental, implementa-se diversas portas de 1-qubit no sistema de 1-qubit. No sistema de 2-qubits, mede-se os tempos de relaxação T1, T2 e T2* e faz-se experiências onde se implementa a porta CNOT, e unitários de geração de entrelaçamento quântico e de transferência quântica de estados, obtidos a partir de uma CTQW em quadrados de lados sinalizados. As experiências de implementação de portas de 1-qubit e CNOT indicam que temos experimentalmente universalidade de portas de 2-qubits. Um pacote de Mathematica foi desenvolvido com funcionalidades que apoiam o trabalho teórico e experimental.

Linearization of High Sensitivity Out of Plane Magnetic Sensors
2023-11-29 09:00 - 11:00 | Sala P3 Pavilhão de Matemática, Piso 1
No panorama da revolução da "Internet das Coisas" (IoT), a necessidade de sensores compactos, robustos e energeticamente eficientes torna-se cada vez mais crítica. Entre os sensores magnéticos, os sensores TMR perpendiculares (OOP) destacam-se pelo seu potencial de oferecer uma relação sinal-ruído significativamente melhor, excelente escalabilidade e uma robusta estabilidade térmica. Além disso, à medida que a procura para melhorar a deteção em várias aplicações persiste, a versatilidade e adaptabilidade dos sensores OOP TMR na afinação da sua linearidade e sensibilidade anunciam um futuro promissor deste tipo de sensores. Para compreender e otimizar sensores magnéticos OOP para aplicações específicas, um estudo abrangente foi conduzido, dividido em simulações e fabricações práticas. Utilizando simulações micromagnéticas de diferenças finitas, o comportamento magnético destes sensores foi extensivamente estudado. Isto ajudou a compreender a interação RKKY, o acoplamento de troca interfacial e as anisotropias volumétricas, além de fornecer uma compreensão detalhada do comportamento dependente da temperatura e dos parâmetros de design para requisitos específicos.No INESC MN, sensores OOP reais foram fabricados e caracterizados utilizando um novo dispositivo construído. Este dispositivo permite leituras de sensores simultâneas, permitindo assim a recolha em massa de dados para análises estatísticas mais confiáveis. Estas caracterizações concluíram que a melhor temperatura de annealing se situa perto dos 300ºC, onde alguns sensores alcançaram um efeito magnetoresistivo (MR) de quase 60\%. Este estudo também revelou a dependência de parâmetros importantes, como a linearidade e coercividade destes sensores em função da espessura e geometria do CoFeB.

Developing partial-volume multi-beam FLASH with Proton Beams
2023-11-29 13:00 - 15:00 | Online
Abstract:The work for this doctoral research has been mainly developed at the German Cancer Research Center (DKFZ), Heidelberg, Germany, and at the Centro de Protonterapia Quirón salud (CPT), Madrid, Spain, with support from the Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Lisbon, Portugal.The main purpose of this work is to investigate how to implement multi-beam FLASH technique in proton radiotherapy, going from simulations using the treatment planning tool-kit MATRAD, to a clinical application with Raystation (RaySearch Laboratories, Stockholm, Sweden), a commercial treatment planning system (TPS), and delivery in with a ProteusOne protontherapy system (Ion Beam Applications, Leuven, Belgium).

Machine learning for optimizing plasma resource utilization on Mars
2023-11-29 14:00 - 16:00 | Anfiteatro GA2, Pavilhão Central, 0, Alameda
Abstract: On Mars, the atmosphere plays a pivotal role in the In-Situ Resource Utilization (ISRU) perspective, mainly due to the abundant atmospheric CO2. Plasma technologies, especially the application of low-temperature plasmas (LTPs), have been proposed to decompose the existing CO2, facilitating the recovery of O2 and CO to support life, fuel, and agriculture. However, much remains to be done regarding accurate plasma modeling, which relies on the availability of precise reaction rate coefficients. Determining these constants is a non-trivial task, primarily addressed by scientists with extensive experience in the field.In this thesis, we investigate the use of machine learning techniques to predict these parameters. This is done with an automated and systematic approach, based on the heavy-species densities of the gas's final state. The training data is generated using the Lisbon Kinetics simulation tool (LoKI).Both Support Vector Regression (SVR) and Artificial Neural Network (ANN) models were trained using an oxygen (O2) plasma kinetic scheme, encompassing 11 species and 53 heavy-species reaction processes. When evaluated on a test dataset, the top performing SVR and ANN models achieved mean relative error values of 0.10% and 0.22%, respectively. Although both models exhibited significant accuracy, the SVR model emerged as superior, offering both simplicity and heightened performance for our specific low-dimensional dataset. These two machine learning approaches serve as a successful preliminary step towards more comprehensive models to automate the prediction of reaction rate coefficients.

Premises of signal beyond the Standard Model ? Run2 results from the ML based search of supersymmetric top
2023-11-29 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:The LHC machine has delivered an unprecedented number of proton proton collisions at 13 TeV, so far our best window to look for phenomena beyond the Standard Model (SM) of particle physics. The search for the lightest supersymmetric top (stop) has been one of the most motivated search directions during the Run2 of the LHC.In this talk, I will present the latest results of the CMS collaboration on the search for the stop decaying in four bodies. This decay mode, where the observable particles can be extremely soft, is very challenging, while motivated by measurements of the cold dark matter. The search is harnessed on a Machine Learning approach, which is adapted to different signal masses. I will scrutinize the observation of a 2.5 sigma excess of data versus the predicted SM background, and briefly cover perspectives for this search.

Dark matter searches at the LHC
2023-11-29 15:00 - 17:00 | Online
The lack of suitable dark matter (DM) particle candidates in the Standard Model of particle physics (SM) hints at the need for a dark sector to be added to the model. One simplified dark matter model that does this type of extension is the DMsimp model. In this work, we present a phenomenological study where we successfully perform the reconstruction of the top-anti-top system in the presence of a DM mediator, Y0, described by the DMsimp model, that couples to both the SM particles and the dark sector. Events involving Y0 production with a top-anti-top pair were generated for the Large Hadron Collider (LHC) using MadGraph5_aMC@NLO for four different mediator masses: 0 GeV, 1 GeV, 10 GeV and 125 GeV. The reconstruction of the top-anti-top system is done with a kinematic fit for the dileptonic final states, without reconstructing the mediator. Lastly, confidence level exclusion limits are set on the mediator couplings with the top quarks for all generated mediator masses using CP angular observables to probe the CP-nature of the couplings.

Quantum Jet Clustering Algorithms
2023-11-29 16:00 - 18:00 | Online
O Large Hadron Collider (LHC), na Organização Europeia para a Investigação Nuclear (CERN), acelera principalmente feixes de protões uns contra os outros com o objetivo de testar modelos e teorias na Física Fundamental. Espera-se que comece a operar no regime de Alta Luminosidade (HL-LHC) no início de 2029. O HL-LHC irá permitir um aumento substancial do número de colisões de interesse, contribuindo para o estudo de um tipo ainda mais amplo de eventos. No entanto, a sobreposição de eventos indesejados, fenómeno chamado de Pileup, e muitos outros desafios tornarão a tarefa de reconstrução de eventos, especificamente o agrupamento de partículas em jatos (jet clustering), muito mais árdua.Desta forma, é urgente melhorar os algoritmos atuais utilizados para a reconstrução de eventos e agrupamento de jatos ou desenvolver versões mais rápidas e eficientes. O foco desta Tese reside na exploração versões mais robustas e rápidas do K-Means, com ênfase numa implementação alternativa de uma sub-rotina quântica para o cálculo de distâncias euclidianas com base no procedimento de Swap Test. Propomos também uma aplicação mais flexível do K-Means, que descarta jatos com baixo momento transversal, de forma a que o número de jatos encontrados possa ser 0 e não 2, como o algoritmo regular do K-Means exigiria. São ainda abordadas algumas limitações do K-Means e exploramos a aplicabilidade do algoritmo quântico de Affinity Propagation para o problema do agrupamento de jatos. Finalmente, para lidar com o Pileup, fornecemos, até onde sabemos, a primeira incorporação de um algoritmo de mitigação de Pileup com o K-Means.O desempenho dos nossos algoritmos é testado em comparação com referências clássicas, em particular algoritmos de recomposição sequencial, como o kt e o Anti-kt. Com a rotina quântica proposta e os cortes aplicados, os nossos algoritmos alcançaram uma melhor identificação de clusters e altas eficiências. Mostramos que a nossa implementação do K-Means é mais robusta e rápida, uma vez que a sub-rotina quântica proposta requer muito menos consultas do que o procedimento comum e calcula uma estimativa mais precisa da distância euclidiana.

Quantum Field Theory and Relativistic Stars
2023-11-30 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: What are the essential aspects of quantum theory needed in order to understand compact relativistic objects? Relying solely on universal properties of QFTs at high energies, we show that as a star contracts towards its Buchdahl (rather than its Schwarzschild) radius, the effects of the trace anomaly become macroscopic at densities much below the Planck scale. The consequences of this may be observable, as we illustrate with minimally coupled scalar waves.

Stability of spin-liquid phases against environment-induced dissipation
2023-11-30 16:00 - 18:00 | Online
É de grande interesse compreender o impacto do acoplamento de fases líquidas quânticas a diferentes ambientes. Neste trabalho, estudamos a estabilidade da fase líquida de Luttinger relativamente a dissipação induzida pelo ambiente. Para concretizar este objetivo, desenvolvemos um método de Monte Carlo quântico no formalismo de integral de caminho em tempo contínuo com updates de Worm. As recentemente desenvolvidas wormhole updates, que permitem a simulação eficiente de sistemas quânticos abertos, foram adaptadas ao nosso método. Mostramos a validade da nossa técnica testando-a em relação aos resultados do modelo de spin-bosão provenientes de simulações de Monte Carlo quântico anteriores. Também comparamos os nossos resultados para o modelo de Bose-Hubbard dissipativo de um e dois sítios relativamente a diagonalização exata. Estudamos, então, o modelo unidimensional de Bose-Hubbard num contexto não dissipativo e dissipativo. No caso dissipativo, o sistema é acoplado a um banho de osciladores de tal forma que o sistema e o banho podem trocar energia e partículas, mas o número total de bosões é conservado. Descobrimos que a fase líquida de Luttinger é instável para qualquer acoplamento infinitesimal a um banho ôhmico, o que induz, no seu lugar, uma fase superfluida ordenada onde a simetria U(1) é quebrada espontaneamente. Estes resultados são também apoiados por um argumento de contagem de potências. A fase de Mott permanece uma fase distinta para pequeno acoplamento ao banho, mas adquire uma compressibilidade divergente no limite termodinâmico. Para um acoplamento ao banho mais forte, observamos uma transição de fase quântica desta fase para a fase superfluída ordenada.

Novel thin-film silicon photodetectors for biosensing
2023-12-04 10:00 - 12:00 | Online
Biossensores são dispositivos capazes de identificar ocorrências biológicas numa amostra, convertendo um sinal resultante num sinal elétrico que pode ser quantificado. Em particular, os fotodetetores de silício amorfo hidrogenado (a-Si:H) são pertinentes para integração numa plataforma lab-on-a-chip projetada para deteção optoelectrónica. Este trabalho teve como foco o desenvolvimento de um novo fotodetector de a-Si:H com base numa junção p-i-n lateral, para aplicações posteriores de biodeteção. Esta estrutura contrasta com o fotodíodo padrão, que é composto por uma junção p-i-n perpendicular. A microfabricação do dispositivo foi realizada em ambiente de sala limpa e foi alcançado um processo otimizado após duas gerações de dispositivos. O novo dispositivo foi caracterizado quanto às suas principais características: fotocorrente e corrente negra-tensão, com menção dos mecanismos de condução no escuro; eficiência quântica externa em função do comprimento de onda incidente; e fotocorrente em funcão do fluxo de fotões. Foi observada retificação nestes dispositivos, apesar de tenderem para a atuação como um fotodíodo sob polarização reversa e como um detetor fotocondutor sob polarização direta.

Monte Carlo simulations of ion channelling spectra to study implantation damage in GaN with different surface orientations
2023-12-04 15:00 - 17:00 | Online
Implantação iónica permite dopagem de GaN em concentrações elevadas para fabrico de dispositivos com base em GaN pre-depositado, mas cria defeitos. Espectrometria de Retrodispersão de Rutherford com Canalização (RBS/C) permite o estudo destes defeitos, mas isto é dificultado pela diversidade destes.Simulações Monte Carlo (McChasy) e Aproximação de Dois Feixes (TBA) foram comparadas em análise de espectros de RBS/C de c-, m- e a-GaN implantado com Ar. Os perfis obtidos foram comparados com imagens de Microscopia eletrónica de Transmissão (TEM) e contextualizados com o modelo de Hecking.RBS/C mostra perfis de Átomos Aleatoriamente Dispersos (RDA) relativamente semelhantes para c- e m-GaN, com a-GaN apresentanto muito menos danos. Estas curvas mostram crescimento até saturar para fluências de Ar entre 1015 e 1016 at/cm2, seguido de crescimento de defeitos atribuído a amorfização. Os modelos obtiveram perfis semelhantes, com McChasy apresentando valores consistentemente inferiores a baixa (< 250 nm) profundidade e superiores caso contrário. Defeitos extensos foram modelados como loops de deslocações seguindo uma distribuição de vagas, com comportamento semelhante a RDA até aproximadamente 1016 at/cm2, divergindo de saturação para fluências superiores.Comparando estes resultados com imagens de TEM, os perfis de RDA com fluências de 8x1015 at/cm2 eram semelhantes entre modelos mas ambos subestimam ligeiramente a profundidade dos danos. Defeitos extensos consistem maioritariamente de falhas de empilhamento (tanto basais como prismáticas) para c- e m-GaN, e loops de deslocações para a-GaN. Para fluências de 4x1016 at/cm2, os perfis de danos não coincidiam com experiência devido à presença de bolhas de Ar e amorfização.

Amazônia e a Atual Política Ambiental Brasileira: IST Distinguished Lecture (Joint organization with Plataforma de Ciências e Engenharia do Ambiente do IST)
2023-12-04 15:00 - 16:00 | Anfiteatro Abreu Faro - Complexo Interdisciplinar
ResumoDesde o final da década de 1980, o Brasil teve grande protagonismo na questão de mudanças climáticas e combate à degradação ambiental. Um exemplo paradigmático dessa política de estado é o projeto PRODES, do Instituto Nacional de Pesquisas Espaciais, que faz o monitoramento por satélite do desmatamento por corte raso na Amazônia Legal, fornecendo, desde 1988, as correspondentes taxas anuais. Seus dados são internacionalmente considerados entre as melhores series temporais de monitoramento de desmatamento em florestas tropicais. Infelizmente, durante o período de 2019 a 2022, o Governo Federal adoptou uma política negacionista com relação ao aquecimento global e à preservação ambiental, estimulando o desmatamento da Amazônia, que cresceu de 5.078 Km2, em 2018, a 10.573 km2, em 2022. Esse aumento do desmatamento fez com que boa parte da Floresta Amazônica passasse de absorvedor para emissor de gás carbônico para a atmosfera. Essa política predatória foi felizmente revertida com a posse do novo Governo em janeiro de 2023. Entre janeiro e agosto deste ano, houve uma redução de cerca de 48% do desmatamento na Amazônia Legal, em comparação com o mesmo período do ano passado. Neste colóquio farei uma breve descrição das diferentes ações do atual Governo com relação ao desenvolvimento sustentável e combate à degradação ambiental no Brasil, incluindo estímulo a projetos científicos dirigidos a esses tópicos.

Design and commissioning of the magnetic diagnostics system for COMPASS-U
2023-12-05 09:00 - 11:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
O sistema de diagnóstico magnético fornece dados fundamentais para a operação e exploração científica de dispositivos de fusão nuclear por confinamento magnético. Embora esteja em constante aperfeiçoamento desde os primeiros dispositivos, a construção de novos reatores representa uma oportunidade para avanços em diagnósticos magnéticos, adaptados aos desafios e oportunidades específicos. O tokamak COMPASS-U, desenvolvido em Praga, na República Checa, terá um conjunto único de parâmetros, dos quais se destaca o campo magnético toroidal de 5 T e a parede interna metálica aquecida a altas temperaturas. Graças a uma ampla coleção de sistemas de diagnóstico, este dispositivo estará numa posição de suportar a operação do ITER e abordar problemas relevantes tanto para o DEMO como futuras centrais elétricas. Nesta tese, os desafios relativos ao desenvolvimento de um sistema de diagnóstico magnético para uma máquina tão única são discutidos e é exposto o projeto e desenvolvimento dos principais subsistemas: desde os sensores ao cabeamento e eletrónica. São desenvolvidos métodos para calibração e medição precisas de sensores magnéticos; estuda-se a mitigação da influência de estruturas metálicas em sensores; são tiradas conclusões sobre a escolha de cabos de transmissão de dados para longas distâncias; é qualificada a implementação de métodos de integração numérica em tempo-real e novo hardware é desenvolvido. Embora estas etapas de desenvolvimento tenham como objetivo último a adequação à operação e ao programa científico do COMPASS-U, as abordagens sistemáticas descritas e levadas a cabo podem ser aplicadas a dispositivos futuros.

A digital twin for the energy system of Instituto Superior Técnico (Alameda Campus)
2023-12-05 09:00 - 11:00 | Online
Digital twins were born 20 years ago but have only now matured enough, being strongly supported by the advancements of Industry 4.0. By integrating sensors, internet of things, cloud computing, and machine learning, digital twins are endowed with strong capabilities of monitoring, prediction, and diagnosis. This in turn assures a more efficient and optimized management of power grids, promoting, amongst others services, demand-response strategies, renewable energy sources and prosumers integration in the grid, fault prediction, and maintenance routines scheduling. Digital twins bring integration and intelligence to operations management, highly supporting decision making. The path paved by this technology is just beginning. In the following years, digital twins will further penetrate into different industries and will soon become an essential tool in every control room.The objective of this work will be to implement a digital twin of the energy consumption of Instituto Superior Técnico. To achieve this, robust forecasting models will be created, supported by real-time data provided by the smart meters already installed on campus. A framework will be designed to independently and automatically update the models as new data is collected, ensuring they remain faithful to the real process. The collected data and the resulting predictions will be integrated into a novel visualization tool permeated with important visual elements, whose collective added value will ultimately support a better management of the electricity service in Instituto Superior Técnico.

Accelerating track reconstruction using GPUs at ATLAS
2023-12-05 11:00 - 13:00 | Online
Nas últimas décadas, os aceleradores de partículas foram cruciais para grande parte avanços experimentais no ramo da ciência que estuda os constituintes fundamentais do universo, a física de partículas. O atual entendimento teórico, o Modelo Padrão, tem lacunas cuja resolução requer a utilização de conjuntos de dados cada vez maiores, permitindo a observação de processos raros ainda por estudar. Por este motivo, o LHC beneficiará de um projeto de modernização que visa aumentar significativamente a taxa de colisões, o LHC de Alta Luminosidade (HL-LHC). Nas várias experiências, tal como ATLAS, é imperativo melhorar as capacidades computacionais para lidar com o elevado fluxo de dados. Uma alternativa emergente é a utilização de GPUs como plataformas auxiliares para as quais parte da carga de trabalho é delegada. Estes dispositivos potenciam a velocidade das aplicações através de processamento paralelo massivo.O trabalho apresentado nesta tese procura desenvolver e melhorar algoritmos de reconstrução de trajectórias de partículas recorrendo a GPUs. A reconstrução é um processo crucial que consiste em identificar o percurso de cada partícula ao atravessar o detetor e interagir com material sensível, permitindo o estudo das suas características. Em ATLAS, é a tarefa que exige maior tempo computacional. A cadeia de reconstrução do pacote ACTS foi parcialmente implementada com sucesso utilizando CUDA e SYCL: desde dados que provêm diretamente do detetor, correspondentes a células ativas, até à produção de estimativas iniciais de trajectos de partículas.O estudo do desempenho apresentado nesta tese revelou resultados promissores: a capacidade de processamento para eventos simulados em condições semelhantes às que se esperam para o HL-LHC foi aumentada até 5 vezes quando comparada com a utilização total de um CPU topo de gama.

Symmetry Conservation in General Relativity. An Application of the Initial Value Problem
2023-12-05 15:00 - 17:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Neste documento trata-se o problema do valor inicial (PVI) em Relatividade Geral (RG), bem como algumas das suas aplicações. São discutidos alguns formalismos matemáticos necessários - folheações, resultados sobre equações diferenciais parciais em espaços tempos curvos, e spinors. Com estas ferramentas, esboçam-se os traços gerais do PVI e alguns dos principais resultados na área, tais como o teorema de Choquet-Bruhat para a existência e unicidade de desenvolvimentos de Einstein em vácuo e o subsequente enfraquecimento das condições de regularidade dos dados iniciais, feito por Planchon e Rodnianski. Segue-se uma discussão acerca da estrutura causal destes desenvolvimentos de Einstein, bem como da inclusão de matéria através do tensor de energia-momento e de torção na conexão, generalizando-se resultados disponíveis na literatura. Passa-se de seguida ao estudo da questão da conservação de simetria de Killing no desenvolvimento de dados iniciais, obtendo-se uma equação de propagação hiperbólica e não-homogénea para a derivada de Lie da métrica enquanto quantidade zero. Analisa-se o termo não-homogéneo em pormenor - uma colineação do tensor de Ricci - e apresentam-se dois exemplos de campos de matéria, um dos quais admite conservação da simetria com condições relativamente fracas - o campo escalar massivo de Klein-Gordon - e outro - o campo eletromagnético - que requer restrições mais fortes para garantir preservação da simetria. Termina-se discutindo um tópico semelhante: o problema de valor inicial para twistors, spinors de Killing. Estuda-se a propagação da chamada equação dos twistors em variedades planas, usada para obter uma caracterizar espaços-tempos de Minkowski e de ondas planas ao nível das condições iniciais.

Magnetic Sensor qualification in an industrial environment
2023-12-05 16:00 - 18:00 | Sala C10 Pavilhão Central, Piso 1
Os sensores de magnetorresistência anisotrópica são fundamentais em várias aplicações devido ao seu baixo consumo de energia, escalabilidade e rentabilidade. Contudo, esta tecnologia estagnou nos últimos anos, sendo necessário explorar caminhos alternativos para a sua otimização. Este estudo focou-se na otimização de sensores AMR de permalloy Ni0.8Fe0.2 para aplicações de posicionamento, atualmente em produção no INESC MN, através de diversas técnicas. A avaliação da transição do sistema N3000 para o N3600, que tem um potencial de aumento no rendimento de 78%, revelou características semelhantes entre as amostras, validando então esta mudança. A inclusão de uma camada de buffer de Ta melhorou as propriedades cristalinas, mas levou a uma diminuição do AMR. Contrariamente, em amostras sem buffer,annealing magnético melhorou as propriedades cristalinas e magnéticas, especialmente em temperaturas mais baixas. Valores de AMR de 2,24% e 2,29% foram atingidos, permitindo estabelecer uma correlação entre o crescimento do grão e o aumento deste parâmetro. Camadas de dusting de Pt, sem annealing, melhoraram o valor de AMR de 2.04\% para 2,20\%, enquanto as de MgO resultaram numa diminuição. Após, amostras com Pt mostraram resistividade aumentada e AMR mais baixo. Em contraste, camadas de MgO com t>1nm mostraram-se promissoras na otimização do desempenho dos sensores, atingindo valores de AMR até 2,49% após 5h a 370⁰C. À luz dos resultados, a incorporação de camadas de dusting de Pt e MgO surge como uma via promissora para adaptar o comportamento e desempenho dos sensores AMR, abrindo caminho para futuras inovações no campo da tecnologia de dispositivos magnéticos.

Sensitivity of MARTA Station at the Pierre Auger Observatory to Extensive Air Shower Particle Energy Distributions
2023-12-06 08:30 - 10:00 | Online
Uma estação de deteção de superfície (SD) no Observatório Pierre Auger equipada tanto com MARTA (Muon Array with RPCs for Tagging Air showers) como com um detetor de cintilação de superfície (SSD) oferece a oportunidade de realizar novos tipos de medições de raios cósmicos a altas energias. Este trabalho explora a possibilidade de utilizar uma estação que se encontre nestas condições para realizar uma medição da distribuição de energia das partículas de cascatas atmosféricas (EAS), para as componentes eletromagnéticas e muónicas da cascata.Neste trabalho é desenvolvido um método que permite modificar a distribuição de energia original obtida a partir das simulações e utilizá-la para testar a sensibilidade dos detetores. Aqui demonstra-se que tanto o SD quanto o detetor de RPC (acrónimo para Resistive Plate Chambers) são sensíveis a modificações na região de altas energias da distribuição eletromagnética, especialmente em casos em que a estação se encontra próxima do centro da cascata. Por outro lado, o SSD é insensível à modificação desde que a modificação conserve o número total de partículas na distribuição. Os resultados para a distribuição de muões são, no entanto, inconclusivos. Em regiões distantes do centro da cascata, o baixo nível estatístico das distribuições de muões é preocupante, uma vez que pode estar a afetar a qualidade da modificação do espectro. A análise aqui realizada é idealizada em função da estação Peter Mazur localizada no Observatório Pierre Auger, pois é atualmente a única estação equipada com o MARTA.

Quantum Fluids of Light and Brownian Dynamics on Bose-Einstein Condensates
2023-12-06 10:00 - 11:00 | Sala P3 Pavilhão de Matemática, Piso 1
ResumoInterações fotão-fotão no vácuo têm uma secção eficaz desprezável, em regimes de baixas energias. No entanto, na presença de um meio não-linear desfocalizante do tipo Kerr, como um vapor quente de rubídio, ou de outro metal alcalino, o campo de polarização elétrica atua como um mediador de interações, assumindo um papel importante nestes sistemas. O comportamento coletivo entre fotões é previsto através de uma formulação hidrodinâmica, justificando a designação de fluidos quânticos de luz. Devido às semelhanças entre a equação não-linear de Helmholtz e a equação de Gross-Pitaevskii, bem conhecida na teoria de condensação de Bose-Einstein, prevê-se que os fluidos quânticos de luz sejam bons simuladores de condensados de Bose-Einstein, funcionando a altas temperaturas, sendo assim uma opção mais barata e menos complexa na sua construção e manutenção. Apesar da semelhança formal, é importante salientar as suas diferenças, sendo estas aqui também exploradas. A configuração experimental de uma experiência de fluidos quânticos de luz é detalhada, começando pela estrutura atómica do rubídio até todos os diferentes componentes para o controlo dos parâmetros relevantes, nomeadamente a unidade de controlo de temperatura que surge para controlar a densidade do vapor. A dinâmica de uma impureza num condensado de Bose-Einstein foi estudada na presença de ruído quântico. Os resultados simulados numericamente para uma impureza tipo vórtice são discutidos com as condições necessárias para conduzir um movimento superdifusivo.

QGP effects on Energy Correlators inside jets
2023-12-06 10:00 - 12:00 | Online
O estudo do Plasma de Quarks e Gluões (QGP), a fase desconfinada da Cromodinâmica Quântica (QCD), constitui atualmente uma área de investigação muito ativa e em rápido desenvolvimento. O QGP é a fase do Universo no seu primeiro microssegundo de existência, podendo também ser formado em colisões de iões pesados ultrarelativistas. Nessas experiências, jatos - sprays colimados de hadrões - podem ser formados, constituindo uma ferramenta crucial para estudar o QGP, feito por análise das suas modificações ao viajar pelo plasma, por sua vez conseguido através da comparação com jatos em colisões Protão-Protão, que evoluem no vácuo. Uma das principais manifestações da interação dos jatos com o QGP é uma perda de energia significativa. Outra manifestação crucial é chamada de resposta do meio, constituindo um acréscimo de partículas decorrentes do QGP, que são reconstruídas dentro do jato final. Neste trabalho, funções de correlação de energia, uma nova classe de observáveis, foram calculadas para jatos em colisões de iões pesados e analisadas. As funções de correlação evidenciaram as diferentes fases da QCD pelos quais os constituintes dos jatos passam, e a análise de modificações desprezando a resposta do meio apresentou um comportamento compatível com a ideia de que jatos que evoluem no QGP hadronizam numa escala de tempo posterior à de jatos que evoluem no vácuo. Essas funções de correlação também se mostraram sensíveis à resposta do meio, com sensibilidades diferentes considerando diferentes versões da função.

Equipartition and Entanglement - Relation between ergodicity measures
2023-12-06 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Similarly to the ergodicity hypothesis in classical chaotic systems, in the quantum setting there is asimilar concept, related to quantum thermalization and equipartition over degrees of freedom anddubbed as the eigenstate thermalization hypothesis. This concept is very useful as it provides a linkbetween classical and quantum chaos. The concept of multifractality of quantum wave-functions is away to break the above ergodicity in terms of chaotization and equipartitioning over degrees offreedom in quantum systems. On the other hand, in quantum information theory it is the entanglemententropy which represents the main measure of ergodicity and thermalization. On the third side, in theeigenstate thermalization hypothesis the fluctuations of local observables and their scaling with thesystem size play the central role. In this talk I will represent an exact relation between the above threemeasures, namely multifractal dimensions, scaling of fluctuations of local observables and the (Renyi)entanglement entropy. I will show that the fractal dimension of the non-ergodic wave function puts anupper bound on its entanglement entropy [1]. I will also provide a couple of explicit examplesdemonstrating that the entanglement entropy may reach its ergodic (Page) value when the wavefunction is still highly non-ergodic and occupies a zero fraction of the total Hilbert space. If time permitsI will briefly discuss some other possible deviations from ergodicity relevant for the chaotic many-body.

Energetics of Trapped-Ion Quantum Computation
2023-12-06 17:00 - 19:00 | Online
A computação quântica recorre a fenómenos da mecânica quântica para resolver problemas demasiado complexos para os computadores clássicos. O entusiasmo em torno das suas potenciais aplicações tem levado a um investimento crescente de recursos para o desenvolvimento de computadores quânticos escaláveis com desempenhos temporais cada vez melhores. A questão da eficiência energética dos computadores quânticos, no entanto, apenas ganhou alguma atenção recentemente. Ainda está em falta uma compreensão exacta dos recursos necessários para operar um computador quântico com o desempenho computacional pretendido e da forma como os requisitos energéticos podem afetar a escalabilidade. Nesta tese, foi estudada uma implementação do algoritmo para a transformada de Fourier quântica numa plataforma de iões confinados. O principal objetivo foi a obtenção de uma caracterização teórica dos custos energéticos da computação quântica, investigando o consumo de energia dos diferentes elementos de um computador quântico de iões confinados. O algoritmo foi simulado e, incluindo diferentes modelos de ruído na simulação, o seu desempenho na presença de ruído quântico foi analisado. O custo energético da experiência foi estimado através da análise dos seus diferentes componentes e das etapas envolvidas numa computação quântica, desde o arrefecimento e preparação dos iões até à implementação do algoritmo e medição do resultado. Um potencial dimensionamento dos custos energéticos foi discutido e utilizado para procurar um possível limiar para uma vantagem energética quântica sobre os supercomputadores clássicos.

Radiosensitizers for Cancer Radiation Therapy
2023-12-06 17:30 - 19:00 | Sala P12 Pavilhão de Matemática, Piso 2
A radioterapia é um tipo de tratamento do cancro essencial, cuja eficiência pode ser melhorada com o uso de radiosensibilizadores. Estes compostos são administrados em simultâneo com radiação ionizante, aumentando assim a sensibilidade das células aos efeitos nocivos da radiação. Por essa razão, investigar radiossensibilizadores é fulcral para otimizar o tratamento de cancro. A presente tese avaliou a capacidade de dois novos compostos, PDS-pz e Re-PDS-pz - ligandos G-quadrúplex (G4) sintetizados no C2TN - de se comportarem como radiossensibilizadores, em células do cancro da próstata (na linha celular PC3). Este possível comportamento foi estudado através de ensaios experimentais biológicos e radiobiológicos e de simulações de Monte Carlo. Os efeitos dos compostos PDS-pz e Re-PDS-pz foram comparados aos do composto comercial e conhecido radiossensibilizador RHPS4. As células analisadas foram irradiadas, em diferentes estudos, com raios gama de cobalto-60 em doses de 0,5 Gy a 6 Gy. Os ensaios experimentais demonstram aumento da citotoxicidade nas células aquando da administração dos compostos estudados e maior efeito nocivo aquando da atuação simultânea destes com a radiação - o que confirma o comportamento radiosensibilizador do PDS-pz e do Re-PDS-pz. O trabalho computacional foi elaborado com sucesso, que validou o débito de dose de 1 Gy/min, emitido pelo irradiador Precisa-22, e descreveu o comportamento temporal das espécies reativas de oxigénio (ROS) criadas após irradiação.

Bridging the gap between modeling and experiments in low temperature plasmas
2023-12-07 11:00 - 13:00 | Anfiteatro PA1, Piso -1 - Pavilhão de Matemática, Campus da Alameda
Abstract: Low-temperature plasma (LTP) science and technology have become integral to numerous applications with far-reaching implications for our society. From advancing microelectronics industry through plasma–surface interactions and microprocessor fabrication to enabling electric propulsion systems for satellite motion control, LTPs play a pivotal role in diverse fields. The continuous evolution of LTPs has given rise to novel application areas, including multidisciplinary research domains such as plasma agriculture, plasma catalysis and plasma-based gas reforming. Despite these advancements, understanding and controlling non-equilibrium plasma processes remain challenging due to the need to identify key phenomena operating across spatial and temporal scales spanning several orders of magnitude.This seminar will explore ongoing efforts dedicated to understanding the key role played by parameters of relevance (electric field, vibrational excitation, gas heating, etc.) in LTPs. The presentation will be particularly focused on plasma-based applications targeted at converting pollutant gases into value-added products, offering sustainable alternatives to fossil fuels, thereby contributing to the decarbonization of energy systems. I will discuss past, current and future activities aimed at advancing our understanding of LTPs by closing the gap between modeling and experimental results. The talk will also underscore the challenges associated with establishing benchmark experiments for model validation and simplifying complex plasma kinetic schemes.

Optimization of Magnetic Tunnel Junctions for low noise applications
2023-12-07 14:00 - 16:00 | Online
Este trabalho explora sensores túnel magnetoresistivos (TMR) que desempenham um papel fundamental em medições magnéticas devido ao seu alto desempenho, consumo eléctrico, sensibilidade e capacidade de deteção de baixos campos magnéticos, com aplicações em medições magnéticas no espaço ou magnetofisiologia. No entanto, necessitam de dispositivos capazes de detetar campos magnéticos na ordem dos pT. Uma possível estratégia para garantir deteção destes campos magnéticos consiste em 3D packing de sensores TMR, que sobrepostos verticalmente em níveis completos, permitem a obtenção de uma melhor detetividade. Neste caso, efeitos de topografia passam a ter um papel relevante e diferentes estratégias foram introduzidas no design de sensores para avaliar o seu efeito. Um tratamento de feixe de iões de O2 foi estudado, com o objetivo a aumentar o rendimento do processo de fabricação de sensores. A redeposição metálica durante a definição do pilar leva a uma redução de MR, e, por isso, a uma menor sensibilidade. A estratégia desenvolvida pode contribuir para a melhoria dos processos de fabricação no INESC MN.

On the Cauchy problem in effective field theories of gravity
2023-12-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT:Effective field theory (EFT) provides a way of parameterizing strong-field deviations from General Relativity that might be observable in the gravitational waves emitted in a black hole merger. To perform numerical simulations of black hole mergers in an EFT, it is necessary that the theory admits a well-posed initial value formulation. In the first part of my talk, I will review recent results on the initial value formulation of gravitational EFTs (beyond General Relativity) with second-order equations of motion. In the second part, I will discuss some ideas to deal with EFTs with higher derivative equations.

Engineering MnNi bilayers for optimal MTJ sensors temperature resilience
2023-12-07 16:00 - 18:00 | Online
As aplicações para sensores magnetoresistivos, como junções de efeito túnel (JET), têm crescido constantemente, com necessidade de maior resiliência térmica e maior alcance de condições para aplicações na faixa de pico a militesla. O presente trabalho mostrou MnNi ser um candidato viável para um AFM em bicamadas exchange coupled de sensores JET, com a tecnologia IBAD superando os resultados da IBD, maximizando o campo de exchange bias e a temperatura de blocking.O trabalho realizado no INESC MN permitiu a deposição, medição e fabricação de sensores JET. Estudos de espessura de bicamada foram realizados, com melhores resultados alcançados para camadas espessas de MnNi (>40nm), e IBAD permitiu uma melhoria de 160Oe para 1046Oe de exchange bias. Estudos de temperatura de annealing mostraram melhores condições para 2h a 300°C. A análise de AFM e XRD mostrou que IBAD reduz a rugosidade superficial do AFM, facilitando o correto crescimento cristalino das camadas superiores, com uma diminuição simultânea de 16\% no tamanho do grão. Tb de 300°C~310°C foi encontrado para bicamadas MnNi-IBAD, e Tb de 424°C para IBD. Fenómenos incomuns como um aumento inicial em Hex com a temperatura e uma diminuição acentuada de Hex perto de Tb foram observados.Sensores JET microfabricados foram caracterizados com equipamentos VSM e R(H). Uma diminuição efetiva do exchange bias foi observada para amostras IBAD, e em ambas as amostras nenhuma anisotropia de forma cruzada foi alcançada, com a camada de referência não definida. Foi observado um deslocamento da curva R(H), sensores funcionais foram mapeados e valores baixos de MR de 0.76% foram alcançados, com melhores resultados para pilares retangulares do que elípticos.

Information Diffusion on Dynamic Networks
2023-12-07 16:00 - 18:00 | Online
Nos últimos anos, a comunidade científica tem vindo a acumular provas conclusivas do aumento da polarização.Este crescimento não só implica que diferentes grupos não consigam chegar a um consenso sobre questões fundamentais, como também se materializa em redes sociais mais modulares - estruturas formadas por comunidades fracamente ligadas - que exacerbam os riscos de polarização, mesmo em tópicos menos divisivos. Para abordar esta questão, trabalhos anteriores priorizaram a identificação dos mecanismos subjacentes responsáveis pela polarização social, tanto na composição das opiniões como no que respeita à organização estrutural das comunidades.No entanto, que impacto tem a co-evolução de um processo de difusão de informação e da estrutura da rede em populações que já se encontram estruturalmente polarizadas? Será que amplifica ou atenua o grau de polarização estrutural numa comunidade? Neste trabalho, é utilizado um modelo co-evolutivo de difusão de informação para compreender o impacto que as preferências individuais de religação têm nas estruturas modulares e em que condições esta dinâmica de adaptação da rede pode levar a estrutura social a atingir um consenso.Demonstra-se que os indivíduos com preferências de religação homofílicas promovem o consenso para uma informação simples, ao passo que os indivíduos com preferências de religação heterofílicas são mais eficientes na criação de pontes entre populações no caso de uma informação complexa.Estes resultados sugerem que, em redes sociais polarizadas, uma combinação de indivíduos com diferentes preferências de religação parece ser essencial para atenuar a polarização social.

Proca field perturbations in higher-dimensional AdS and Schwarzschild-AdS spacetimes
2023-12-11 13:00 - 15:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)/Online
Perturbações de campos em espaços-tempo com buracos negros são consideradas em vários contextos, desde a investigação da dinâmica de buracos negros astrofísicos até ao estudo de teorias de gravidade quântica. Um espaço-tempo perturbado vibra com frequências características, conhecidas como modos quasi-normais. Em espaços-tempo assimptoticamente anti-de Sitter (AdS), estes são estudados no contexto da correspondência AdS/teoria de campo conformal (CFT), onde as frequências dos modos quasi-normais determinam a escala de tempo da termalização da CFT.Nós estudamos perturbações de campos de Proca em espaços-tempo AdS e Schwarzschild-AdS com d-dimensões. Obtemos as equações de Proca decompondo o campo segundo o seu comportamento tensorial na esfera. Demonstramos que as equações formam dois setores completamente separados: o setor tipo-vetorial, que engloba d-3 graus de liberdade desacoplados do campo, governados por uma única equação do tipo-onda; o setor tipo-escalar, que descreve os restantes dois graus de liberdade do campo, governados por duas equações do tipo-onda acopladas. Nós mostramos que as últimas desacoplam em AdS com d dimensões, e calculamos as soluções exatas de modos normais para perturbações de Proca neste espaço-tempo, impondo condições de fronteira de Dirichlet no infinito. Adicionalmente, recuperamos os resultados para perturbações de Maxwell quando a massa do campo de Proca tende para zero. A estabilidade linear em Schwarzschild-AdS perante perturbações de Proca tipo-vetorial e monopolo é provada. Também calculamos numericamente os modos quasi-normais de perturbações de Proca em Schwarzschild-AdS com 4,5,6,7 dimensões, e desenvolvemos um estudo analítico do espetro para buracos negros pequenos.

Quantum Simulation Exploiting the Haag-RuelleScattering Theory
2023-12-11 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The last years have seen a rapid development of applications of quantum computationto quantum field theory. The first quantum algorithms for simulation of scattering havebeen proposed in the context of scalar and fermionic theories, requiring thousands oflogical qubits. These algorithms are not suitable to simulate scattering of incomingbound states, as the initial state preparation relies typically on adiabaticallytransforming wavepackets of the free theory into wavepackets of the interactingtheory. In this talk, I will present a strategy to excite wavepackets of the interacting theorydirectly from the vacuum of the interacting theory, allowing for preparation of statesof composite particles that can be taken as initial states of a scattering simulation. Thisis the first step towards digital quantum simulation of scattering of bound states.The approach is based on the Haag-Ruelle scattering theory, which provides a way toconstruct creation and annihilation operators of a quantum field theory in a full, nonperturbative framework. As an example, I will consider a scalar theory in one spacedimension displaying a composite particle in its spectrum

Strong gravity frontier of particle physics
2023-12-12 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: In the vicinity of black holes, particle density can significantly increase, acting as efficient transducers. This is evident in the superradiant generation of ultralight bosons, which can attain Planck-scale field values. Within this dense boson environment, we witness the occurrence of non-perturbative particle production—a phenomenon previously associated primarily with the early-universe cosmology. This talk will explore their impact on various observational channels associated with black holes, such as the high-energy neutrino observatories and Event Horizon Telescope.

MUSE-Faint: Dissecting the faintest galaxies with MUSE
2023-12-14 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: Ultra-faint dwarfs are the lowest mass and most dark-matter dominated systems known. The shallow potential wells make them susceptible to feedback from star formation and their low baryonic content allows us to use their stars as test-particles in the dark matter potential. Here I will give an overview of the MUSE-Faint survey, a MUSE GTO survey of 10 ultra-faint dwarfs. After introducing the survey, I will outline how the high density of stellar spectra obtainable with MUSE can be used to constrain the dark matter content and density profiles of the galaxies and discuss how the data can be used to constrain dark matter models and the details of galaxy formation models in the very most star poor dark matter halos known.

Let's talk about... Applications of Particle Physics research
2023-12-14 17:00 - 19:00

Plasmas in the semiconductor industry: modern trends, opportunities and diversity
2023-12-15 11:00 - 12:00 | Room 02.1 (floor -2, Centro de Congresso IST)
Abstract:The semiconductor industry is moving towards ever increasing densities and ever decreasing feature sizes. This was kicked off 40 years ago, by two international initiatives: Sematech in the USA and JESSI in the European Union. Those initiatives have lasted for around 10 years. After that, the technology was mature, and industry hardly needed the input of academia for solving their technical challenges in the plasma domain. In recent years, since the moment that feature sizes came below 10 nm, a revival of the field has been taking place. For example: vertical etching angle specifications ask for side wall angles between 89.6 and 90 degrees, anisotropy has been approaching and now exceeds 100, etc. This has evoked a new need of industry for input from plasma physics, sheath physics, fluid dynamics and surface physics and chemistry in these size regimes (Knudsen flow, single atom reactions, etc). Recently, the USA launched the CHIPS act, a package of 45 G$ for semiconductor processing technology. Europe has a similar CHIPS-package. In the presentation the needs of modern-day semiconductor processing will be highlighted, and we will also try to show how we, as people in academia, can cater to that need while at the meantime performing cutting edge fundamental science. One of the needs of the industry, but also of academia, is diversity. We need a well-trained workforce with a diverse composition. TU/e has embarked on a course of increasing the diversity in the academic population. With that strategy, for instance, the fraction of female staff in tenured academia increased from 2 % to 35 % in 6 years in the physics department. We will describe the vital steps that have contributed to this spectacular shift.

Techno-Economic Analysis of Space Heating and Cooling Systems with Solar Energy for Non-Residential Buildings
2023-12-15 14:00 - 16:00 | Online
As alterações climáticas são causadas, sobretudo, pela queima de combustíveis fósseis para satisfazer as nossas necessidades energéticas. Os edifícios são o maior consumidor de energia na UE, sendo responsáveis por 40% da energia que esta consome e por 36% das emissões de gases de efeito estufa relacionadas com energia, logo NZEBs são necessários. Neste trabalho, em Polysun, fizemos uma análise técnico-económica a um sistema de aquecimento e arrefecimento com bomba de calor em quatro edifícios não-residenciais que variam em tamanho (pequeno e médio) e condição (não-renovado e renovado), considerando a inclusão de energias solar térmica e fotovoltaica. Devido à dificuldade em combinar energia solar térmica com a bomba de calor, foi necessário requisitar água quente ao sistema para este satisfazer as necessidades energéticas dos edifícios. No entanto, o sistema não é viável economicamente. Pelo contrário, o sistema solar fotovoltaico é viável mesmo considerando apenas as necessidades de climatização dos edifícios. Definir uma temperatura de aquecimento diferente quando o edifício não é ocupado melhorou o desempenho do sistema, enquanto a mesma abordagem para o arrefecimento originou resultados inconclusivos. Quando consideramos o consumo global de eletricidade dos edifícios, os resultados económicos do sistema melhoram, reduzindo os custos totais em 25 anos em 29.7% a 34.3% sem vender eletricidade. Além disso, o sistema fornece entre 47.0% e 99.8% da eletricidade necessária para climatização e entre 51.9% e 66.2% da eletricidade total consumida. Finalmente, os edifícios renovados pequeno e médio têm custos totais 11.8% e 17.1% inferiores aos dos edifícios não-renovados pequeno e médio.

Quantum phases of quasiperiodic matter and why incommensurate moiré is different
2023-12-20 09:30 - 11:00 | Anfiteatro Abreu Faro - Complexo Interdisciplinar
Resumo Uma compreensão profunda de sistemas de matéria condensada foi alcançada assumindo uma periodicidade perfeita, através do teorema de Bloch. No entanto, quando a invariância translacional é quebrada, podem manifestar-se fenómenos surpreendentes que não têm análogo no caso periódico. As estruturas quaseperiódicas, caracterizadas por modulações determinísticas incomensuráveis com a rede, são um exemplo particularmente rico de sistemas não translacionalmente invariantes. Estes sistemas manifestam física intrigante, desde propriedades de localização exóticas a fenómenos de banda estreita correlacionados em estruturas moiré como a bicamada de grafeno rodada. É crucial que, embora seja bem conhecido que as estruturas moiré são quase-periódicas em geral, só recentemente o papel da quase-periodicidade começou a ser explorado nestes sistemas. Nesta dissertação exploramos as fases quânticas de estruturas quase-periódicas e moiré de uma forma unificada. Começamos por explorar as propriedades de localização de modelos quase-periódicos de rede genéricos. Primeiramente, mostramos que transições genéricas de deslocalização-localização em modelos unidimensionais sem interação partilham um mecanismo comum baseado na emergência de dualidades ocultas entre as fases estendida e localizada. Adicionalmente, desenvolvemos uma descrição universal das propriedades de localização destes sistemas e usamo-la para capturar analiticamente diagramas de fase de localização para uma ampla classe de modelos. Por fim, desenvolvemos uma generalização a muitos corpos desta teoria para abordar as propriedades de localização no estado fundamental de Hamiltonianos unidimensionais quase-periódicos com interacções. Finalmente, estudamos o papel da quase-periodicidade em estruturas de moiré. Analisando um modelo de tight-binding da bicamada de grafeno rodada, mostramos que a quase-periodicidade cria uma fase sub-balística no regime de banda estreita não interactuante. Adicionalmente, estudamos um sistema de moiré unidimensional com interacções, que contém uma fase multifractal crítica muito semelhante à fase sub-balística da bicamada de grafeno rodada. Mostramos que, apenas quando o sistema é quase-periódico, esta fase é instável à criação de uma nova fase ordenada após a adição de interacções. Esta dissertação oferece duas contribuições principais. Por um lado, fornece uma compreensão unificada de diferentes modelos de rede quase-periódicos e um novo conjunto de ferramentas para estudar os seus diagramas de fases. Por outro lado, ao estabelecer a quase-periodicidade como um possível ingrediente importante nos sistemas moiré e o seu potencial para criar novos estados da matéria, marca o início da exploração de possibilidades excitantes ainda por descobrir no campo emergente dos sistemas de moiré quase-periódicos.

Development of a microfluidic sample preparation system for bacteria magnetic labelling
2023-12-20 14:00 - 16:00 | Online
A microfluídica surgiu como uma ferramenta que permite a miniaturização de processos laboratoriais e o desenvolvimento de dispositivos Lab-On-a-Chip (LOC). Estas plataformas em microescala oferecem vantagens significativas, incluindo volumes reduzidos de amostras e reagentes, automatização de processos e resultados rápidos e reprodutíveis.Os métodos tradicionais de marcação magnética tipicamente envolvem o uso de vários instrumentos laboratoriais especializados, resultando em tempos prolongados (numa escala de horas/dias) desde a recolha de amostra até à sua análise - uma preocupação significativa em situações que envolvem ameaças biológicas, como o antraz, a tuberculose e a legionelose. Este trabalho, que faz parte de um projeto a decorrer no INESC MN, enfrenta esse desafio introduzindo um circuito microfluídico para preparação de amostras, que é compacto (largura_38650×altura_50×comprimento_50320 μm3) e consegue completar o processo de marcação magnética em menos de 5 minutos, tornando-o adequado para aplicações de point-of-care (POC).Dentro deste circuito, duas suspensões - a amostra biológica e nanopartículas magnéticas – são introduzidas e interagem dentro de um misturador (l_12600×a_50×c_18240 μm3, com obstáculos) para ligação das nanopartículas aos analitos biológicos, ostentando uma eficiência de mistura simulada de >99%. O uso subsequente de um separador magnético (l_5650×a_50×c_23740 μm3) curva a trajetória das espécies magnéticas, tendo-se obtido um resultado de >80% de conteúdo de ferro que flui através do circuito em comparação com o descartado como resíduo. Esta separação seletiva elimina com sucesso analitos não marcados. A amostra marcada magneticamente entra depois num separador por dimensões (l_800×a_50×c_8450 μm3, com obstáculos), refinando ainda mais o processo e separando os analitos marcados de nanopartículas magnéticas livres, que são significativamente menores. Depois da amostra marcada passar por este circuito, esta segue para o citómetro magnético para análise. Pretende-se com esta abordagem integrada oferecer uma solução rápida e eficiente para preparar e analisar amostras biológicas marcadas magneticamente. Ao reduzir a complexidade do processo de preparação de amostras e facilitar a integração com, por exemplo, um coletor de aerossóis e um citómetro magnético, este sistema possui grande potencial em aplicações POC em saúde pública, monitorização ambiental, entre outros.

Quantum simulation of quasicrystals with ultracold quantum gases: The Bose side
2023-12-20 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Quasicrystals, an exotic class of materials with long-range but nonperiodic order,exhibit fascinating properties due to their unique position at the crossroads of longrange-ordered and disordered systems. These include remarkable localization andfractal properties. Quantum simulation of quasicrystals in synthetic bosonic matternow paves the way to the exploration of these intriguing systems in wide parameterranges. This talk will review recent progress in the field of quantum simulation ofquasicrystals with ultracold-atom gases. Particular attention will be paid to theemergence of the still-elusive Bose glass phase. Previously, clear observation of thisemblematic phase has been thwarted by thermal fluctuations, which compete withquasi-disorder. But recent work shows that the use of shallow quasicrystal potentialspermits to overcome this pitfall, and Bose glass phases can be stabilized in broadtemperature regimes, in 1D as well as 2D. Theoretical aspects and experimentalperspectives will be discussed.

Let's talk about... Plasma-based conversion of greenhouse gases
2023-12-21 17:00 - 19:00

Non-local couplings: A new technique to enhance quantum annealing through distribution
2024-01-03 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Quantum Annealing has proven to be a powerful tool to tackle several optimizationproblems. However, its performance is severely impacted by the limited connectivityof the underlying quantum hardware, compromising the quantum speedup. In thiswork, we present a novel approach to address these issues, by describing a method toimplement non-local couplings throught the lens of Local Operations and ClassicalCommuncations (LOCC). Non-local couplings are very versatile, harnessing theconfigurability of distributed quantum networks, which in turn lead to greatenhancement of the physical connectivity of the underlying hardware. Furthermore,the realization of non-local couplings between distrinct quantum annealing processorsactivates the scalability potential of distributed systems, i.e. allowing for a distributedquantum annealing system. Finally, in a more distant vision, we also show that securemulti-party quantum annealing algorithms are possible, allowing for cooperation ofdistrusting parties through optimization with quantum annealing and a particular typeof non-local couplings.

Hydrodynamics of Multipole-Conserving Systems
2024-01-08 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
During this talk, we will explore how conserving quantities influence the long-timedynamics of generally strongly interacting closed systems. Typically, interactingquantum systems achieve thermalization via their own unitary dynamics, leading tothe emergence of statistical mechanics. However, the route to equilibrium can differdue to the existence of conserved quantities. Often, conserved charges spread diffusively across the system. However, mobilityconstraints can impede or even halt their dynamics. The initial part of the talk isdevoted to the non-equilibrium dynamics of fractonic systems, especially those withmultiple conservation laws, such as dipole conservation. In these systems, charges areunable to move independently. Their limited dynamics are described by a generalizeddiffusion equation that exhibits sub-diffusion [1]. In the second half of the talk, inspired by recent experiments on trapped-ion platformsthat intrinsically display power-law decaying interactions [2], we will delve into theinterplay between long-range interactions that promote thermalization and the dipolemobility constraints that obstruct it [3].

PARTICLE AND NUCLEAR PHYSICS EXPRESSIONS OF INTEREST
2024-01-10 15:00 - 18:00 | Anfiteatro PA1, Piso -1 - Pavilhão de Matemática, Campus da Alameda

Signals and constraints on Multi-Higgs models
2024-01-17 09:00 - 11:00 | Online
Em alguns dos mais importantes problemas por resolver na física de partículas, a resposta mais provável surge da adição de novas partículas ao Modelo Padrão. Novos bosões de Higgs são frequentemente o ponto de partida para novos modelos. Estes, por sua vez, precisam de ser limitados teoricamente através da unitariedade nas teorias quânticas de campo, quer por limites de parâmetros, quer por regras de soma de amplitudes. Introduzimos um novo método computacional para estabelecer limites de unitariedade em modelos escalares e calculamos esses limites em modelos de três dubletos de Higgs. Recorremos a regras de soma de unitariedade em modelos de fotões escuros descobrindo que a unitariedade define um novo parâmetro de precisão. Com ele, restringimos os modelos de mat´eria escura, apontando para uma dependência específica entre a física do bosão Z e a estrutura do novo sector escalar. Em muitos casos, os modelos de matéria escura podem ser excluídos. Estudamos a teoria invariante no contexto de modelos de multiplos dubletos de Higgs, calculando a série de Hilbert do modelo de trˆes dubletos de Higgs pela primeira vez usando o cálculo Omega. Encontramos vários resultados da teoria dos invariantes aplicáveis a modelos de múltiplos dubletos de Higgs, tais como a contagem de parâmetros nos casos geral e simétrico. Finalmente, usamos a teoria dos invariantes para estudar o puzzle de sabor do Modelo Padrão. O enigma do sabor é reformulado num quadro completamente invariante e simplificamos resultados anteriores sobre as relações entre os invariantes que violam CP, e os que não violam CP. O trabalho sobre estas duas classes de tópicos (limites de unitariedade e teoria dos invariantes) resultou numa série de publicações que vão desde propriedades matemáticas abstratas que restringem as teorias físicas ate `a comparação pormenorizada com a experiencia.

"Non-Unitary 3 x 3 Mixing in Majorana Neutrinos and Vector-like Quark Models"
2024-01-18 11:00 - 13:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)

From Hubble to Bubble - gravitational waves from phase transitions after inflation
2024-01-18 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
ABSTRACT: The prospect of a stochastic gravitational wave (GW) background from the primordial universe offers a promising new window for cosmology and fundamental physics. Studying the GW signals from cosmological phase transitions can illuminate aspects of Beyond the Standard Model (BSM) physics and allow us to probe the early universe via a new perspective. In this study (2309.08530), we investigated minimal scalar BSM extensions, with respect to the evolution of the scalar potential at the end of inflation. More specifically, we focussed on the transition from the typical potential-dominated de Sitter epoch to the kinetic dominated period dubbed kination. In this setting, a strong first-order phase transition can take place because of the scalar field's decreasing potential barrier due to its non-minimally coupling to gravity. Therefore, a characteristic GW spectrum can be produced from the collision of true-vacuum bubbles. With this prescription, we propose a new triggering mechanism for BSM phase transitions that could produce potentially observable GW signatures with the future detectors.

FLEXIBLE TRIBOELECTRIC NANOGENERATORS FOR A SELF CHARGING SYSTEM IN MOBILE ELECTRONICS
2024-01-22 09:00 - 11:00 | Sala P12 Pavilhão de Matemática, Piso 2
Abstract: Textile triboelectric nano-generators (TENGs) are promising solution for wearable, self-powered sensing technology. However, to develop textile TENGs with high output power in adaptable devices using industrial textile compatible techniques for embedded textile electronics is still challenging. In this work, a flexible triboelectric textile is developed by using printed graphene electrodes and the textile as a triboelectric pair with different deposition methods. The flexible TENG exhibits steady output performance under heavy deformation and their sensitivity to movement was investigated as a wearable sensor to monitor biomechanical movements. This work paves the door for the seamless incorporation of self-powered wearable sensing technology into textiles by offering a flexible method for creating flexible triboelectric textile fabrics using industrially suitable printing textile processes.

Properties of the hosing and self-modulation of long particle beams in overdense plasma
2024-01-23 09:00 - 11:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
A aceleração baseada em plasma (ABP) poderá reduzir significativamente a dimensão e/ou o custo dos colisores de partículas, que têm sido instrumentais para obter descobertas fundamentais na física e cujos limites técnicos se está a tornar cada vez mais dispendioso desafiar. Os conceitos de ABP dependem frequentemente da capacidade de manipular interações complexas entre feixe e plasma. Num desses conceitos, direcionado a aplicações na física de alta energia e que está a ser testado na experiência AWAKE no CERN, a onda de plasma usada para aceleração é impelida por um feixe de partículas longo e altamente energético. Neste caso as interações em causa são as instabilidades de hosing e de automodulação. A instabilidade de auto-modulação (IAM) pode ser utilizada para produzir campos de esteira (wakefields) de alta amplitude a partir de um feixe longo, que de outra forma não seria adequado para excitar a onda de plasma. A instabilidade de hosing (IH) é indesejada, porque pode deteriorar o feixe e a estrutura do campo de esteira. Nesta dissertação, começamos por rever e alargar a teoria que descreve estas instabilidades. Utilizamos simulações particle-in-cell com o código OSIRIS para testar a robustez da IAM, especialmente após a sua saturação, a flutuações das condições iniciais. A dependência das taxas de crescimento da IH e da IAM da frequência de perturbação é determinada para um regime adiabático e um regime inicial. Durante este regime inicial, mostramos que ambas as instabilidades podem ser interpretadas como osciladores harmónicos forçados, e que é possível controlar o seu crescimento ao "desafinar" a oscilação do plasma em resposta a uma perturbação do envelope (IAM) ou do centroide (IH) do feixe suficientemente cedo. No caso da IAM revelamos ainda um fenómeno de ressonância sub-harmónica. Todos estes resultados são validados com simulações. Esta nova compreensão do crescimento de instabilidades feixe-plasma pode ter implicações importantes para os aceleradores baseados em plasma.

Multiistochastic operations and convolution channels for quantum states
2024-02-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The notion of convolution of two probability vectors can be extended to operationsdetermined by multistochastic tensors, to describe Markov chains of a higher order. Onthe other hand, the idea of convolution lies in the centre of machine learningalgorithms for image processing: Convolutional Neural Networks. In my talk, I will firstpresent the characterization of the probability eigenvectors of multi-stochastictensors, corresponding to fixed points of generalized Markov chains. Similar results willbe also obtained in the quantum case for multi-stochastic channels acting on mixedquantum states. Next, I propose a quantum analogue of the convolution, based oncoherifications of tristochastic tensors, defined for two arbitrary density matrices ofthe same size. Finally, I will discuss possible applications of this notion to constructschemes of error mitigation or as building blocks in quantum Convolutional NeuralNetworks..

Vibrating string loop around black hole
2024-02-08 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Abstract:A thin circular structure, a string loop, vibrating in the central plane of a Schwarzschild black hole will be investigated. String loop stability and frequencies of its vibrational modes will be provided for different string equations of state. String are objects with tension and hence they can help us to understand the problem of relativistic elasticity; they can be also considered as simplified models for thin magnetic flux tubes from plasma physics. We used the vibrating string loop model to fit the quasi-periodic oscillation observed in X-ray signals coming from some compact sources.

Plasma Light Sources: A Spatiotemporal Analysis
2024-02-09 09:30 - 12:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
As fontes de raios X mais avançadas, tais como os lasers de electrões livres e os sincrotrões, permitem sondar e obter imagens de processos ultra-rápidos que ocorrem às mais ínfimas escalas atómicas e moleculares. Estas fontes são dispositivos de grandes dimensões, normalmente da ordem de alguns quilómetros. Recentemente, têm sido feitos esforços para desenvolver soluções mais pequenas e económicas, maioritaraimente baseadas em feixe-plasma. Nesta tese, exploramos as fontes de radiação baseadas em plasma usando teoria e simulações Particle-In-Cell, baseando-nos nas possibilidades abertas pela recente descoberta da Superradiância Generalizada para propor novos métodos de geração de impulsos de radiação intensos, ultra-curtos e de alta frequência. Nomeadamente, investigámos a radiação proveniente de partículas que atravessam campos evanescentes. Estes modos de superfície são comuns em experiências de interação laser-plasma. Tirámos partido da localização espacial extrema das ondas evanescentes para gerar raios-X dirigidos e demonstrámos que os electrões com g ' 10100 que atravessam uma onda evanescente podem produzir radiação KeV-MeV. Além disso, mostrámos que a posição de intersecção entre o feixe de electrões e a onda evanescente pode atuar como uma partícula virtual. Nas condições certas, esta partícula virtual pode ser superluminosa e produzir um choque ótico superradiante. Além disso, explorámos a radiação coerente de betatrões através de superradiância generalizada. Onde uma manipulação espácio-temporal do feixe de partículas aceleradas pode levar à emissão superradiante. Mostrámos que um feixe de partículas com uma modulação sinusoidal com uma velocidade de fase superluminal pode produzir choques ópticos ao longo do ângulo de Cherenkov associado à velocidade de fase da modulação. Estes choques ópticos conduzem a impulsos ultra-curtos de nível de attossegundo cuja intensidade cresce quadraticamente com o número de partículas no feixe, independentemente da distância entre as partículas. Durante a realização desta tese, baseámo-nos fortemente no RaDiO e introduzimos várias melhorias neste código. Uma das mais importantes foi acompatibilidade com GPU utilizando a linguagem de programação CUDA. Utilizando uma única placa de GPU, conseguimos cálculos de radiação quase instantâneos em milhões de células espaciais, um feito que anteriormente só era possível quando se utilizavam clusters de computadores com centenas de CPUs. Esta melhoria permitiu-nos executar inúmeras simulações de radiação, anteriormente dispendiosas, permitindo observar a radiação a resoluções espaciais sem precedentes.

Multi-messenger physics with the Pierre Auger Observatory and the Southern Wide-field Gamma-ray Observatory
2024-02-14 11:00 - 12:00 | Online (Meeting ID: 989 8981 6004, Passcode: [REDACTED]
Abstract: he Pierre Auger Observatory, the world's largest experiment in the study of the highest energy astroparticles, is currently undergoing an upgrade to enhance its UHE cosmic ray detection capabilities further. On the other hand, the Southern Wide-field Gamma-ray Observatory, a next-generation experiment aiming to look for PeVatron sources in the centre of our Galaxy, is currently on an R&D phase to concept, design and plan its construction at a high altitude in South America. Given the energy overlap between these observatories and their current set of conditions, there is a privileged opportunity to explore strategies to boost the capabilities of the Pierre Auger Observatory and the SWGO in detecting astroparticle multi-messenger phenomena. In this presentation, I will discuss the efforts aimed at enhancing the multi-messenger capabilities of both gamma-ray array observatories. Specifically, I will demonstrate how these observatories can efficiently detect astrophysical neutrinos without incurring additional costs, by leveraging inclined shower events. Additionally, I will illustrate how the energy thresholds of these observatories can be lowered through the implementation of a dedicated trigger strategy. Furthermore, novel gamma/hadron discrimination observables will be introduced, showcasing their ability to surpass muon counting in arrays similar to SWGO, while also exhibiting promising performance in larger, sparser arrays like the Pierre Auger Observatory.

Novel Applications of Plasma-Based Accelerators: from Non-relativistic Particles to Radiation Generation
2024-02-15 10:00 - 12:00 | Online
The past years have seen a growing interest in plasma-based accelerator technology since it provides a route to more compact, ecological yet powerful accelerators. However, even well-established acceleration techniques [1, 2] are only effective with particles traveling at speeds close to the speed of light (relativistic particles), leading to the exclusion of heavier particles (with respect to electrons), e.g. muons [3] or pions from the acceleration process. In this PhD work, we propose an innovative method to fill this gap. We exploit structured light pulses with variable group velocities [4, 5, 6], to demonstrate, with theory and numerical calculations, that such property, combined with a tailored density profile [7] for the plasma, can give us the necessary control over the velocity of the wake to unlock the possibility of accelerating these particles from non-relativistic to relativistic velocities in a single acceleration stage in a plasma accelerator.Furthermore, our ongoing research explores the potential application of plasma-based acceleration technology in coherent radiation production. We investigate the development of instabilities as a long particle beam propagates through a plasma, that is a possible way of generating coherent radiation.

Dynamics of the inboard and outboard density profile at ASDEX Upgrade
2024-02-16 09:00 - 11:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática)
We present our studies of the scrape-off layer (SOL) at ASDEX Upgrade, focusing on the behavior of the inboard SOL in different magnetic configurations and the dynamics of the high-density region near the inboard plasma edge. Understanding SOL behavior is essential to manage heat exhaust and achieve a detached operation in current and future reactors. We investigate the existence of hollow density profiles at the inboard midplane SOL by combining several diagnostics and using a novel interpretation of reflectometry data that relies on analyzing the spectral signatures of the beat signal. We show that the poloidal density asymmetry can influence line-integrated measurements, such as interferometry, and should be included in an integrated data analysis. We investigate the role of the magnetic configuration in shaping the inboard SOL profile, particularly as the plasma approaches a double-null configuration typical of many reactor designs. Our investigations reveal a narrowing of the inboard SOL profile, driven by the magnetic disconnection from the outboard SOL, underscoring the importance of magnetic topology and parallel heat conduction in determining the inboard SOL properties. We see a steep density gradient at the secondary separatrix in both the midplane and divertor regions, which we attribute to the presence of the inboard high-density region, observable using reflectometry and Thomson scattering diagnostics. Near double-null, a drastic reduction in conducted heat to the inboard SOL leads to decreased electron and neutral density in the inboard divertor. Lastly, we observe that the high-density region is significantly suppressed in unfavorable field configurations. We use these scenarios to measure the edge density decay length at the inboard and outboard midplane. We estimate a consistently larger outboard decay length than the inboard side, with an average ratio of 1.7, corroborating the expected ballooning nature of radial transport in tokamaks.

Apples-to-apples comparisons between simulations and observations from UV to mm wavelengths
2024-06-23 15:30 - 17:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Simulações de hidrodinâmica cosmológica são uma ferramenta poderosa no estudo da formação e evolução de galáxias. Para calibrar essas simulações e fazer previsões quantitativas, é necessária uma comparação exata com os dados observacionais.Isto não é trivial: simulações hidrodinâmicas geram propriedades intrínsecas, como massas estelares e SFRs, que não são diretamente comparáveis às propriedades medidas das galáxias observadas. Desenvolvemos a ferramenta de modelagem direta SKIRT para gerar imagens sintéticas realistas, SEDs e espectros para galáxias a partir de simulações de hidrodinâmica cosmológica.As observações simuladas levam em conta as diferentes populações estelares, os efeitos perturbadores do ISM empoeirado e a geometria 3D das galáxias, e podem ser imediatamente comparadas com dados observacionais. Apresentarei os resultados mais recentes sobre a comparação de dados sintéticos de diferentes simulações cosmológicas (EAGLE, TNG, Auriga, ARTEMIS…) com dados observacionais de comprimentos de onda UV a mm.Os tópicos a serem discutidos incluem a distribuição de energia espectral cósmica, funções de luminosidade multibanda, relações de escala de galáxias e índices de morfologia de galáxias para diferentes simulações cosmológicas. Também discutirei brevemente outras possibilidades e aplicações do código SKIRT, como transferência radiativa de raios X, transferência radiativa Lyman-alfa e transferência radiativa de linha não LTE.

Kinetic theory of vortex gases in low-dimensional superfluids
2024-07-04 11:00 - 13:00 | Online
To study strong turbulence in two-dimensional (2D) quantum gases, it must be taken into account the excitation of topological defects, the quantum vortices, and their dynamical interaction. The quantum vortices appear naturally in perturbed superfluids, particularly in atomic Bose-Einstein condensates (BECs). These structures are stationary solutions of the Gross-Pitaeskii equation (GPE), which is the equation that describes the evolution of quantum fluids, like BECs. Given that quantum vortices are a manifestation of quantum turbulence, a better understanding of turbulence could come from having a description of an ensemble of these excitations dynamically interacting. We start by going back to the GPE and study the dynamics of a single vortex, where we propose a correction to the vortex wavefunction that takes into consideration its motion in the BEC. With this correction, we are able to derive a vortex mass. Subsequently, we study the interaction of two vortices and obtain an interaction pairwise potential. Finally, we are in a position to focus on the Vlasov equation, from which we derive a kinetic model for a one species and two species vortex gas, encapsulating its statistical and dynamical features. We observe that the dispersion relation does not depend on the sign of the vortex gas, but only on its initial velocity and density, being constant when initialized with zero initial velocity or with an initial velocity perpendicular to the wave vector. This allows us to have a completely analytical kinetic description of strong quantum turbulence in low-dimensional quantum fluids.

Exploiting analogies between gravity and electrodynamics for numerical relativity
2024-07-04 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
General relativity and electrodynamics are both governed by systems of hyperbolic equations which need to satisfy a set of elliptic constraints throughout evolution. Approaches to solve numerically the Maxwell equations in the presence of charges has led to a variety of advantageous techniques developed over decades, such as particle-in-cell (N-body) simulations, unstructured meshes and machine-precision constraint-preserving discretizations. However, these and other techniques appear much more complicated to implement for numerical relativity. In this talk we will explore analogies between the Einstein and Maxwell systems that could allow numerical relativity to benefit from some of the techniques originally developed for numerical electrodynamics and plasma physics. These could also offer an alternative, yet intuitive, insight into spacetime dynamics. Finally, we will discuss some of the challenges that need to be overcome for an effective numerical implementation.

Absorption in the black hole ringdown
2024-07-11 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
In the last couple of years, we have made enormous progress in understanding how black holes “ring” — beyond linear order in perturbation theory. One effect currently under study is the absorption of black hole modes by the black hole horizon, which should cause the mode frequencies to evolve, as well as mode mixing. I will discuss the latest studies on this topic, and present some ongoing work looking for this effect in numerical simulations of black hole mergers.

Dynamics of magnetospheres of rotating compact objects with General Relativity
2024-07-16 09:30 - 11:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática)
Objetos compactos em rotação são conhecidos por alimentar os fenómenos astrofísicos extremos mais energéticos do universo. A sua rotação induz um campo elétrico exterior capaz de acelerar partículas eficientemente, povoando a magnetosfera com e± plasma através de processos de eletrodinâmica quântica (QED) e dando origem à radiação coerente e incoerente observada. Apenas é possível compreender estes fenómenos de primeiros princípios usando simulações cinéticas particle-in-cell (PIC) da magnetosfera global, capturando o fecho da corrente magnetosférica, processos QED, e relatividade geral (GR). Nesta Tese, generalizámos o código PIC avançado OSIRIS para coordenadas ortogonais curvilíneas arbitrárias, apropriadas a modelar a dinâmica dos plasmas em magnetosferas de objetos compactos, i.e. com curvatura do espaço-tempo significativa. A implementação detalhada nesta Tese estende a aplicabilidade desta ferramenta para lá de cenários astrofísicos. Em particular, para configurações laboratoriais em geometrias mais complicadas. Corremos simulações massivamente paralelas de magnetosferas de pulsares, executando experiências numéricas para compreender o papel da relatividade geral e fornecimento de plasma na fase de geração do feixe de rádio para rotadores de baixa obliquidade. Os resultados mostram que a GR é fundamental para o aparecimento do feixe radio em primeiro lugar para rotadores alinhados. Para estrelas mais velhas, pode até distinguir uma pulsar de uma estrela de neutrões. Nesta tese, explorámos ainda o efeito da GR quando a lacuna polar está em regime não-estacionária, caracterizada por ter uma lacuna (quase) em vácuo na base do conjunto de linhas de campo magnético abertas. Nestas condições, a descarga polar ocorre através de uma sucessão de filamentos de plasma isolados que não acompanham a rotação estelar, usualmente usados para explicar componentes derivantes do feixe. Os resultados demonstram o aparecimento de um novo filamento de plasma, dando uma explicação natural para a configuração de emissão núcleo mais bi-cone que concorda com as observações.

Em Direção às Redes de Sensores Quânticos
2024-07-26 09:00 - 11:00 | Online
Redes de sensores quânticos são uma estrutura para sensoriamento quântico distribuído. Em particular, elas visam caracterizar protocolos de sensoriamento onde cada uma das partes tem acesso a um parâmetro local, e em particular, a um canal local que codifica esse parâmetro sobre seus recursos quânticos. Neste projeto, começamos investigando a privacidade em tais protocolos, onde apenas a informação sobre uma função linear alvo dos parâmetros locais está disponível para cada parte. Como resultado, encontramos uma descrição completa dos estados que possuem essa propriedade, em termos da função alvo e da distribuição de recursos. Usando esses resultados, então procedemos para encontrar um conjunto de problemas que podem ser descritos por uma função linear de valores locais, que agora podem ser vistos como avaliações de um campo nas diferentes localizações. Usando isso, encontramos resultados de viabilidade e não-viabilidade sob os quais este problema converge para a solução correta, e, caso contrário, maneiras de encontrar o erro correspondente. Isso estará relacionado com as localizações dos sensores e o modelo do campo disponível. Ambos os trabalhos abrem um caminho para a implementação de uma rede de sensores quânticos.

Procura por sinais de nova física escondidos no Grande Colisor de Hadrões
2024-07-26 10:00 - 12:00 | Sala V0.15 (Piso 0 do Pavilhão de Civil) do IST
O Modelo Padrão (MP) da Física de Partículas é atualmente a melhor teoria para descrever a Natureza à escala subatómica. No entanto, apesar da sua notável concordância com os dados recolhidos até agora nos colisores, o SM deixa vários fenómenos por explicar. Têm sido efectuadas buscas de nova física no Grande Colisor de Hádrons (LHC) na tentativa de identificar uma versão mais completa do SM, mas esses esforços ainda não produziram o resultado desejado. Não podemos descartar a possibilidade de que as buscas de nova física sejam sinais perdidos cujas assinaturas experimentais são mais elusivas do que o esperado. Assim, nesta tese, estudamos sinais de nova física que podem estar escondidos nos dados do LHC, bem como extensões do SM onde esses sinais são previstos. Em particular, abordamos a produção de multibossões a partir de uma ressonância Z ′ pesada no quadro de um modelo de dupleto de dois-Higgs U(1)′ alargado próximo do mínimo (UN2HDM). Pequenos excessos em torno de 95 GeV observados em muitas pesquisas de um novo escalar em três canais de decaimento diferentes, γγ, τ τ e bb, motivam uma nova análise dos UN2HDMs. Neste contexto, verificamos quais as anomalias que podem ser explicadas por esses modelos, incluindo cenários em que os excessos num ou dois canais de decaimento acabam por ser flutuações estatísticas. O segundo objetivo desta tese é desenvolver ferramentas que possam tornar as pesquisas de nova física sensíveis a uma gama mais vasta de sinais, incluindo aqueles com assinaturas experimentais não convencionais. Para este fim, introduzimos o conceito de “Mass UnspeciTraduzido com a versão gratuita do tradutor - DeepL.com

Multi-Higgs e mais além: uma odisseia do vácuo às anomalias
2024-07-26 15:00 - 17:00 | Sala V0.15 (Piso 0 do Pavilhão de Civil) do IST
O Modelo Padrão da física de partículas descreve a estrutura da matéria e as interações fundamentais, cujo conteúdo ficou completo com a observação do bosão de Higgs em 2012, previsto exatamente há 60 anos. Contudo, o puzzle completo permanece por resolver existindo várias indicações de que física para além da teoria padrão é necessária. Nesta tese, exploramos extensões do sector escalar, uma das mais interessantes possibilidades de física para além do Modelo Padrão. Revemos extensões com um singleto extra (real ou complexo), um dubleto complexo ou um tripleto complexo.Extensões com tripletos escalares fornecem um interessante mecanismo para a explicação das massas dos neutrinos. Fazemos uma análise minuciosa da estabilidade do vácuo no modelo com apenas um tripleto complexo, ilustrando a possível ocorrência de mínimos não-físicos. Motivados por possíveis conexões com a violação da simetria carga-paridade no sector leptónico, também exploramos o espectro de massa do modelo com dois tripletos complexos.Se a simetria carga-paridade for quebrada de forma espontânea pelo vácuo, a existência de partículas mais leves do que o bosão de Higgs é inevitável. Considerando extensões com dubletos, construímos um modelo lepton-specific com quatro dubletos, no qual escalares podem ter decaimentos consideráveis para eletrões e muões, em contraste com os tipicos decaimentos leptónicos para taus.Finalmente, analisamos duas medições experimentais que continuam a desafiar uma explicação pelo Modelo Padr˜ao. O momento magnético anómalo do muão pode ser explicado no contexto de modelos com dois dubletos de Higgs, mas entra em desacordo com outros constrangimentos experimentais. Mostramos que adicionar leptões vector-like que não se misturam com os leptões do Modelo Padrão pode aliviar este problema.Contudo, surgem problemas com a perturbatividade de certos acoplamentos. De seguida, revisitamos uma das primeiras soluções propostas para as anomalias ATOMKI sob a forma de um novo bosão de gauge cuja carga é a diferença entre os números barifónico e leptónico. Elucidamos as suas várias desvantagens, mesmo após adicionar leptões vector-like.

Bias driven non-equilibrium phase transitions
2024-07-30 10:00 - 12:00 | Online
In this thesis, we investigated bias-driven non-equilibrium quantum phase transitions in a paradigmatic transport setup consisting of a quantum dot, with an interacting charging energy, connected to non-interacting leads. We mapped out the non-equilibrium zero-temperature phase diagram as a function of interaction strength and bias voltage across the dot.Our central results are the behavior of charge susceptibility and current noise near the phase transition. Specifically, we show that zero-frequency current fluctuations become critical and diverge as near the non-equilibrium critical points. The charge susceptibility also diverges at the transition.These results are achieved using a Random Phase Approximation (RPA). Additionally, we employ an Effective Stochastic Equation, developed by expanding the action to quadratic order in the fluctuations, which yields consistent results while offering a different physical interpretation.We validated our findings in the high voltage limit, where the system-leads interaction becomes Markovian, using the Lindblad master equation. At this limit, both the average current and current noise coincide with those of a non-interacting system, consistent with the RPA effective field theory.We used the Non-Crossing Approximation (NCA) to analyze the fermionic energy distribution beyond RPA despite its limitations in modeling the high-voltage regime. NCA predicts qualitative changes in the electronic distribution near the critical point, deviating substantially from Mean-Field predictions.Our research demonstrates that current noise is a valuable tool for detecting and probing critical fluctuations at quantum critical points. It also opens new pathways for studying other types of non-equilibrium voltage-driven transitions.

SEMANA DE ACOLHIMENTO DOS NOVOS ALUNOS DO MEFT 2024/2025
2024-09-05 10:30 - 12:00 | Anfiteatro GA5, Pavilhão Central
Sessões de Apresentação

SEMANA DE ACOLHIMENTO DOS NOVOS ALUNOS DA LEFT 2024/25
2024-09-05 14:30 - 16:15 | Anfiteatro PA1 (Piso -1 do Pavilhão de Matemática)

Variational quantum algorithms for many-body simulation and machine learning problems
2024-09-06 11:00 - 13:00 | Room 3.10 - Mathematics Building – 3rd floor
Near-term quantum simulators suffer from various imperfections. A key question is whether such noisy quantum devices can outperform classical computers. Several demonstrations for quantum advantage have been achieved for sampling problems in superconducting and optical platforms. While these proof of principle experiments show the superiority of quantum computers, they do not offer an immediate practical advantage due to the limited practicality of sampling problems. Variational quantum algorithms are the most promising approach for achieving practical quantum advantage. These algorithms benefit from a hybrid combination of quantum devices and classical optimizers. In this seminar, we show two distinct applications for such algorithms, namely: (i) quantum simulation of many-body systems; and (ii) machine learning problems. In the former, we show how symmetries can be harnessed in optimizing circuit design [1] and be implemented experimentally in superconducting quantum simulators [2]. For the latter, a novel error-mitigation algorithm is presented which significantly enhances the performance of variational quantum algorithms for supervised machine learning problems [3].

Modeling the strongfield dynamics of binary neutron star mergers
2024-09-12 14:30 - 16:00 | Physics Seminar Room - Physics Building - 2nd floor (2-8.3)
Binary neutron star mergers (BNSM) are associated to powerful gravitational and electromagnetic astronomical transients. Multimessenger observations of BNSMs promise to deliver unprecedented insights on fundamental physics questions, including constraints on dense matter models and the production of heavy elements. Detailed theoretical predictions of the merger dynamics are a crucial aspect for extracting information from such observations. This talk reviews recent progress in the modeling of BNSMs using simulations in 3+1 numerical general relativity. In the first part, I will discuss the first predictions for the complete (inspiral-merger-postmerger) gravitational-wave spectrum and their application in gravitational-wave astronomy. In the second part, I will discuss recent results on merger remnants and mass ejecta, the mechanisms behind kilonova light and their application to the analyses of astrophysical data.

Exotic Compact Objects with Reflecting Surfaces
2024-09-19 14:30 - 16:00 | Physics Seminar Room - Physics Building - 2nd floor (2-8.3)
We perform non-linear simulations of ultra-compact spacetimes with a light ring and an object with a surface that reflects scalar and/or gravitational fields.The object's material is unknown, but replaced by reflecting boundary, whose location can be freely chosen. We investigate the dependence of the emitted waveforms on the position of the surface and compare to the non-reflecting case. In the waveforms we are looking on features that are conjectured for some horizonless ultracompact objects, such as echoing signals and a cascade to higher multipoles

Quantum computing applied to extreme plasma physics
2024-09-30 11:00 - 13:00 | Pavilhão de Civil - Anfiteatro VA1
The main goal of this PhD project is to determine if and where Quantum Computing (QC) can offer an advantage over traditional (classical) methods when solving problems in Extreme Plasma Physics. This is a new and exciting research frontier, where open problems are abundant and well-defined directions are lacking. Quantum Computing, together with classical Machine Learning (ML), promise new insights into numerical modeling of physical systems, and will potentially work as "accelerators", that is, special-purpose software or devices to run part of a computation that would otherwise be unfeasible (both in memory and time) on ordinary algorithms and CPUs. Early results on current quantum computers and quantum simulators are still limited to toy-models or problems that can be easily run on classical HPC, but nevertheless they do show proof-of-concept and clear research directions. One of the goals of this PhD is to demonstrate "experimentally" on current quantum hardware simulations of simple plasms systems, with focus on Strong Field QED regime of interaction.

Semiclassical effects on the inner (Cauchy) horizon of rotating black holes
2024-10-03 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Semiclassical gravity leads to well-known important effects outside black holes such as the emission of quantum (Hawking) radiation. Recently, interesting semiclassical gravity effects inside black holes have also been unveiled. In this talk, we will present some of these effects, including the abrupt expansion, contraction and twisting that observers may experience when approaching the inner Cauchy horizon of rotating black holes (Kerr and Kerr-de Sitter), as well as the irregularity of this Cauchy horizon, with consequences for Penrose’s strong Cosmic Censorship hypothesis and the predictability of Einstein’s equations of General Relativity.

Relativistic dissipative fluids
2024-10-04 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
In general relativity we don't have any preferred time function, so we can not have infinite propagation speeds. Thus, parabolic systems like the Navier-Stokes equations are not possible. To overcome this several proposals for admissible theories have been put forward in the past. Notably, the first ones were ill posed, namely a small variation on the initial data produced huge differences on the solutions. Fortunately new proposals have arised which are well posed. Here we discuss one of them. In particular we shall concentrate on one describing conformally invariant fluids, the limit when the particle's mass is much smaller than their thermal speeds. In this case the universe of possible theories collapses to a four parameter family, Only one of them related to the propagation speeds of the system. This case is well posed. We shall further discuss some simulations exploring these free parameter variations and some efforts to construct algorithms to automatically generate computer codes for solving them.

Eyes on the invisible: Charting new horizons with the Event Horizon Telescope
2024-10-10 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The Event Horizon Telescope (EHT) collaboration has captured the first image of a black hole's event horizon in the galaxy M87, and subsequently, in the supermassive black hole at the center of our Milky Way, SgrA*. More recently, the collaboration has released the first follow-up image of M87*, utilizing observations from April 2018. The EHT has also revolutionized our understanding of the relativistic jets commonly present in active galactic nuclei, revealing the processes governing the jet formation, collimation and acceleration with an unprecedented angular resolution. The upcoming next-generation Event Horizon Telescope (ngEHT) is poised to significantly upgrade the current system by adding new stations and introducing multi-frequency observational capabilities. These will notably improve the ngEHT's angular resolution, dynamic range, and overall coverage. This expansion is crucial for enabling the ngEHT to create the first movies of black holes, a leap forward in understanding the processes of black hole accretion and the formation of relativistic jets. In addition, the ngEHT's advanced features will be instrumental in exploring alternative theories to General Relativity and will expand our observational reach to include potentially a dozen new black holes. By adding an orbiting antenna, the Black Hole Explorer (BHEX), a potential NASA mission, will discover and measure the bright and narrow “photon ring” that is predicted to exist in images of black holes, and fully encodes the space-time metric

Ion-implanted gallium oxide for small-field beam dosimetry
2024-10-11 10:30 - 12:00 | Online
Monoclinic -Ga₂O₃ has been attracting renewed interest due to its compelling properties such as its wide bandgap (~4.8 eV at room temperature) and high breakdown electric field (~8 MV/cm), which make it suitable for multiple applications, ranging from gas detectors to power electronics. In the case of optical applications, because of its high transparency, many different optical centres may be exploited, with emissions spanning the spectral region from the ultraviolet down to the near-infrared. For instance, the Cr3+ red/nearinfrared emission in -Ga₂O₃ has been studied for its potential for ionising radiation detection in the context of optical in-vivo dosimetry. Moreover, thanks to the (100) easy-cleavage plane, it is possible to produce thin flakes by conventional mechanical exfoliation approaches, such as the scotch tape method; in spite of being useful for fast prototyping, these techniques lack reproducibility and control. Recently, we developed an innovative process for the fabrication of single-crystalline -Ga₂O₃ microtubes and nanomembranes based on ion implantation. Additionally, this process allows the tailoring of their opto-electrical properties in the same step, thus contributing to its scalability for future industrial applications. In this context, this project aims at establishing a doping and strain engineering strategy to produce and to tune the properties of -Ga₂O₃ nanomembranes for applications in small-field beam dosimetry. The fundamental physical processes underlying this innovative processing technology are currently under investigation by applying a powerful combination of experimental material characterisation and computational techniques, including Rutherford Backscattering Spectrometry and X-ray Diffraction, as well as Molecular Dynamics simulations. The produced membranes will then be used to develop radiation detectors, to be tested and characterised as active and/or passive dosimeters for smallfield beam

The effect of resummation on retarded Green's function and greybody factor in AdS black holes
2024-10-17 14:30 - 16:00 | Sala de seminários do DF (2-8.3), 2º piso do Pavilhão de Física
The study of linear scalar perturbations in AdS_5 black holes typically reduces to the analysis of ODEs of the Heun type. Recently, the connection coefficients of the Heun equation have been computed in terms of the Nekrasov-Shatashvili (NS) free energy of an SU(2) supersymmetric gauge theory with four fundamental hypermultiplets. Using the exact form of these connection coefficients and summing over the instanton contributions of the NS function, we present asymptotic expansions in the small horizon limit for the retarded Green's function and the greybody factor in asymptotically AdS black holes. This talk is based on joint work with Shankhadeep Chakrabortty and Arpit Maurya.

Monte Carlo study of charged-particle collisions in low-temperature plasmas
2024-10-17 16:00 - 18:00 | Online
Charged-particle (Coulomb) collisions are often neglected when studying low-temperature plasmas, due to their low ionization degrees ∼ 10⁻⁷-10⁻³. However, Coulomb collisions are known to significantly alter the electron kinetics in various gases, above ionization degrees ∼ 10⁻⁶-10⁻⁵. This work examines the effect of charged-particle interactions on the electron kinetics of low-temperature plasmas, implementing electron-electron and electron-ion collisions in the open-source LoKI-MC code. This numerical tool simulates the classical motion of numerous electrons, interrupted by collisions with neutrals, using the Monte Carlo method. Several techniques are employed to describe Coulomb collisions, with results being compared to theory and other modelling tools. Nanbu's method is argued as the most computationally efficient and accurate approach for Monte Carlo simulation of Coulomb collisions. The effects of electron-electron and electron-ion collisions are then extensively studied and documented for various gases, ionization degrees, and a wide range of DC electric fields. This includes the analysis of the electron energy distribution functions, transport coefficients, the phenomenon of negative differential conductivity and perturbations to Coulomb collision theory caused by electron-neutral collisions. The impact of Coulomb collisions is also accessed on time-dependent electron kinetics subject to a model nanosecond electric-field pulse. In particular, electron-electron collisions are shown to facilitate energy relaxation to neutrals. Finally, an adjacent study on improvements to the Monte Carlo method is presented, which enables significant computational gains in the simulation of electron-neutral collisions.

Exploring the hydrogen color spectrum: focus on green hydrogen production and applications
2024-10-22 14:00 - 16:00 | Seminar Room - Physics Building - 2nd floor
Transitioning to the hydrogen economy is essential to reduce greenhouse gas emissions and addressthe challenges of climate change. This presentation analyses the various hydrogen productionmethods, typically classified as hydrogen colors, that reflect the source, the technology, and thecarbon emissions associated with each method. Although this "hydrogen color spectrum" includesgrey, blue, and turquoise hydrogen, the focus is on green hydrogen, produced through waterelectrolysis powered by renewable energy sources such as wind and solar.We will discuss the role of electrolyzers in splitting water into hydrogen and oxygen, presenting thecommercially available types. We will also emphasize the growing importance of green hydrogen indecarbonizing sectors that are hard to electrify, such as heavy industry and mobility, and presentseveral applications.

Instrumentation, control and monitoring of superheated liquid detectors for detection of nuclear materials at the Portuguese Research Reactor
2024-10-23 09:00 - 11:00 | Online
Nuclear and radioactive materials see regular use in our daily lives. Whether associated with energy production, research or medical applications, there are more and more nuclear materials in circulation across the world, making their control and detection necessary to ensure the health and safety of the population. However, the loss of these materials is not as uncommon as one would expect. Ranging from improper disposal to incidents related with other malicious uses, the reasons for the loss of these materials mostly range from the inability of current detectors to be able to detect shielded radiation sources.This thesis investigates the usage of superheated liquid detectors as a way to detect shielded radiation sources. This was achieved through shielding different radiation sources with different attenuating materials commonly used in scenarios of smuggled radioactive materials. The Superheated Detectors are coupled to an acoustic instrumentation system previously used by the SIMPLE project in search of dark matter as well to an optical instrumentation system capable of identifying nucleation events through a machine learning algorithm. The inclusion of this optical system allowed to corroborate the data obtained from the acoustic system, being able to currently measure and detect observed events within the detector gel with a precision rate of 81.25%, thus improving the efficiency of these devices, allowing for the detection of shielded sources.

Relativistic Navier-Stokes: recent developments
2024-10-24 14:30 - 16:00 | Sala de seminários do DF (2-8.3), 2º piso do Pavilhão de Física
The Navier-Stokes equations are ubiquitous in the physical description of our universe, but their relativistic counterpart, as originally formulated many decades ago, suffer severe issues. In recent years, a well-behaved version of relativistic Navier-Stokes has been proposed, satisfying good properties of well-posedness and causality. Alternative formulations, like the widely used Muller-Israel-Stewart (MIS) theories that successfully describe the quark-gluon plasma, are known to present limitations. Moreover, weak processes in neutron star mergers are believed to give rise to an effective viscosity, for which MIS descriptions find similar limitations. We present recent developments in numerical evolutions of the relativistic Navier-Stokes equations, pointing to the description of these systems, as a promising approach for which these limitations are absent.

New post-Newtonian results for compact binaries in general relativity and scalar-tensor theories
2024-10-31 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In the first part of my talk, I give on overview of some recent results concerning the two-body problem in general relativity at high post-Newtonian (PN) order. I will present the energy flux at 4.5PN order, the equations of motion at 4.5PN order, and the memory contributions to the 3.5PN order waveform. In particular, I will discuss some subtleties about the definition of the center-of-mass frame, and its relevance to the comparison with second-order self-force (2SF) results. In the second part of my talk, I will discuss recent work on compact binaries on eccentric orbits in scalar-tensor theory. I will discuss how I obtain the quasi-Keplerian motion at 2PN and the fluxes of energy and angular momentum at 1.5PN (i.e. 2.5PN beyond the leading dipolar radiation), which finally lead to the secular evolution of the orbital elements (this is the main prediction for GW observations, namely the "chirp"). I discuss subtleties in the treatment of hereditary terms (such as the tails and the memory), and highlight the usefulness of studying these theories to better understand general relativity.

Amide-Functionalized/BODIPY MOFs: Unveiling New Frontiersin Catalysis, Wastewater Treatment, and Energy Conversion
2024-11-05 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Functionalized metal-organic frameworks (MOFs) and coordination polymers (CPs) are emergingas attractive materials for a variety of significant applications, such as gas adsorption,wastewater treatment, catalysis, and sensing. The incorporation of functional groups likeamides and BODIPY units significantly enhances these materials’ properties, leading toincreased stability, improved electronic conductivity, and a greater number of active reactionsites. These functionalized materials’ applications in energy conversion, pollutant removal, andcatalysis demonstrate their crucial role in making processes more efficient and sustainable. Thistalk will showcase how amide- and BODIPY-functionalized MOFs/CPs are helping address energyand environmental challenges.

Structuring light with optical metasurfaces
2024-11-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Metasurfaces are planar metamaterials consisting of nanostructures that allow to manipulate the phase, amplitude and polarization of light on a subwavelength scale with unprecedented control, representing the state-of-the-art in structured light. This nanotechnology is not anymore, an academic curiosity: today metasurfaces are being mass produced and can be fabricated with large areas (10 cm) using advanced lithography techniques. These meta-optics are pushing the boundaries of structured light, allowing to exploit all of its degrees of freedom, even creating correlations between these resulting in complex multimodal forms of light, such as space-time beams. In this contribution we will discuss the most recent advances in the field and where the most exciting opportunities lie ahead, in particular in the areas of nonlinear optical neural networks and structured laser-matter interactions.

An overview of the asymptotics of a scalar field near spatial infinity
2024-11-07 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Conformal geometry tools allow us to study global geometric aspects of a spacetime using local differential geometry. In the context of my talk, I will focus on a particular conformal representation of Minkowski spacetime which allows us to study the asymptotics of massless fields near spatial infinity. I will briefly discuss the analysis of the asymptotics of the wave equation in the context of this conformal representation and its application in the calculation of asymptotic conserved quantities associated with this field.

GWDALI: Derivative approximation for gravitational wave likelihoods
2024-11-13 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
In the next decade, third-generation gravitational wave (GW) observatories, such as the Einstein Telescope and Cosmic Explorer, will begin operation, enabling the detection of compact object coalescences at unprecedented distances (up to z < 100). Analyzing these sources cosmologically necessitates GW parameter inference, which typically involves around 15 parameters for each detection—a process that is computationally intensive. To address this challenge, we discuss the application of Derivative Approximation for Likelihoods (DALI) in gravitational wave and cosmological data analysis. DALI is a more time-efficient approach that incorporates higher-order terms in the Taylor expansion of likelihoods, which is particularly advantageous when the expected posterior distributions deviate from Gaussianity, rendering the Fisher Matrix approximation unreliable. Such deviations often occur in the context of GW signals from compact binary coalescences, especially in cases of parameter degeneracies, such as the distance-inclination degeneracy. In this presentation, we explore the behavior of gravitational wave DALI-posteriors under various parameterizations of GW signals and demonstrate how their accuracy can be enhanced using automatic differentiation (autodiff).

Modeling of atomic oxygen in the effluent of a CO2 microwave discharge
2024-11-15 09:00 - 11:00 | Online
This study examines the kinetics of low-pressure 2.45 GHz microwave COâ‚‚ plasmas under conditions aimed at optimizing COâ‚‚ dissociation for energy-efficient gas reforming-based applications on Earth and Mars. It focuses on the behavior of ground-state atomic oxygen, O(Â³P). The LisbOn KInetics (LoKI) framework composed of a Boltzmann solver (LoKI-B) and chemistry solver (LoKI-C), modified to include extensions for the vibrational sets of COâ‚‚ and CO; and the excited state O(Â¹S), was used to describe electron kinetics, heavy-species interactions, and surface recombination in both plasma and post-discharge regions.The modeling study developed capitalizes on recent experimental data with operating parameters varied as follows: pressures of 120-500 Pa, absorbed powers of 600-1200 W, and flow rates of 74-370 sccm. Results align well with experimental data on temperature and conversion, though discrepancies remain, particularly with the highest dissociation of 90.3%.While attempting to describe the experimental data, various potential sources for the O(Â³P) concentration peak observed in the post-discharge were explored, including the vibrational dissociation of COâ‚‚, Oâ‚‚, and CO, and reactions with electronically excited species. However, simulations indicate that most highly excited vibrational and electronic states are depleted early in the post-discharge. Thermal contraction was inspected for its role in the increase of O(Â³P) concentration. Simulations reproduced the peak this way, although with some differences in shape and position. Findings suggest that this thermal contraction results from non-uniform cooling, not collisional mechanisms driven by excited states. O(Â³P) destruction was analyzed by parametric studies on oxygen recombination mechanisms, especially at the reactor walls.

Assessing Quantum Computers' Performance in the NISQ Era
2024-11-15 14:00 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1
Dinâmicas quânticas em ambientes externos sofrem de decoerência e dissipação, as principais fontes de erro nos processadores quânticos atuais. A degradação da fidelidade de um estado quântico — medida da correlação entre os estados ideal e imperfeito — caracteriza a degradação inevitável nesses processos. Compreender como essa degradação varia conforme a natureza e severidade dos erros é essencial para entender a decoerência e melhorar algoritmos. No entanto, a média da fidelidade ignora aspectos dinâmicos importantes, que esta tese visa abordar. Na primeira parte, analisamos a degradação da fidelidade em circuitos quânticos aleatórios, considerando erros decorrentes de implementações imperfeitas de portas quânticas de dois qubits e permutações de qubits. Mostramos que a fidelidade decai exponencialmente tanto com a profundidade do circuito quanto com o número de qubits elevado a uma potência dependente da arquitetura e estimamos as taxas de degradação com base na amplitude dos erros. Estes resultados auxiliam na avaliação de computadores quânticos por meio do Volume Quântico — uma métrica para processadores — e indicam estratégias de otimização. Na segunda parte, exploramos o impacto da dissipação em dinâmicas caóticas e regulares. Constatamos que a média da fidelidade não diferencia estes sistemas, então analisamos as propriedades espectrais dos mapas dissipativos. Examinando várias dinâmicas regulares, observamos que certas características espectrais persistem até um limite de dissipação, permitindo distinguir dinâmicas regulares de caóticas. Esta tese caracteriza a acumulação de erros em circuitos quânticos e ajuda a compreender a influência do ruído em canais quânticos caóticos e regulares.

Emergent Topology in Many-Body Dissipative Quantum Matter
2024-11-16 10:00 - 12:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
The identification, description, and classification of topological features is an engine of discovery and innovation in several fields of physics. This research encompasses a broad variety of systems, from the integer and fractional Chern insulators in condensed matter, to protected states in complex photonic lattices in optics, and the structure of the QCD vacuum. Here, we introduce another playground for topology: the dissipative dynamics of pseudo-Hermitian many-body quantum systems. For that purpose, we study two different systems, the dissipative Sachdev-Ye-Kitaev (SYK) model, and a quantum chaotic dephasing spin chain. For the two different many-body models, we find the same topological features for a wide range of parameters suggesting that they are universal. In the SYK model, we identify four universality classes, related to pseudo-Hermiticity, characterized by a rectangular block representation of the vectorized Liouvillian that is directly related to the existence of an anomalous trace of the unitary operator implementing fermionic exchange. As a consequence of this rectangularization, we identify a topological index $\nu$ that only depends on symmetry. Another distinct consequence of the rectangularization is the observation, for any coupling to the bath, of purely real topological modes in the Liouvillian. The level statistics of these real modes agree with that of the corresponding random matrix ensemble and therefore can be employed to characterize the four topological symmetry classes. In the limit of weak coupling to the bath, topological modes govern the approach to equilibrium, which may enable a direct path for experimental confirmation of topology in dissipative many-body quantum chaotic systems. *A. M. García-García, L. Sá, J. J. M. Verbaarschot, and C. Yin, arXiv:2311.14640 (2023)

Exotic hadrons with heavy quarks
2024-11-19 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
For several decades, the quark model suggested 60 years ago as a classification scheme for multiquark states had been a powerful and successful tool to understand and predict properties of hadronic states in QCD. However, since 2003, when the Belle Collaboration discovered the X(3872), an enigmatic state in the spectrum of charmonium with the properties at odds with the predictions of the quark model, a new era in the spectroscopy of hadrons containing heavy quarks began. Since then, many new states in the spectrum of charmonium and bottomonium have been discovered that do not fit into the quark model scheme and qualify as exotic states. Most of them reside near strong open-flavour thresholds that leave imprint on their nature and properties. I will discuss how one can extract the information contained in the experimental data on exotic hadrons with heavy quarks and employ this information to make predictions for not yet observed hadrons and their properties.

How does the brain control the eye movements ? An analysis-by-synthesis approach
2024-11-19 15:00 - 17:00 | Sala V0.08, Piso 0 - Pavilhão de Civil
Apesar de extensa pesquisa, os mecanismos subjacentes ao controlo dos movimentos oculares pelo cérebro ainda não são bem compreendidos. Modelos biomiméticos de sistemas biológicos têm fornecido informações valiosas sobre o seu funcionamento e controlo. Este trabalho tem como objectivo desenvolver um modelo artificial do sistema ocular humano para explorar como o cérebro controla movimentos sacádicos.O controlo de movimento sacádico é formulado como decorrente de um processo de optimização aplicado aos sinais de controlo, onde métricas como precisão, duração, energia e tensão são usadas para avaliar o desempenho do movimento resultante. Deste modo, um algoritmo model-free baseado em aprendizagem por reforço é utilizando para aprender, através de tentativa e erro, como controlar um sistema em malha-aberta, utilizando sinais de controlo inspirados em argumentos biológicos.Um modelo computacional realista do sistema ocular humano, com seis graus de liberdade, é utilizado para analisar como diferentes sinais de controlo afetam o movimento ocular resultante. Os resultados obtidos através desta metodologia demonstram que os controlos aprendidos replicam características de sacadas semelhantes às humanas, tais como as relações de main sequence, a conformidade com a lei de Listing, e o acoplamento antagonista entre os músculos extraoculares - sem que esses comportamentos sejam impostos diretamente. Adicionalmente, esta metodologia foi utilizada para analisar o impacto dos factores presentes na função de recompensa, bem como a introdução de ruído dependente do sinal e aditivo, nas estratégias de controlo sacádico e nos movimentos resultantes.

Design of polyurethane-based membranes for a novel generation of artificial respiration devices
2024-11-20 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Extracorporeal Membrane Oxygenation (ECMO) is a life-saving intervention for severe respiratory and cardiac failures, relying on a membrane blood oxygenator (MBO) as its main component. Current MBOs require large membrane surface areas with adequate hemocompatibility, otherwise coagulation issues will arise. Despite technological progress, there is currently no MBO that supports prolonged ECMO efficiently. This contribution discusses previous research by the Membrane, Chemical, and Electrochemical Processes Group (MemChem) of the Center for Physics and Engineering of Advanced Materials (CeFEMA) on the production of polyurethane-based membranes. Ongoing and future research carried out within the scope of the Biomimetic Membranes for Organ Support (BioMembrOS) project will also be presented, where we are developing new polyurethane-based membranes that combine improved oxygen and carbon dioxide permeabilities with enhanced hemocompatibility, mechanical strength, and durability.

Breaking Buchdahl: Ultracompact stars in semiclassical gravity
2024-11-21 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The Buchdahl theorem imposes a bound on the maximum compactness that stars in equilibrium can achieve in general relativity. This bound is one of the theoretical motivations behind the belief that the dark and compact objects that we observe must correspond to black holes. In this talk, I will revise the hypotheses behind the Buchdahl theorem and address the consequences of individually relaxing its assumptions.In particular, if the energy density of the stellar fluid is allowed to become negative, it is possible to obtain regular stars as compact as black holes. To conclude, I will show how similar models of black hole mimickers are found within semiclassical theories of gravity that consider the backreaction effects of the quantum vacuum.

Training optical neural networks for nonlinear logics: Towards analog simulators of artificial life
2024-11-21 15:00 - 17:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)/Online
Esta pesquisa investiga o potencial de sistemas óticos para realizar cálculos não lineares usando a luz, um meio inerentemente linear. Ao introduzir não linearidade numa rede neuronal física, exploramos o ajuste de várias camadas e elementos óticos de forma a identificar a arquitetura ideal para o problema em questão. A fase inicial envolve modelar materiais não lineares e analisar as suas propriedades na integração no sistema. Como problema inicial, implementamos um decodificador ótico e uma porta lógica AND ótica, utilizando feixes de Laguerre-Gaussian com diferentes momentos orbito-angulares para codificar os estados binários possíveis nestes sistemas. As máscaras de fase são otimizadas com um algoritmo baseado no teorema adjunto, que encontra o design ótimo através da correspondência de frentes de onda. Isto permite que múltiplos feixes de entrada distintos interajam e produzam os vários modos de saídas desejadas com base nas regras de mapeamento predefinidas. Para aumentar o desempenho do sistema, a otimização é conduzida no espaço de Fourier. De forma a otimizar tarefas cada vez mais complexas, desenvolvemos também um modelo de aprendizagem em paralelo mais eficiente no treino, que através do método do máximo declive descobre a arquitetura ideal para as propriedades contínuas dos componentes óticos utilizados no sistema. Os resultados desta pesquisa confirmam a viabilidade de treinar redes neurais óticas para cálculos não lineares, além de aprimorar a manipulação de luz coerente.Além das portas lógicas óticas simples, esta abordagem estende-se à simulação de uma forma de vida artificial. Automatos celulares, normalmente criados a partir de conjuntos de regras simples, são realizados opticamente. Investigamos a capacidade do sistema de caracterizar várias regras de atualização de estado, estabelecendo as bases para futuras aplicações, como a produção ótica do sistema Lenia — um modelo de autômato celular contínuo a duas dimensões. Estes avanços oferecem uma base não apenas para a evolução da computação ótica, mas também de um novo modelo para explorar vida artificial e autômatos celulares em sistemas físicos ressonantes.

Skin-Inspired Magnetoresistive-based Tactile Sensor for Force Characterization in Distributed Areas
2024-11-26 09:00 - 11:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
O tacto é um sentido indispensável para os organismos mais avançados, em particular para o ser humano, pois fornece informações relativas à forma, dimensões, temperatura e textura do que nos rodeia. Na robótica e automação, a integração de sensores tácteis tem-se tornado cada vez mais relevante, permitindo que os dispositivos interajam adequadamente com o meio envolvente. Este estudo teve como objetivo desenvolver um dispositivo biomimético, inspirado na pele, capaz de detetar uma força aplicada, caracterizá-la em três dimensões e determinar o ponto de aplicação.O dispositivo foi concebido como uma matriz 4x4 de sensores magnetorresistivos, wire-bonded a uma PCB e encapsulados em epoxy. Estes sensores detetam o campo magnético gerado por um elastómero magnetoreológico sobreposto, composto por Ecoflex e partículas ferromagnéticas de neodímio-ferro-boro de 5 μm. Testes de integridade estrutural demonstraram que o dispositivo suporta forças superiores a 100 N, quando cobertos por 0,12 mL de epoxy por chip.Uma plataforma de movimento tridimensional equipada com uma ponta de indentação e um sensor de força foi utilizada para recolher dados do dispositivo, utilizados posteriormente para treinar redes neuronais, capazes de prever as características da força aplicada. O modelo de deteção de magnitude foi treinado com 31260 pontos de dados, conseguindo caracterizar a força com um erro absoluto médio entre 0,07 e 0,17 N. O modelo de sensibilidade espacial foi treinado com 171008 pontos e previu a localização da pressão aplicada com um erro absoluto médio de 0,26 mm e 0,63 mm para pontos fora da área de teste.

Magnetoresistive devices for industrial applications: improvement of thermal robustness
2024-11-26 11:00 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Este estudo optimiza as junções magnéticas de efeito túnel para aplicações industriais que requerem uma elevada estabilidade térmica e uma resposta linear. Concentrando-nos em antiferromagnetos sintéticos (SAFs) com MnNi para fixação inferior e MnIr para fixação suave, determinámos que 0.65 nm é a espessura do espaçador não magnético de Ru que maximiza a linearização, evidenciada por \textit{plateaus} mais largos nas medições VSM. Os sensores TMR fabricados com uma espessura de CoFeB na camada livre de 2,4 nm produziram um rácio TMR com um pico de 35,5%, que, após recozimento cruzado a 330ºC (2h) e 165ºC (1h) e arrefecimento num campo magnético de 1 T, apresentou 64,5% TMR à temperatura ambiente, diminuindo gradualmente para 47% a 150ºC. No entanto, a linearidade foi perdida a 175ºC, uma vez que as curvas VSM se assemelhavam a amostras recozidas a 180ºC, ambas superiores à segunda temperatura de recozimento. Uma exploração da integração dos sensores numa ponte de Wheatstone mostrou uma sensibilidade melhorada em [mV/V]/Oe com uma saída bipolar de -V a +V, confirmando o potencial das SAFs à base de MnNi para aplicações de deteção estáveis e de elevado desempenho sob stress térmico.

Modeling and Optimization of Multi-Level Magnetic Tunnel Junctions for Nanoelectronic Applications
2024-11-26 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Esta tese de mestrado investiga o design, a fabricação, a simulação e a caracterização de dispositivos MTJ (Magnetic Tunnel Junction, Junção de Tunelamento Magnético) de múltiplos níveis, com o objetivo de otimizar o seu comportamento de mudança de estado magnético para aplicações em circuitos de memória e lógica. Foram fabricados dispositivos MTJ incorporando tanto elipses únicas quanto duas elipses cruzadas (TCE, Two-Crossed Ellipses) como a camada livre foram fabricados e testados para examinar como a geometria da camada e a configuração do dispositivo afetam a estabilidade dos estados pretendidos. Foram realizadas medições de magnetorresistência e efeito Hall planar (PHE, Planar Hall Effect) para caracterizar o comportamento do dispositivo sob condições de campo variadas. As medições de magnetorresistência revelaram-se inválidas na obtenção de configurações de múltiplos estados estáveis, enquanto as medições de PHE demonstraram respostas mais consistentes.Para complementar o trabalho experimental, foi desenvolvido um modelo teórico para simular o comportamento magnético destes dispositivos. O modelo inclui alguns ajustes dependentes do ângulo para a energia de desmagnetização, aproximando-se dos resultados obtidos através do Mumax3. Apesar das limitações iniciais, o modelo consegue capturar os aspetos fundamentais do comportamento magnético, fornecendo uma boa base para futuras otimizações. A falta de passos de metrologia ao longo da fabricação limitou a deteção de possíveis defeitos, o que destaca a importância de verificações regulares com estruturas de teste na própria sample para o futuro. Além disso, mais simulações das respostas de PHE e correntes de alteração de estado seriam benéficas, alinhando-se com o esforço futuro para implementar estes dispositivos em redes para aplicações em nanoeletrónica.

Revisiting magnetic tape readout using TMR sensors
2024-11-26 15:30 - 17:30 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Durante quase um século, fitas magnéticas (de áudio) têm preservado informações de valor inestimável, desde transmissões históricas até músicas intemporais, capturando uma parte significativa do nosso património cultural. Com o passar do tempo, as fitas têm vindo a deteriorar-se e a sofrer diversos tipos de danos, levando à perda de informações valiosas. É crucial desenvolver métodos para digitalizar estas fitas danificadas sem causar mais danos. Os sensores TMR (magnetoresistivos de efeito de túnel), combinados com um equipamento personalizado, são ideais para esta aplicação devido à sua alta sensibilidade, operação à temperatura ambiente e resolução espacial micrométrica.Para modelar o campo magnético das fitas, foram realizadas simulações usando a metodologia dos elementos finitos e análise analítica. Foram desenvolvidas várias versões das sondas (com diferentes configurações de sensores) para verificar a precisão do equipamento, otimizar o processo de integração do sensor ao PCB e aplicar as conclusões obtidas nas simulações. Todas as medições foram realizadas usando hardware e software personalizados. A evolução entre as versões proporcionou resultados promissores e melhorias, destacando os pontos mais importantes necessários para o progresso em futuras iterações.

MXenes: energy conversion and storage applications
2024-11-27 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Low-cost non-noble metal electrocatalysts are currently the focus of research and development for energy conversion and storage devices. MXenes, the newest class of two-dimensional materials, first reported in 2011, have high surface area, nanometer layer thickness, hydrophilicity and high electrical conductivity that favor their performance for electrocatalytic reactions. We will introduce niobium carbide MXene obtained from its MAX phase by chemical synthesis and characterized regarding its morphology, structure and electrochemical activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) as well as for charge storage in different electrolytic media. To further enhance its performance for use in energy storage devices, heteroatoms can be inserted to adjust the interlayer structure

Liouvillian Tomography in Noisy Intermediate-scale Quantum Computers
2024-11-27 16:00 - 18:00 | Online
Nas últimas quatro décadas, foram propostas várias aplicações entusiasmantespara a computação quântica. Contudo, os computadores quânticos atuais, apelidados de computadores Noisy Intermediate-Scale Quantum (NISQ), estão substancialmente limitados devido a portas quânticas imperfeitas e a interações com o meio envolvente. Para avaliar o papel destes fatores na dinâmica de qubits, a tomografia de Liouvillianos foi proposta como um método de estimar o gerador de evoluções Markovianas. Neste trabalho, propomos um novo protocolo de tomografia de Liouvillianos que elimina a hipótese Markoviana ao considerar um problema de regressão sobre derivadas de distribuições de probabilidade.Adicionalmente, apresentamos dois algoritmos para tomografia de processos e tomografiaauto-consistente de estado e medida (SPAM). Os três protocolos tomográficos são testados com dados simulados para sistemas de 1, 2 e 3 qubits. Tanto tomografia de processos como de SPAM mostraram-se capazes de produzir estimativas de alta \textit{fidelity} que possibilitam a sucessiva aplicação de tomografia de Liouvillianos. Os Liouvillianos estimados reproduziram os valores previstos ao nível do Hamiltoniano, taxas dissipativas e espectro. Pelo contrário, os operadores de salto mostraram-se mais suscetíveis a erros, resultando em estimativas com desvios significativos dos valores previstos. Por fim, tomografia de Liouvillianos foi aplicada a circuitos de dois qubits no computador quântico Helmi, para obter o gerador da dinâmica resultante quando nenhuma operação é aplicada sobre os qubits.Apesar de algumas limitações, acreditamos que este trabalho constitui um avanço no campo de tomografia de Liouvillianos ao propôr o primeiro protocolo capaz de capturar dinâmica não-Markoviana.

Improving the vacuum baseline for in-medium jet physics studies
2024-11-27 17:00 - 19:00 | Online/Password: [REDACTED]
Os esforçoes teóricos das últimas decadas, em conjunto com o aumento gradual de energia disponível em colisionadores de iões pesados, levaram à descoberta do Plasma de Quarks e Gluões (QGP), um meio partónico com um curto tempo de vida e que se comporta como um liquido quente de baixa viscosidade.Devido ao seu curto tempo de vida, o seu estudo é baseado em comparações entre colisões de protão-protão e iões pesados, pelo que a precisão protão-protão é crucial.Jatos --- chuveiros colimados de partículas --- são modificados ao atravessar este meio e podem ser usados para estudar a sua dinâmica. Este trabalho investigou as modificações na subestrutura de jatos, resultantes de uma referência de protão-protão melhorada, cujo elemento de matrix contém correções de primeira ordem (NLO). Um estudo di-jato protão-protão foi feito no regimo cinemático de ALICE, simulando as modifições do meio com modelos baseados numa confiuração de antena, por forma a estimar os efeitos de coerência. Duas análises foram feitas, uma em ordem fixa com o programa MADGRAPH, em que os modelos de meio foram aplicados diretamente à configuração do elemento de matrix em NLO e outra considerando o chuveiro completo, onde a simulação do evento foi feita com PYTHIA e o elemento de matrix NLO com POWHEG.Os resultados estão de acordo com os dados de ALICE, quando se considera o chuveiro completo e sugerem que parte das modificações de jatos podem ser explicadas sem um efeito de alargamento da antena.Isto verificou-se para ambas as referências e usando dois algoritmos de chuveiro, VINCIA e o algoritmo padrão de PYTHIA.

Searching for Beyond the Standard Model particles decaying to muon pairs with SND@LHC
2024-11-28 08:30 - 10:30 | Online
Apesar do Modelo Padrão (MP) ser uma teoria muito bem sucedida, não é suficiente para explicar todos os problemas da física moderna. Para estes,é necessário extender o MP com recurso a física para além do modelo padrão (BSM). O Scattering and Neutrino Detector at the LHC (SND@LHC) é uma experiência compacta e autónoma cujo objetivo principal é a observação de neutrinos de colisor. Nesta tese, realizamos o primeiro estudo de Feebly Interacting Particles (FIPs) em SND@LHC.Esta análise foca-se mais na assinatura experimental do decaimento escolhido (para dimuão) do que na partícula que decai, em busca de independência do modelo de FIP. O modelo de referência escolhido foi o Higgs Escuro, um escalar cuja interação com as partículas do MP se faz através de mistura com o bosão de Higgs do MP. Esta FIP foi simulada utilizando o Forward Experiment Sensitivity Estimator (FORESEE), com uma massa de 251.2MeV e a decair no alvo do detetor. A simulação foi posteriormente convertida para um formato compatível com SNDSW. Com recurso a amostras de simulação de Monte-Carlo do ruído e de dados experimentais, foram implementados vários cortes de seleção , resultando num ruido de neutrinos de <0.2 eventos em , numa estimativa de ruído na zona de sinal de em para as melhores condições do detetor, correspondendo a 7 eventos necessários para a rejeição de apenas ruído a 5 sigma, e simultaneamente retendo 12.78% de eficiência de seleção do sinal. Combinando estes valores, poderíamos esperar rejeição de apenas ruído após, em média, 54 decaimentos de Higgs Escuros no alvo do detetor. Foram também excluídos ângulos de mistura do Higgs escuro superiores a para a massa estudada.

DeepPlanner4Cardio: An automatic multi-view planning tool for Cardiac MRI
2024-11-28 10:30 - 12:30 | DF Seminar Room (2-8.3), 2nd floor of Physics Building/Online (Password: [REDACTED]
Cardiac magnetic resonance imaging (Cardiac MRI) is an ionizing radiation-free medical imaging technology used to monitor the function and structure of the cardiovascular system. Its disadvantage is that it’s a lengthy exam, demanding high levels of patient cooperation, and can take up to an hour, depending on the operator’s skill. A time-consuming element is the planning of the four standard cardiac views (2-chamber, 3-chamber, 4-chamber, short axis) needed for obtaining cardiac volumes and other measurements essential for a precise diagnosis. As cardiovascular diseases (CVDs) are the leading cause of death globally, simplifying and automating parts of the Cardiac MR exam is vital for accessibility. Manual cardiac view planning is a multi-step process customized for the patient’s anatomy and subject to operator variability. Deep learning (DL) is rapidly advancing in the medical field and has been proposed to address this; however, previous DL-based methods rely on extensive manual annotations and involve multiple models.This thesis builds on DeepCardioPlanner, a single-view planning DL tool. We proposed DeepPlanner4Cardio, a multi-view DL model predicting four cardiac views simultaneously from low-resolution 3D Cardiac MRI by leveraging inter-view relationships, reducing computational demands, and improving scalability. DeepPlanner4Cardio trains in under 3 minutes, a significant improvement over models requiring up to 19 hours. Two Cardiac MRI experts evaluated the planning accuracy of DeepPlanner4Cardio, confirming its clinical relevance with 67.5% accurate predictions and 26.5% acceptable ones. This fully automated tool offers a faster, more accessible solution for Cardiac MRI planning.

Spin Glass Phenomenology in Frustrated Magnetic Spinners
2024-11-28 14:00 - 16:00 | Sala P3 - Piso 1 Edifício de Matemática
Os vidros de spin são sistemas magnéticos caracterizados por desordem na força das suas interações, cuja complexidade impede que sejam estudados recorrendo a métodos convencionais. Foram desenvolvidos formalismos teóricos para estudar as suas paisagens energéticas, mas a validação dos resultados torna-se um desafio na ausência de sistemas físicos macroscópicos para testar propriedades através de observação direta. Este trabalho visa estudar a paisagem energética de configurações macroscópicas de spinners magnéticos numa rede, procurando observar se exibem fenomenologia de vidro de spin, comparando observações físicas com resultados das simulações. Serão estudados estados fundamentais e metaestáveis, assumindo que a razão entre a energia de ativação de um evento e a energia térmica é suficientemente grande para congelar o sistema em mínimos locais.O estudo de linhas de spinners concluiu que o número de estados encontrados cresce exponencialmente com o tamanho do sistema, uma propriedade dos vidros de spin. Simulações de redes hexagonais, tetragonais e ortorrômbicas mostraram que, em sistemas maiores do que spinners, os valores de energia por spinner dos estados formam distribuições Gaussianas com média constante e desvio padrão a tender para zero, à medida que o tamanho do sistema aumenta, resultando em sistemas infinitos cujas configurações estacionárias possuem um único valor de energia por spinner. Os conjuntos de estados exibem estrutura cada vez mais ultramétrica, quando se consideram métricas locais específicas. Assim, estes sistemas revelam apresentar fenomenologia vítrea. Trabalhos futuros centrar-se-ão na dinâmica, para explorar todos os estados possíveis em que um vidro de spin pode ser observado.

Robust Anomaly Detection in Independent Searches for New Physics with the ATLAS/LHC Experiment
2024-11-28 14:00 - 16:00 | Sala de Formação Avançada - Piso 2 Pavilhão de Física/Online
This work explores a model-independent approach based on Anomaly Detection techniques to search for New Physics phenomena in the ATLAS experiment at the LHC. Focusing on a fully-hadronic topology characterized by large missing transverse energy and at least one large-R jet with high momentum, we explore semi-supervised Machine Learning methods trained on a broad region of Standard Model simulated events, making them sensitive to New Physics signals manifesting as anomalies.First, we assess the sensitivity of both deep (AutoEncoder and Deep SVDD) and shallow (Isolation Forest) implementations to a wide topology of benchmark signals, with varying signatures and acceptances within the search space. The performance of the proposed models is benchmarked with relevant kinematic variables.Second, to improve robustness against instrumentation limitations such as systematic uncertainties arising from experimental calibrations and reconstruction of missing transverse energy and large-R jets, we implement an adversarially-trained AutoEncoder. Our findings evidence the strong potential of these techniques in the independent searches beyond the Standard Model, having achieved high sensitivity to diverse signatures and strong resilience to data uncertainties.

Numerical relativity in effective field theories of gravity
2024-11-28 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
The age of gravitational-wave astronomy is now in full swing: For the first time, we gain observational access to the highly dynamical strong-field regime of the gravitational interaction. Constraining potential deviations from General Relativity (GR) requires reliable waveform predictions, not just in GR, but also when higher curvature corrections contribute to the dynamics. I will present an overview of recent progress on (i) mathematical well-posedness, (ii) physical time evolution in the presence of ghosts, and (iii) resulting numerical nonlinear waveforms. In combination, the above constitutes a feasible pathway to use current and future gravitational-wave observations to constrain effective field theories of gravity. Items (i) to (iii) are based on three ongoing collaborations: 2407.08775, ... (with P. Figueras and A Kovacs); 2305.09631, ... (with C. Deffayet, S. Mukohyama, and A. Vikman); 2104.04010, 2306.04725, ... (with H. Lim).

New Physics searches at the LHC using Anomaly Detection
2024-11-28 16:00 - 18:00 | Online/Sala de Formação Avançada
Experiências de colisionadores são uma ferramenta importante no contexto de descobertas em física de altas energias. Esta tese contribui para a investigação sobre como se pode procurar por nova física, de forma independente de modelos teóricos, no contexto de deteção de anomalias com aprendizagem semi-supervisionada. Várias buscas por nova física utilizam estados finais de jatos para investigar novas ressonâncias. Nesta tese, o foco está na deteção de anomalias ao nível do jato, explorando sua substrutura. O jato é representado como um grafo, e cada nó é um constituinte hadrónico associado ao jato durante a reconstrução. São gerados eventos simulados de hipotéticos Jatos Escuros, enquadrados num modelo de Matéria Escura, para servirem como sinal para desenvolvimento e teste dos modelos. Esses eventos são mediados por um bosão Z' que liga um par de quarks a um par de quarks escuros, que se fragmentam e hadronizam no setor escuro até decaírem em partículas do Modelo Padrão, criando os jatos escuros. O fundo utilizado consiste em eventos de di-jatos QCD. O objetivo é extrair um vetor que mapeie a informação complexa do grafo para um vetor de baixa dimensionalidade, utilizando operações de convolução de grafos e agregação. O vetor resultante é fornecido a métodos de deteção de anomalias, como DeepSVDDs e Autoencoders, que realizam a previsão da natureza do jato devolvendo um índice de anomalia. São realizadas comparações da performance desses modelos com modelos base

An electric model of the human heart
2024-11-29 14:00 - 16:00 | Sala P3 - Piso 1 Edifício de Matemática
A implementação de uma abordagem analítica baseada nas leis físicas ao estudo do coração humano é um passo inevitavel na substituição do em pirismo associado ao conhecimento médico usado para diagnosticar e tratar pacientes. Estas abordagens não são novas, e já foi realizado um trabalho extenso na aplicação de modelos matemáticos a problemas relacionados com o funcionamento elétrico do coração humano. No entanto, estes estudos in silico são conduzidos utilizando geometrias que não têm semelhança com o órgão em questão, simulando apenas partes de tecido em vez de todo o coração. Neste trabalh o, apresentamos um modelo de todo o sistema de condução elétrica do coração humano e um procedimento para calcular as 3 primeiras derivações do Eletrocardiograma padrão de 12 derivações. O modelo e o procedimento de ECG são depois comparados com dados clínicos provenientes de uma base de dados de atletas de alto rendimento noruegueses [1]. Os resultados estão em grande concordância com o ECG registado para o atleta 5 da referida base de dados. Após a validação do modelo e do procedimento de cálculo do respetivo ECG, são introduzidas patologias relacionadas com o sistema de condução elétrica do coração para analisar os resultados do sinal de ECG.Alguns dos resultados desta análise destacam as limitações do modelo, mas de um modo geral, as ondas do ECG estão em concordância com os dados clínicos. Concluímos que é viável criar um modelo simples, tanto do ponto de vista geométrico como computacional, alcançando ainda assim resultados clinicamente relevantes.

In-medium Gluon Radiation in General Kinematics
2024-12-03 08:30 - 11:00 | Online (Password: [REDACTED]
Na sequência de colisões de iões pesados, forma-se um estado desconfinado da matéria conhecido como Plasma de Quarks e Gluões (QGP). Um dos efeitos mais estudados decorrentes da presença de um meio é o jet quenching, que se refere à perda de energia sofrida pelos jatos quando atravessam o QGP. Esta perda de energia é causada, principalmente, por interações induzidas pelo meio, que estimulam a emissão de partões a grandes ângulos. Estes partões emitidos são, ultimamente, detetados fora do cone do jato, levando a uma aparente supressão na energia medida. Dada a continua melhoria da precisão dos observáveis de jet quenching, a necessidade de ferramentas analíticas mais precisas, para descrever, com exatidão, as emissões de gluões num meio tornou-se imperativa.Este trabalho centra-se na descrição teórica das emissões induzidas pelo meio, no âmbito do formalismo BDMPS-Z. Com base em desenvolvimentos recentes, estendemos os resultados anteriores para o espetro de radiação de uma única emissão induzida pelo meio, que estava anteriormente restrito ao regime soft. Derivamos uma expressão para o espetro de emissão, sem nos basearmos nas aproximações harmónicas ou single hard, e demonstramos que esta se reduz ao resultado estabelecido no limite soft.Em seguida, fornecemos um algoritmo baseado num conjunto de equações diferenciais, concebido para simplificar a avaliação do espetro, evitando assim integrações numéricas. Por fim, ilustramos a sua aplicação utilizando a aproximação de grande.

A framework for studying CO₂ microwave plasmas
2024-12-03 10:00 - 12:00 | Online
Esta dissertação apresenta um framework abrangente para o estudo de plasmas micro-ondas de CO₂, com ênfase específica na determinação da temperatura do gás dos plasmas. A pesquisa visa desenvolver e aprimorar ferramentas para caracterizar plasmas de baixa temperatura, alinhando-se no quadro de validação passo a passo usado no N-PRIME. Os principais objetivos deste trabalho incluem o desenvolvimento de ferramentas focadas na caracterização da temperatura do gás através da modelação e da análise de espectros de emissão óptica, a integração de modelação cinética zero-dimensional (0D) com descrições fluidas para simular dados experimentais relacionados à temperatura do gás e à conversão de CO₂, e a análise dos espectros rotacionais das bandas de C₂ e N₂⁺, criando scripts dedicados para a extração de dados e realizando comparações com ferramentas de simulação existentes.A dissertação investiga vários sistemas de plasmas micro-ondas, incluindo uma tocha de injeção axial de hélio atmosférico (AIT) utilizada para validar a modelação fluida. Também examina uma tocha coaxial de CO₂ atmosférico e um reator coaxial de N₂, ambos analisados através de espectroscopia de emissão óptica (OES) para determinar temperaturas rotacionais e vibracionais. Além disso, o estudo explora descargas de CO₂ micro-ondas a baixa pressão, tanto nas regiões ativa como na pós-descarga, para avaliar a capacidade do modelo combinado de representar com precisão a distribuição espacial da temperatura.Esta pesquisa estabelece com sucesso o framework proposto, demonstrando uma forte concordância com os dados experimentais. Os resultados confirmam a eficácia das metodologias desenvolvidas na caracterização precisa das temperaturas dos gases e na melhoria da compreensão do comportamento de plasmas micro-ondas.

Searching for HWW Anomalous Couplings with Simulation-Based Inference
2024-12-03 10:30 - 13:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso /Online
(Password: [REDACTED] ) A assimetria entre matéria e antimatéria no universo é uma das grandes questões em aberto na física de partículas. Explicar este desequilíbrio exige uma fonte de violação de Carga-Paridade não prevista pelo Modelo Padrão. Dado o papel do bosão de Higgs na quebra de simetria electrofraca, as suas interações são um ponto de partida para investigar acoplamentos anómalos. Neste trabalho, estuda-se o vértice de interação HWW no canal ( ), no contexto da Teoria Efetiva de Campo do Modelo Padrão.A sensibilidade a dois acoplamentos anómalos, e é analisada usando técnicas de inferência baseadas em aprendizagem automática. Estes métodos aproveitam a informação do simulador para treinar redes neuronais que estimam razões de verosimilhança, captando correlações entre observáveis e evitando aproximações dos métodos tradicionais. O método ALICES, um estimador de entropia cruzada, é comparado com o SALLY, um observável ótimo ao nível do detetor, e com histogramas de observáveis cinemáticos e angulares.As técnicas ALICES e SALLY proporcionaram limites mais apertados do que os obtidos com observáveis 1D, mas os resultados do SALLY foram próximos dos de histogramas 2D. No entanto, o SALLY continua promissor pela capacidade de analisar vários acoplamentos simultaneamente. O ALICES, embora tenha dificuldade em captar o mínimo e a forma da verosimilhança com precisão, pode permitir uma maior sensibilidade a estes acoplamentos com refinamento adicional. Estes resultados reforçam a importância de explorar estes métodos com dados da Run 3 para melhorar os resultados de ATLAS e CMS.

Planning for muon tomography campaigns in urban settings
2024-12-03 13:30 - 15:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)/Online

3D printing nanoporous separation materials – towards scalable and sustainable membrane production
2024-12-03 14:00 - 16:00 | Seminar Room Physics Building - 2nd floor
Over the past 20 years, 3D printing technologies have emerged as innovative tools to generatemacro-porous materials, with potential in complex structures impossible to otherwise developby traditional manufacturing. More recently, advanced composite materials have beendeveloped at the mili and micro scale following progress in new polymers and resinsformulations as well as greater resolution control for both Fused Deposition Modelling (FDM)and Dynamic Light Polymerisation (DLP). Breaching the micron-scale barrier, to generate nano-porous materials has however remained to date a major challenge, due to either rheologicallimitations or minimum printable pixel size achievable. New strategies arising from polymermonoliths development have however emerged to generate ultra-porous materials, withmacron-sized thicknesses and yet nanoscale pores. Our team has developed innovativestrategies based on advanced resins formulations to print nano-porous membranes, and nano-textured catalysts as well as adsorbents. In this presentation, the feasibility to develop complex3D membrane architectures with the novel process will be demonstrated for a range ofchemistries and materials. Nanocomposite structures with excellent nano-load distributions andincorporation into porous polymeric matrixes will also be demonstrated.

Universal Properties of Non-Markovian Dissipative Quantum Systems
2024-12-03 14:00 - 16:00 | Sala P3 Pavilhão de Matemática, Piso 1/Online
In this work, we study the spectral, steady-state, and transport properties of a generic non-Markovian quantum system of free fermions. We consider a setup connected to two reservoirs atthe same temperature and with symmetric chemical potentials. The systemâ€™s Hamiltonian and its coupling to each reservoir are described by random matrices from the Gaussian unitary ensemble and the Laguerre unitary ensemble, respectively. By analyzing the Liouvillian spectrum, we observe that it is similar to the Markovian counterpart and remains unaffected by the characteristics of the environment. We compute the evolution of the decoherence rates and of the non-Markovian measure $f_{nM}$, verifying that they approach a stationary regime. Further, we examine the Markovian limits and explore the distribution of decoherence rates across different limiting cases. For the remaining parameter space, we focus on particular regions where we are able to make analytical or empirical statements. Lastly, we investigate conductance fluctuations, presenting novel numerical results for the dependence of conductance variance on parameters $m$, the decoherence channel density, and $g$, the environment coupling. This deviates from the expected universal conductance fluctuation value for random matrices.

Imaging from underground with muography
2024-12-03 15:00 - 17:00 | Sala de Formação Avançada do DF, Pavilhão de Física, 2º piso/Online
Muografia é uma técnica de imagiologia utilizada para estudar grandes estruturas como edifícios, vulcões ou pirâmides. Esta tese foi desenvolvida como parte da colaboração LouMu, que pretende testar a muografia pela primeira vez em Portugal, ao aplicar esta técnica na mina do Lousal. Pretende-se avaliar o potencial e a sensibilidade da muografia para aplicações futuras.Muografia de transmissão, como o nome sugere, analisa a transmissão do fluxo de muões atmosféricos através de um objeto para o estudar. A técnica é promissora, pois utiliza um fluxo natural e não perturbativo.Esta tese pretende fornecer uma análise sistemática do conhecimento adquirido com muografia na mina do Lousal. Os dados foram recolhidos utilizando um telescópio de muões, um aparato que permite detetar muões e reconstruir a sua trajetória. O telescópio recolheu dados em duas posições num antigo paiol da mina, intercetado por uma falha geológica. Esta falha foi o alvo da muografia. Imagens 2D de muografia foram produzidas e o nosso objetivo final é combiná-las para criar uma reconstrução 3D da mina.Neste trabalho, as imagens obtidas até agora são apresentadas e é explicado o desenvolvimento de uma função para descrever as eficiências do telescópio. A função mostrou grande promessa com simulações, no entanto, os resultados obtidos com os dados ainda precisam ser melhorados. Conhecimento valioso foi adquirido com este trabalho e, no futuro, mais aplicações da função serão estudadas.

Improved Binary Black Hole Initial Data
2024-12-03 16:00 - 18:00 | Sala P3 Pavilhão de Matemática, Piso 1
Esta tese foca-se em melhorar dados iniciais para simulações de binárias de buracos negros produzidas em relatividade numérica. Hoje em dia, o método mais usado é construir dados iniciais conformalmente planos, que são óptimos modelos para descrever os buracos negros, mas falham em captar a radiação na zona distante. Aqui reproduzimos um método de adicionar radiação aos dados iniciais, resolvendo as equações de restrição num código de excisão.As equações de restrição são resolvidas, recorrendo ao método de decomposição XCTS, para dados iniciais com radiação derivada de uma aproximação Pós-Newtoniana. Conseguimos evoluir o sistema de massas iguais e grande separação, mas, devido a limitações computacionais, foi impossível evoluir para pequenas separações, onde a radiação é mais relevante. Ajustando a métrica na zona interior, foi possível resolver as equações de restrição e evoluir o sistema para uma separação menor. Nos início da evolução, observou-se a radiação gravitacional que se esperava. Os resultados sugerem que as soluções para as equações de restrição dos dados iniciais dependem bastante dos dados de fundo na zona interior e das condições fronteira, afetando a evolução e resultados inerentes. Os resultados também indicam um efeito significativo da resolução na qualidade das formas das ondas gravitacionais extraídas.Em trabalhos futuros, iremos explorar os efeitos da radiação dos dados iniciais na transição para ondas geradas pela evolução, correndo vários testes com alta resolução. Os resultados deste trabalho irão fornecer uma melhor compreensão dos efeitos dos dados iniciais na evolução de sistemas de binárias de buracos negros e na qualidade das formas das ondas gravitacionais extraídas.

Axion dynamics in spin -1/2 quantum plasmas
2024-12-04 10:00 - 12:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Os axiões, partículas hipotéticas propostas como uma solução elegante para o problema da violação de simetria CP em Cromodinâmica quântica (QCD), ganharam atenção como candidatos promissores a matéria escura. Consequentemente, tem havido um grande interesse em compreender as suas interações com a matéria e a luz em condições específicas. Este trabalho investiga o comportamento dos axiões em plasmas quânticos de spin-1/2, com particular incidência em regimes de alta densidade e baixa temperatura, onde os efeitos de spin e as interações axião-eletrão podem revelar novas dinâmicas. Utilizando técnicas da teoria quântica dos campos e da física dos plasmas, esta investigação desenvolve uma nova teoria de Eletrodinâmica-axião quântica, capaz de descrever a dinâmica dos axiões em plasmas quânticos de spin-1/2. O estudo examina a hibridação dos modos bosónicos presentes neste ambiente (axiões, plasmões e magnões) e explora os seus efeitos na propagação de ondas electrostáticas e electromagnéticas, determinando a sua nova relação de dispersão. Estas descobertas não só aumentam a nossa compreensão das interações axiónicas em plasmas quânticos, como também visam inspirar novos métodos de deteção de axiões em ambientes de plasma de estado sólido e ultra-frio, criando potencialmente novas abordagens experimentais na física axiónica.

Learning Reduced Nonlinear Plasma Models from Data
2024-12-04 12:00 - 14:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Esta tese explora o uso de técnicas de Machine Learning (ML), com particular destaque para Sparse Regression (SR), visando a obtenção de modelos reduzidos, não lineares e interpretáveis de plasmas, obtidos a partir de dados de simulações Particle-In-Cell (PIC) de primeiros princípios.Para uma familiarização inicial com a técnica de SR, as suas vantagens e limitações, esta é primeiro aplicada aos dados da instabilidade de dois fluxos de eletrões. Dá-se particular ênfase à importância de utilizar uma formulação integral de SR para lidar com dados intrinsecamente ruidosos provenientes de estatísticas de partículas finitas.Em seguida, a técnica de SR é aplicada ao estudo das dinâmicas não lineares acústicas de iões em palsmas, usando simulações PIC para simular a evolução do plasma. Em particular, SR é empregue para recuperar a equação do momento dos iões a partir dos dados destas simulações sob diferentes condições. Motivada pelos resultados sobre ondas acústicas de iões, a técnica de SR é então aplicada para recuperar a equação de Korteweg-de Vries (KdV), tanto em dados gerados diretamente a partir das soluções analíticas como a partir de simulações PIC de primeiros princípios, totalmente cinéticas. Mostra-se que em regimes fracamente não lineares, para a equação de KdV, mesmo níveis muito baixos de ruído impõem fortes limitações à recuperação de derivadas de ordem superior. Estes resultados têm importantes implicações para futuras aplicaões de SR na descoberta de modelos não lineares reduzidos a partir de dados. Estas implicações e as direções de investigação futuras são discutidas.

Towards Hyperboloidal Numerical Relativity with the Einstein Toolkit
2024-12-04 14:00 - 16:00 | Online
O objetivo da relatividade numérica hiperboloidal é evoluir as Equações de Campode Einstein em fatias hiperbólicas compactificadas, que são do tipo espaço em todaparte e que se estendem suavemente até o infinito nulo futuro. Esta é a região emespaço-tempos assintoticamente planos atingida pelos raios de luz que saem dosistema. Incluir o infinito nulo futuro num domínio computacional finito é ideal paraa extracão de ondas gravitacionais, que tipicamente é feita por extrapolacão ouExtração Característica de Cauchy. No entanto, estes métodos introduzemimprecisões numéricas nas ondas extraídas e não são, em princípio, uma soluçãocompleta para o problema. Neste trabalho, evoluímos modelos simplificados darelatividade geral em espaco-tempos de fundo usando fatias hiperbólicascompactificadas. Para isso, usamos o Einstein Toolkit, um programa extenso e decódigo aberto construído para suportar simulações de relatividade numérica.Resolvemos os modelos em primeira ordem no tempo e no espaço e obtemos boaconvergência. Este trabalho marca a primeira implementação bem sucedida de fatiashiperbólicas compactificadas no Einstein Toolkit. É um passo fundamental para odesenvolvimento futuro destes métodos usando este programa, e demonstra opotencial que tem para aplicacões na relatividade numérica

Nonlinear optics for Ultrashort High Intensity Pulse Amplification
2024-12-04 15:00 - 17:00 | Anfiteatro QA02.4, Torre sul, Piso -2, Campus da Alameda
Amplificação óptica paramétrica de pulso chirpado (OPCPA) é uma técnica que permite a amplificação de pulsos laser ultracurtos de alta intensidade. O objetivo desta tese é montar e optimizar um sistema de OPCPA no Laboratório de Lasers Intensos (L2I) no Instituto Superior Técnico (IST), permitindo a geração de pulsos de alta intensidade com durações de poucos femtosegundos.Este sistema é alimentado por um laser infravermelho com comprimento de onda 1.03 mm, taxa de repetição de 100 kHz, duração do pulso ajustável entre 0.1 e 1 ps e máximo de 0.64 mJ. Um pulso amplificado comprimido (fs) ainda não foi obtido. No entanto, recorrendo a Amplificação Paramétrica com um cristal de YCOB, nesta tese foram alcançados pulsos com largura de banda suficiente para suportar durações até 38.8 fs e amplificações de 30 vezes.Esta tese descreve em detalhe todo o processo de amplificação, incluindo a montagem experimental usada, os estudos realizados sobre os processos de suporte necessários à amplificação (Geração de Segunda Harmonica e Geração de Supercontinuo), e os dados preliminares do pulso amplificado. Estes dados são também comparados com resultados publicados relativos a experiências semelhantes. No fim, é também detalhado o que se espera da continuação deste projeto que ainda está a decorrer.

Second-Order Couplings in Ultrashort Pulses with Cylindrical Symmetry
2024-12-05 11:00 - 13:00 | Sala P3 Pavilhão de Matemática, Piso 1
Com avanços tecnológicos na área da geração de pulsos ultra-curtos, temos a possibilidade de obter pulsos com durações muito inferiores às que conseguíamos anteriormente. No regime do pico/femto segundo (10-12 \ 10-15s), efeitos como os Acoplamentos Espaço-Temporais não são negligenciáveis, tendo impacto na forma e distribuição espectral de um pulso ultra-curto. Nesta tese, é feito um estudo sobre os efeitos de Acoplamentos de Segunda Ordem, do tipo (xi - ϒ xi) 2 (não documentados até à data), para as seguintes combinações de coordenadas: (x,t); (x,ω); (kx, ω); (kx,t), para um total de oito tipos de acoplamentos diferentes. Estes oito acoplamentos foram testados num pulso simulado numericamente propagado desde z=0 μm até z=30 μm. A visualização dos diferentes resultados foi feita através de gráficos de Intensidade 2D nos quatro domínios diferentes, e de Spectrograms, que permitiram uma visualização intuitiva da distribuição espectral dos pulsos gerados. Foi proposta e feita uma análise de resultados usando o cálculo numérico de um Coeficiente de Pearson quadrático, usado para medir a força do acoplamento entre cada coordenada. Este método foi considerado apropriado para alguns domínios, e pouco ou nada eficaz para outros (dependendo do tipo de acoplamento). O código usado foi escrito em Wolfram Mathematica.

Extended thermodynamics, quantum inequalities and cosmic censorship on the brane
2024-12-05 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
In this talk, I use braneworld holography to explore some fundamental aspects of black hole physics. On the one hand, the braneworld scenario is a natural framework for studying extended black hole thermodynamics. In particular, a dynamical cosmological constant can be incorporated by varying the brane tension. On the other hand, the black hole solution on the three-dimensional brane — the qBTZ black hole — offers a testbed for studying geometric inequalities in semiclassical gravity, such as the Penrose inequality, and its relation with weak cosmic censorship.

Minimal U(1) two-Higgs-doublet models for quark and lepton flavour
2024-12-06 14:00 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
O Modelo Padrão (MP) da física de partículas descreve, com uma precisão impressionante, inúmeros fenómenos relacionados com as interações entre os constituintes fundamentais da matéria. No entanto, as observações das oscilações de neutrinos implicam a existência de neutrinos massivos e de mistura leptónica, os quais devem ser explicados através de extensões do MP. Além disso, o MP carece de um princípio orientador para explicar as massas observadas dos fermiões e os seus padrões de mistura — o que é conhecido como o puzzle do sabor.Nesta tese, abordamos o puzzle do sabor no contexto do 2HDM, complementado por simetrias Abelianas horizontais e pela geração de massa dos neutrinos através de operadores de Weinberg efetivos. Para tal, realizamos uma análise sistemática para determinar os padrões mínimos de sabor de quarks e leptões impostos por essas simetrias, compatíveis com as massas observadas dos fermiões, padrões de mistura e fases de violação de CP. Desta forma, determinamos quatro modelos mínimos para os quarks, onde o número de parâmetros independentes corresponde ao número de observáveis. Para o sector leptónico, são identificados três modelos preditivos mínimos. Nomeadamente, encontramos cenários com uma preferência pelo octante superior/inferior do ângulo de mistura atmosférico , para os quais existem limites inferiores para as massas do neutrino mais leve, atualmente investigados pela cosmologia e testáveis em futuras experiências de decaimento duplo beta sem neutrinos, mesmo para massas de neutrinos ordenadas de forma normal. Investigamos a fenomenologia de cada modelo, tendo em conta todos os observáveis teóricos relevantes, incluindo de precisão eletrofraca, as restrições do sector escalar, bem como processos de sabores de quarks, como , e oscilações de mesões, e os decaimentos de violação de sabor leptónico carregado e Mostramos que, em alguns casos, as simetrias Abelianas de sabor fornecem uma estrutura natural para suprimir acoplamentos neutros que mudam o sabor e levam a cenários que apresentam massas de escalares neutros/carregados pesados abaixo da escala de TeV, ou seja, ao alcance de experiências atuais.

Optimizing Gallium Oxide Thin Films for Electro-Optical Applications
2024-12-06 16:00 - 18:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Óxido de gálio é um semicondutor de hiato largo que tem demonstrado grande potencial nos últimos anos devido às suas propriedades opto-eletrónicas distintivas. Em particular, o seu elevado campo elétrico de rutura, bem como a possibilidade de modificar o seu índice de refração e hiato energético tem tornado este material um candidato promissor para uma ampla gama de aplicações, como fotodetetores no UV profundo, guias de onda óticos com baixas perdas ou até mesmo células solares transparentes. Entre possíveis técnicas de deposição, a pulverização catódica por radiofrequência destaca-se pela sua capacidade de produzir filmes finos com alta qualidade e a baixo custo.Neste trabalho, foi operacionalizada a câmara de deposição SentiFET, e desenhado e construído um forno para permitir a deposição a altas temperaturas. Posteriormente, um estudo exaustivo foi realizado sobre a influência de diferentes parâmetros, tais como a pressão e a potência de deposição, a temperatura e duração do recozimento pós-crescimento e o substrato utilizado, nas propriedades óticas e elétricas dos filmes finos de Ga2O3 depositados por pulverização catódica por radiofrequência. Estas amostras foram caracterizadas através de técnicas complementares como profilometria, elipsometria, transmissão ótica, espectroscopia de retrodispersão de Rutherford, difração de raios-X, microscopia de força atómica e espetroscopia de Raman, de forma a determinar as suas propriedades óticas e estruturais, composição e rugosidade da superfície. De forma a otimizar ainda mais as propriedades óticas e elétricas dos filmes, foi também avaliado o efeito da dopagem através da implantação iónica com estanho (Sn).Finalmente, foram fabricados fotodetetores interdigitados planares baseados nestes filmes, através de fotolitografia, que foram avaliados em termos da sua responsividade ótica.

Exploring the role of sheared flows in the L-H transition
2024-12-09 09:00 - 11:00 | Sala P3 Pavilhão de Matemática, Piso 1
O trasporte em plasmas toroidalmente confinados é dominado por transporte turbulento, o que resulta em perdas substanciais. Isto é parcialmente mitigado pela operação em modo H, caracterizado por gradientes de densidade acentuados e uma redução no transporte turbulento. Devido ao confinamento melhorado, o modo H é considerado o modo de operação mais favorável para reatores de fusão. Consequentemente, muitos trabalhos têm-se dedicado ao estudo da transição L-H, com foco particular no papel do gradiente de velocidade na supressão de turbulência.O primeiro objetivo deste trabalho foi avaliar a existência de um valor limiar no gradiente da velocidade perpendicular necessário para aceder ao modo H. Medições de refletometria de Doppler foram analisadas e aproximadas por \textit{splines}, calculanto o gradiente médio da velocidade nas diferentes camadas do plasma. Os resultados indicam que não há nenhum valor consistente nessa quantidade.O segundo objetivo deste trabalho foi utilizar oscilações entre modo L e H para obter uma melhor resolução radial e temporal, permitindo acompalhar detalhadamente o desenvolvimento da velocidade perpendicular, turbulência e perfil de densidade. As oscilações foram sinconizadas e a média foi calculada, resultando numa significancia estatística robusta. Os resultados indicam que a redução das flutuações é acompanhada por um aumento do gradiente de densidade, seguido de um aprofundar do poço de velocidade. Estes resultados contrariam a visão tradicional do papel do gradiente de velocidade na supressão de turbulência.

Numerical study of a fixed oscillating water column
2024-12-09 10:30 - 13:00 | Sala de Formação Avançada do DF (Sala 2-8.11 - 2º Piso do Pavilhão de Física)
Fontes de energia renováveis são críticas na transição para sistemas de energia sustentáveis. As ondas do oceano transportam maior densidade de energia comparativamente a outras fontes de energia renováveis. A Coluna de Água Oscilante (OWC) são o tipo mais promissor de entre todos os dispositivos que convertem energia das ondas em eletricidade. O primeiro passo no design de uma OWC é o desenvolvimento de um estudo numérico e o WEC-Sim é uma ferramenta robusta e potente na indústria da energia das ondas, especialmente para simular dispositivos flutuantes. No entanto, simular Colunas de Água Oscilante no WEC-Sim requer algumas alterações no programa. Este estudo relata uma melhoria no método para simulação de Colunas de Água Oscilante fixas no WEC-Sim, através da integração de uma toolbox. Um caso de estudo da Coluna de Água Oscilante de Mutriku foi realizado com o objetivo de validar a toolbox. Este estudo está dividido em duas partes. Primeiramente, uma nova tollbox para o WEC-Sim foi criada, tendo em conta os processos termodinâmicos da câmara pneumática da Coluna de Água Osiclante, tal como descrito pelo modelo do pistão. De seguida, alguns parâmetros do WEC-Sim foram ajustados para afinar a toolbox, fazendo coincidir os resultados com os de referência.Posteriormente, como a tollbox já se encontrava verificada, um estudo numérico foi realizado como exemplo ilustrativo de como a nova tollbox pode simular diferentes cenários tais como testes de decaimento livre, compressibilidade do ar, resposta a diferentes tipos de turbinas, implementação de válvulas e estratégias de controlo.

Ultra-fast lasers towards TRIR spectroscopy
2024-12-09 14:00 - 16:00 | Sala C10, Piso 1- Pavilhão Central
A espectroscopia de infravermelho resolvida no tempo (TRIR) é uma técnica importante para o estudo de dinâmicas moleculares ultrarrápidas e propriedades de materiais. Possibilita um entendimento profundo sobre processos químicos, como a formação de estruturas de DNA e reações relevantes para o desenvolvimento de medicamentos. Esta tese estabelece um sistema de espectroscopia TRIR no Laboratório de Laser Intenso (L2I), sob o Grupo de Lasers e Plasmas (GoLP) no Instituto de Fusão Nuclear (IPFN). O nosso laboratório conta com um sistema de laser de 3 μm de alta energia com 6,5 W de potência média, 40 fs de duração de pulso e taxa de repetição de 100 kHz, além de um sistema de 1,030 μm capaz de atingir pulsos de 100 fs.Com estes sistemas de lasers ultrarrápidos, podemos monitorizar estados transitórios subpicose-gundos de moléculas, avançando a nossa compreensão das interações moleculares rápidas. Testes iniciais foram realizados utilizando rodamina 6G como sistema modelo, com o laser de 1,030 μm como pulso de excitação da amostra e 515 nm como um pulso sonda. Os resultados demonstram o potencial de nosso sistema para estudos resolvidos no tempo de sistemas moleculares complexos.Com estes recursos únicos, o nosso laboratório está posicionado para fazer contribuições significativas no campo da espectroscopia TRIR ultrarrápida, com aplicações que variam da pesquisa científica básica à inovação industrial. Este trabalho prepara estabelece a possibilidade de explorar processos dinâmicos em nível molecular, capaz de fornecer dados valiosos para áreas como ciência dos materiais e bioquímica.

Higher order Hubble-induced phase transitions for gravitational production of dark matter
2024-12-09 16:00 - 18:00 | Online
Esta tese apresenta um novo mecanismo para a produção gravitacional de matéria escura(DM), com o objetivo de gerar a atual abundância observada de DM num vasto leque deparâmetros. Construímos um modelo teórico baseado em acoplamentos gravitacionais desegunda ordem e examinamos sistematicamente a sua dinâmica e eficiência.Recorrendo a na proximações analíticas e, principalmente, a uma exploração detalhada do espaço deparâmetros envolvendo ~200 simulações, investigamos o comportamento do modelo para diversas configurações. Esta extensa análise numérica permitiu-nos derivar funções de ajuste que interpolam com precisão os resultados em toda a região permitida do espaço de parâmetros. Os resultados demonstram que o nosso modelo consegue produzirconsistentemente a abundância necessária de DM numa ampla faixa de valores,confirmando a sua flexibilidade e robustez. Este trabalho serve como um estudo primário,oferecendo uma estrutura simplificada mas poderosa que pode ser estendida e refinadapara modelos mais abrangentes de produção gravitacional de DM

Neural systems that process visual self-motion cues in larval fish: a comparative approach
2024-12-10 10:00 - 12:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso /Online
Os modelos animais são amplamente utilizados na ciência, com o peixe-zebra, Danio rerio, ocupando um papel fundamental na neurociência.No entanto, alargar a variedade de espécies estudadas é essencial para testar a generalização dos princípios e explorar as causas de diversidade comportamental. Esta tese expande métodos utilizados para o estudo do comportamento visual em larvas de peixe-zebra a outras espécies, como o danio gigante, Devario aequipinnatus, e a danionella, Danionella cerebrum.Utilizando imagens funcionais de dois fotões em peixe-zebra e danio gigante, foi desenvolvido um protocolo para avaliar as respostas neuronais a grelha em movimento e o ajuste a velocidades diferentes. O peixe-zebra demonstrou respostas diferentes ao movimento para a frente e para trás, mas o danio gigante apresentou uma fluorescência inconsistente, limitando a análise.Para o estudo da resposta optomotora binocular, um estímulo e protocolo foram desenhados e testados nas três espécies. Embora as respostas angulares tenham sido semelhantes entre as espécies, os deslocamentos lineares diferiram. O peixe-zebra e a danionella apresentaram respostas de fundo comparáveis, enquanto o danio gigante exibiu respostas significativamente mais elevadas, o peixe-zebra e o danio gigante a apresentarem também respostas aumentadas para movimentos direcionados para a frente, um padrão ausente na danionella.Por fim, foi construída uma montagem para capturar imagens de larvas em alimentação para estudar o comportamento de caça em peixe-zebra e danio gigante, com este último a demonstrar uma maior taxa temporal de consumo. Um modelo SLEAP foi treinado para adicionar o seguimento de olhos e barbatanas ao existente da cauda, o que, combinado com dados de localização de presas, fornece uma caracterização detalhada das sequências de comportamento de caça.

Evaluation of the Magnetic Susceptibility in Cardiac Tissues using Magnetic Resonance Imaging. Quantitative Susceptibility Mapping for the Quantification of Heart Valve Calcification using a Calcium Phantom
2024-12-10 14:00 - 16:00 | Sala C10, Piso 1 - Edifício Central/Online
A calcificação das válvulas cardíacas é uma doença crónica, degenerativa e clinicamente relevante. Resulta da anormal acumulação de sais de cálcio.Neste trabalho preliminar, pretendeu-se estudá-la utilizando o Mapeamento Quantitativo de Suscetibilidade (QSM), uma técnica de RM que mede a suscetibilidade magnética dos tecidos. É sensível ao cálcio, como a Tomografia Computorizada (TC), o procedimento-padrão para o diagnóstico de calcificações. Contudo, não envolve radiação ionizante.Para reproduzir o tecido calcificado, fez-se um fantoma de agarose com carbonato de cálcio (CC) e hidroxiapatita (HA). Adaptando sequências 3D gradient-echo existentes e software de reconstrução QSM para o cérebro, obteve-se um protocolo de aquisição e pós-processamento para o fantoma, basedo em estudos anteriores de RM cardíaca.Conseguiu-se detetar calcificações com cerca de 2 mm, próximo da resolução espacial. Suspeita-se que possam ser detetadas concentrações de cálcio até 0,30 M e inferiores a 0,25 M, para CC e HA, respetivamente. Os resultados indicam que a suscetibilidade diminui linearmente com o teor de cálcio e que a HA é mais diamagnética que o CC, coerente com o facto de ser o principal responsável pelas calcificações e apontada como um biomarcador de malignidade. Porém, isto parece ser atenuado na presença de outros sais de cálcio. Aí o teor total de cálcio é mais relevante. Finalmente, a relação entre o coeficiente de atenuação e a suscetibilidade, aparentemente linear para a mesma composição, foi investigada, confirmando a composição diversificada das calcificações.Embora não possibilite uma análise bioquímica completa, o QSM é promissor na deteção e quantificação do cálcio.

Ergodicity and Entanglement: Bridging Random Matrix Theory and Many-Body Quantum Systems
2024-12-11 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Thermalization is deeply connected to the notion of ergodicity in the Hilbert space, implying an equipartition of the wave function over available many-body Fock states. Under unitary time evolution, an initially structured state spreads in the Fock space, approaching a Haar random state, thereby highlighting a connection between many-body quantum systems and random matrix theory. In the first part of this talk, I will discuss the dynamics of the self-dual kicked Ising model, a minimal model of many-body quantum chaos that is unitary in both time and space. I will focus on its dynamics in Fock space, showing how the probability distribution of the initial state approaches that of a random state (Porter-Thomas distribution). In the second part, I will explore some general relationships between entanglement and the spread of the wave function in Fock space. Remarkably, I will demonstrate that entanglement entropies can still exhibit fully ergodic behavior, even though the wave function occupies only a vanishing fraction of the full Hilbert space in the thermodynamic limit.

Imaging ultra-compact objects with radiatively inefficient accretion flows
2024-12-12 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Recent Event Horizon Telescope (EHT) observations of M87* and Sgr A* provide compelling evidence for the presence of supermassive black holes at their respective cores. However, alternative models for these compact objects remain plausible. In the talk, we will explore the observational signatures of Joshi-Malafarina-Narayan (JMN-1) naked singularity (which emerges as an end state of a continual gravitational collapse) by employing a semi-analytic Radiatively Inefficient Accretion Flow (RIAF) model to generate synchrotron emission images. Additionally I will talk about how the choice of magnetic field configuration affects the polarised images in black hole images which can further help in determining magnetic field topology near sources such as Sgr A* and M87*.

Using Novel Spectroscopy to Study the Optical Properties of Semiconducting Polymers
2024-12-18 14:30 - 16:00 | Sala de Seminários do DF, Pavilhão de Física, 2º piso
Conjugated polymers hold great promise for cost-effective electronic applications, ranging from light-emitting displays to photovoltaic systems. However, their complex morphologies, particularly in polymer blends, significantly influence optical properties and electronic transport, ultimately affecting device performance. Understanding the relationship between morphology and electronic structure required the use of diverse spectroscopic techniques. In this talk, I will highlight key insights into the behaviour of soft matter semiconductors, emphasizing the advanced spectroscopic tools employed to unravel their properties and the interplay between structure and function.

Building particle physics from the bottom up
2024-12-19 14:00 - 16:00 | Anf. Abreu Faro (Complexo Interdisciplinar)
If you are a physics student, you have probably felt that understanding physical phenomenainvolves finding the correct set of equations to describe them, and very carefully solving these equations without making any mistakes. But, surprisingly, it turns out that physical phenomena are often incredibly constrained by asking for consistency with basic physical principles, and one can more quickly and reliably "just write down the correct final answer" by making sure these are satisfied. In this talk, I will put this philosophy into practice, and show how doing physics in this way is much more forgiving of little mistakes, as we let the consistency conditions guide both our thinking and our computations. I will start with some simple examples of everyday physics and build up to understanding how relativity and quantum mechanics strongly constrain and dictate the allowed interactions of elementary particles. I will end by explaining how this way of approaching physical problems is even more powerful in the context of the most fundamental observables in particle physics -- scattering amplitudes.

Aerodynamic study of atmospheric-pressure plasma jets
2024-12-20 14:00 - 16:00 | Online
Jatos de plasma a pressão atmosférica (JPPAs) podem ser criados por descargas pulsadas repetidas produzindo ondas de ionização (OIs). O gás do jato, tipicamente um gás nobre, guia a OI que excita e ioniza espécies ao longo do jato. JPPAs frios são plasmas fracamente ionizados e preservam as propriedades mecânicas dos gases neutros. Assim, uma descrição auto-consistente dos JPPAs deve incluir a dinâmica acoplada de plasma e fluido. Neste trabalho, estudamos a aerodinâmica dos JPPAs usando métodos experimentais e de modelização computacional. As experiências foram feitas com reatores a árgon para estudar as OIs (fast-imaging), o escoamento (Schlieren), a densidade de Ar(1s5) (espectroscopia de absorção a laser) e espectros de emissão ótica. Estudos de modelização usam o Software Package for Aerothermodynamics Radiation and Kinetics (SPARK), inicialmente desenvolvido para simular plasmas de reentrada atmosférica, mas adaptado nesta tese para condições típicas dos JPPA: plasmas subsónicos, não estacionários, e em condições de não equilíbrio térmico. Experimentalmente, estudamos JPPAs de árgon gerados num reator cilíndrico de descarga de barreira dielétrica (DBD) com um elétrodo exposto. O principal jato de árgon é protegido por um fluxo co-axial gasoso composto por uma mistura de N2 e O2. Aplicamos pulsos quadrados de alta tensão (4 kV a 6 kV) a alta frequência (10 kHz a 20 kHz), onde cada pulso de tensão cria duas descargas: uma na frente de subida e outra na frente de descida do pulso. A primeira descarga propaga-se como uma OI, com emissão de luz filamentar para frequências abaixo de 10 kHz e emissão difusa para frequências mais altas.A OI propaga-se na linha central do jato, com velocidades de ~2×105 ms-1 a 6 kV e ~105 ms-1 a 4 kV, mostrando espirais e ramificações perto do final da trajetória. A emissão de luz da segunda descarga é sempre difusa, mais curta e menos intensa que a primeira. O jato de árgon está num regime de transição, sendo laminar durante os primeiros 10 a 40 mm e turbulento a jusante. Uma única descarga cria uma perturbação de fluxo coerente (com formato em 'S'), que se propaga a uma velocidade próxima à do escoamento. Aumentar a frequência de repetição do pulso de tensão aplicada leva a uma progressiva redução da zona laminar. O escoamento co-axial também afeta o comprimento laminar do jato de árgon, com um menor comprimento laminar para maiores concentrações de O2. Na primeira descarga, os perfis de densidade de Ar(1s5) são mais extensos, mais amplos e menos reprodutíveis do que na segunda descarga, geralmente levando a densidades mais altas (5.4-9.3x1013 cm-3). A ausência de O2 no gás coaxial leva a uma menor reprodutibilidade e perfis de densidade de Ar(1s5) mais longos e amplos. Adicionando O2, aumenta-se a reprodutibilidade da absorbância e a densidade máxima de Ar(1s5) em ambas as descargas. Perfis espaciotemporais da densidade de Ar(1s5) mostram um aumento durante a passagem da OI, seguido por uma diminuição e um segundo aumento, possivelmente devido ao decaimento radiativo do Ar(4p). Na segunda descarga, a taxa de produção é menor do que na primeira e diminui progressivamente com a distância ao bocal. A densidade eletrónica foi estimada a partir do alargamento Stark da linha Hɑ, sendo ~4x1014 cm-3 durante a passagem da OI. A distribuição rotacional de OH mostrou características de não-equilíbrio, consistentes com uma descrição a duas temperaturas. A menor temperatura foi medida em torno de 320 K e deve estar em equilíbrio com a temperatura de translação do gás. A temperatura vibracional de N2(C) atingiu ~3x103 K durante a passagem da OI, diminuindo rapidamente nos 150 ns seguintes para ~103 K. Os estudos de modelização usaram uma versão modificada do código SPARK-CFD desenvolvida nesta tese. As adaptações relevantes foram: a inclusão da descrição dos eletrões em equilíbrio térmico não local; a inclusão de um solver de fluxo invíscido de baixa dissipação numérica; formulação e implementação numérica de pré-condicionamento a baixo Mach; a inclusão de paralelização com OpenMP; implementação de métodos de divisão de operadores para a integração temporal; implementação de condições fronteira subsónicas; e a inclusão de uma camada de esponja passa-baixo para amortecer ondas acústicas. O código foi verificado para descontinuidades no escoamento, com um solver de Riemann exato, e para a solução analítica de um jato laminar. Simulações não reativas mostram a transição de um jato difuso (completamente laminar) para um jato instável com perturbações axisimétricas com o aumento da taxa de fluxo. O escoamento dentro do reator mostra uma região de recirculação que não atinge o equilíbrio antes da saída do bocal. Esta recirculação puxa espécies de ar seco para dentro do bocal e leva a velocidades axiais máximas mais altas do que o esperado. Simulações 0D de um único pulso mostram que uma densidade de potência de, pelo menos, 1012 Wm-3 é necessária para alcançar as densidades experimentais de Ar(1s5). A densidade de Ar(1s5) aumenta após ser aplicado o pulso de potência devido a transições radiativas e colisões superelásticas de Ar(4p) e de estados eletrónicos superiores do árgon. A associação a três corpos é identificada como o principal mecanismo de destruição do Ar(1s5), que demonstra um tempo de vida coerente com resultados experimentais. Simulações de multi-pulso mostram uma acumulação progressiva de espécies reativas ao longo de múltiplos pulsos, mostrando a convergência para um estado estacionário periódico em casos de alta pureza de árgon (fração de ar seco <10-4). Nestes níveis de pureza, o Ar2 + é o ião dominante durante todo o pulso. A purezas mais baixas, o Ar2 + é rapidamente superado por O2 + , que, por sua vez, é ultrapassado por NO+ a meio período. Todas as espécies de árgon são severamente afetadas pela inclusão de ar seco, sendo destruídas para densidades residuais na pós-descarga para uma fração de ar seco ≥10-3 . Simulações radiais 1D mostram dinâmicas químicas idênticas às simulações 0D. Mostram também que a descarga cria um ligeiro (<10 K) mas rápido aquecimento de gás, levando a um aumento de pressão. A pressão aumenta apenas em regiões de alta pureza de árgon, criando assim uma descontinuidade no campo de pressão. A descontinuidade cria uma onda de choque fraca que se expande radialmente. Esta onda acelera o gás para velocidades radiais de até 3 ms-1 . Simulações 2D split usam o método de integração de Strang e o esquema cinético completo. Estas simulações mostram uma descontinuidade de pressão que se forma pelos mesmos mecanismos descritos nas simulações radiais 1D, mas dissipando-se mais rapidamente devido à maior dissipação numérica. Para um gás co-axial de 100% O2, a densidade eletrónica permanece alta na fronteira entre árgon e o gás co-axial, levando a uma maior densidade eletrónica nos pulsos subsequentes. Os iões O2 + , que são destruídos mais lentamente que outros iões positivos, retêm eletrões na fronteira jato - gás co-axial através de mecanismos semelhantes ao transporte ambipolar. Este efeito está essencialmente ausente para um gás co-axial de 100% N2. Tempos de subida e queda da densidade de Ar(1s5) estão de acordo com os resultados experimentais. Perfis de densidade locais mostram a densidade máxima de Ar(1s5) a diminuir para maiores distâncias radiais e axiais. Mostram também uma dependência não linear com a fração de O2 no gás coaxial, com uma destruição mais rápida para 50% O2, seguida por 20% O2. Simulações 2D totalmente acopladas usam uma abordagem híbrida para integração temporal, permitindo uma descrição mais precisa da criação e propagação da descontinuidade de pressão. As simulações mostram que a onda de choque se dissipa principalmente na fronteira entre o jato de árgon e o gás co-axial. Ao longo de múltiplos pulsos, a temperatura do gás aquece nesta fronteira, resultando numa camada fina de gás quente em torno do jato. Um aumento da secção transversal do jato de árgon acompanha o aquecimento do gás. A jusante da descarga, a mistura do jato de árgon segue o comportamento do caso não reativo. Entre estas duas regiões, há um perfil tipo “pinça” onde a secção transversal do jato de árgon diminui repentinamente. Pela primeira vez, exploramos os efeitos aerotérmicos dos JPPAs no contexto da descrição de múltiplos pulsos, incluindo mecanismos de acoplamento plasmaescoamento. A nova versão do SPARK-CFD desenvolvida durante a tese será lançada como código aberto. O código pode agora simular plasmas subsónicos e hipersónicos, com um acoplamento de energia melhorado entre eletrões e espécies pesadas, o que ampliará o seu uso em modelização de fontes de plasma.

Hairy black holes and bosonic stars: linear and non-linear solutions and their properties
2025-01-10 10:00 - 12:00 | Online
O paradigma do buraco negro de Kerr é, à data, o mais bem sucedido na explicaçãoda natureza dos objetos astrofísicos mais compactos do Universo. No entanto, certosproblemas teóricos em aberto, bem como as limitações das observações atuais, motivam aprocura de alternativas, cujas propriedades desafiam o paradigma vigente. Entre as muitaspossibilidades, apenas algumas parecem ser sólidas e de potencial relevância astrofísica. Éesse o caso dos buracos negros com cabelo sincronizado e das estrelas bosónicas, duasfamílias de objetos compactos exóticos cuja existência depende de campos bosónicoshipotéticos.Esta tese de doutoramento é uma compilação de trabalhos de investigação sobre afísica desses objetos compactos. Os capítulos são, na sua maioria, reimpressões detrabalhos de investigação publicados em revistas científicas com revisão por pares. OCapítulo 2 estuda em detalhe o estado fundamental dos buracos negros com cabelo deProca, nomeadamente as suas versões lineares, conhecidas como nuvens estacionárias. OCapítulo 3 discute a lógica subjacente à existência de nuvens estacionárias, que requer ummecanismo de retroalimentação. O Capítulo 4 apresenta um limite superior para a “pilosidade” de buracos negros com cabelo sincronizado formados através do crescimento e saturação do modo superradiante dominante de buracos negros de Kerr. O Capítulo 5 considera esses buracos negros cabeludos de um ponto de vista termodinâmico. Apesar de serem entropicamente favorecidos, estes objetos compactos são localmente instáveis no conjunto canónico, mesmo quando bifurcam de buracos negros de Kerr localmente estáveis, e correspondem, por isso, a uma nova fase. Por fim, o Capítulo 6 analisa perturbações radiais lineares de estrelas bosónicas esfericamente simétricas no domínio da frequência, confirmando e estendendo resultados existentes na literatura. Inclui o cálculo dos modos normais fundamentais destas estrelas, bem como uma discussão sobre critérios de estabilidade linear.

Plasma-based accelerators and light sources: an overview from the past to the future
2025-01-13 14:00 - 16:00 | Anfiteatro PA-3, Piso -1, Pavilhão de Matemática do IST

Jetography in Heavy Ion Collisions
2025-01-17 09:00 - 11:00 | Online
In the last two decades, ultra-relativistic heavy ion colliders have unlocked the study of the Quark Gluon Plasma (QGP) - a hot, dense, and rapidly expanding state of matter exhibiting both deconfinement of its partonic degrees of freedom and signatures of collective behaviour (e.g. nearly zero viscosity). Due to its extremely short lifetime (10^-24 s) the QGP is mainly studied through probes such as jets, clusterings of final state hadrons with a common partonic origin. Since jet development covers a wide range of energies, the modifications of these observables due to the QGP, known as jet quenching, provide valuable insight into QGP development.Theoretical descriptions of jet quenching still lack a unified framework for both vacuum-like and medium-induced radiation, a task complicated by the former being formulated in momentum space while the latter requires some interface with the coordinate space development of the medium. Since most state-of-the-art models postulate some space-time picture of jet development based on the splitting kinematics, we set out to explore different but equivalent formulations of vacuum-like emissions by building Monte-Carlo Parton Showers ordered in formation time, invariant mass, and opening angle, and considering the impact of these choices on a simplified jet quenching model. We find significant variation between orderings, particularly for thin media.Another shortcoming lies in the breakdown of colour coherence, which guarantees angular ordering of vacuum-like emissions. While medium-induced emissions are known to violate this condition, current results are limited by reliance on simplified scattering rates, valid only in restricted phase-space regions. Inspired by a previously introduced formalism based on Dyson-Schwinger equations, we compute the decoherence parameter of a quark-antiquark antenna in the QGP for two realistic scattering rates.

Vector-Like Quarks and Other Physics Beyond the Standard Model
2025-01-29 15:00 - 17:00 | Sala P9 - Piso 2 do Edifício de Matemática (IST - Campus Alameda)
The Standard Model (SM) was first proposed more than 50 years ago and it is still one of the most successful theories in science. There are, however, some phenomena that the SM cannot explain, such as dark matter or the matter anti-matter asymmetry. Thus, it is the job of theoretical particle physicists to propose models which complement the SM, explaining some phenomena that it cannot.One such class of models are models with vector-like quarks (VLQs). VLQs are fermions which, like the SM quarks, are triplets of SU(3) but whose left- and right-handed components transform in the same way under SU(2). On the one hand, they are motivated from the top-down approach since they appear in some Grand Unified models, such as E_6, and they also appear in some extra dimension models, such as the Randall and Sundrum warped geometry models. On the other hand, they are also motivated from the bottom-up, since they can explain deviations from unitarity of the CKM matrix and they can give new sources of CP violation. They can appear in seven different types of gauge covariant multiplets. Out of those, the singlets with hypercharges 2/3 or -1/3 and the doublets with hypercharge 1/6 are the representations which contain only fields with the same electric charge as the SM quarks, making them the simplest VLQ extensions. We have studied these extensions.There is a bigger class of models beyond the SM (which include models with VLQs), which are the models which have the same electroweak gauge group as the SM, i.e., SU(2) x U(1). For this class of models, the New Physics (NP) effects can be parametrized by a set of observables called oblique parameters. We have computed the oblique parameters in different general NP frameworks, namely in extensions of the SM with extra fermions (which include extensions with VLQs) and in extensions of the SM with extra scalars.

A novel compact gas-based nanodosimeter detector for proton therapy applications
2025-01-30 15:00 - 17:00 | Online
The major goal in the metrology of micro- or nanodosimetry is to provide physical quantities that are well suited to represent the biological effectiveness of radiation, to model it, and assess it by measurement. Absorbed dose, which has been consistently used in "macroscopic" dosimetry up to now, turns out to be unsuitable when applied to the microscale; for example, when modeling radiation effects on cells and DNA. Especially for densely ionizing particles such as low energy protons, ionization clusters occur on the nanometer scale. The quantity considered suitable for nanodosimetry is the ionization cluster size distribution, i.e., the probability distribution of ionization cluster sizes. From a metrological point of view, nanodosimeters are used to determine the ionization cluster size distributions produced by the mixed radiation field.There is an urgent need to measure and predict the formation of large ionization clusters, which are biologically most important, using a gas-based compact nanodosimeter as well as Monte Carlo track-structure simulations. Nanodosimetric quantities might replace or complement the dosimetric quantities currently in use, and could then be used in treatment planning and radiation protection. Thus, further design and testing of a compact nanodosimeter for mixed radiation fields is the objective of this work.

Characterization and Study of Film and Crystalline-based Organic Photodetectors
2025-02-04 11:30 - 13:00 | Sala de Formação Avançada do DF (2-8.11 - Piso 2, Edifício de Física)
This seminar explores the development of efficient organic photodetectors and photovoltaic devices based on organic single-crystal (OSC) molecular systems. Unlike conventional organic photodetectors and photovoltaics, which rely on amorphous or blended materials and face efficiency limitations in large-area applications, OSC-based devices offer advantages such as higher charge mobility, improved material purity, and scalable fabrication without efficiency loss. The study integrates advanced spectroscopic techniques to correlate molecular structure, morphology, material properties, and device performance, aiming to enhance the viability of organic photodetectors technology.

Breaking black-hole uniqueness at supermassive scales
2025-02-06 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In general relativity, all vacuum black holes are described by the Kerr metric. However, beyond general relativity, there is a prevailing expectation that deviations from the Kerr solution are more likely to manifest with increasing horizon curvature, making solar-mass black holes more promising grounds to test general relativity. In this talk I will challenge this expectation and discuss a model where black holes differ from Kerr only in a finite mass range, bounded from above and below. In particular, black-hole uniqueness can be broken at supermassive black-hole scales, while solar-mass black holes remain well-described by the Kerr solution.

Lindblad engineering for quantum Gibbs state preparationunder the eigenstate thermalization hypothesis
2025-02-12 11:00 - 13:00 | Sala de Formação Avançada do DF (2-8.11 - Piso 2, Edifício de Física)
Building upon recent progress in Lindblad engineering for quantum Gibbs statepreparation algorithms, we propose a simplified protocol that is shown to be efficientunder the eigenstate thermalization hypothesis (ETH). The ETH reduces circuit overheadof the Lindblad simulation algorithm and ensures a fast convergence toward the targetGibbs state. Moreover, we show that the realized Lindblad dynamics exhibits resilienceagainst depolarizing noise, opening up the path to a first demonstration on quantumcomputers. We complement our claims with numerical studies of the algorithm'sconvergence in various regimes of the mixed-field Ising model. In line with ourpredictions, we observe a mixing time scaling polynomially with system size when theETH is satisfied. In addition, we assess the impact of algorithmic and hardware-inducederrors on the algorithm's performance by carrying out quantum circuit simulations ofour Lindblad simulation protocol with realistic noise models. This work bridges the gapbetween recent theoretical advances in Gibbs state preparation algorithms and theireventual quantum hardware implementation.

Quasi-normal modes of rotating black holes beyond General Relativity
2025-02-13 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In this talk, I will summarize the recent advancements of quasi-normal modes in alternative theories of gravity. I will explain the main issues in computing the characteristic frequencies of rotating black holes and what are the most prominent strategies to tackle this problem. The approaches covered include the slow-spin and small-coupling expansions. In particular, I will present a beyond-Teukolsky approach for the computation of quasi-normal modes using the continued fraction method, and its application in several modified theories of gravity.

Formal and phenomenological studies in the high energy limit of QCD
2025-02-17 17:00 - 19:00 | Online
In high-energy hadronic scattering, particularly in the Regge limit—where the center-of-mass energy is large compared to the exchanged momentum—perturbative QCD faces challenges due to the appearance of large logarithmic energy-dependent terms that require an all-order resummation.Resummation techniques, such as the BFKL framework, lead to complex integro-differential equations, making direct phenomenological comparisons difficult. Monte Carlo methods play a crucial role in obtaining numerical solutions in momentum space, enabling direct comparison with both multi-purpose event generators and experimental data. Despite their strong theoretical motivation, resummation effects have yet to be conclusively confirmed experimentally. Specific kinematic configurations, such as Mueller-Navelet jets and diffractive processes, offer promising opportunities to isolate high-energy resummation-related effects.Our research focuses on refining theoretical calculations and developing new phenomenological observables that can be studied with Monte Carlo tools, both within resummation frameworks and general multi-purpose event generators. The final goal is to disentangle high-energy contributions and compare predictions with both current and future experimental data.

Ultrafast imaging of relativistic instabilities in solid-density plasmas
2025-02-18 11:30 - 13:00 | Anfiteatro PA2 (Piso -1 do Pavilhão de Matemática) do IST
The streaming of relativistic charged particles gives rise to kinetic instabilities that magnetize astrophysical and laboratory plasmas. These (collective) fields impact plasma dynamics and their study is critical to a wide range of systems, from cosmic-ray transport in galaxies to the solar wind to fusion plasmas. Despite their importance, the direct experimental characterization of these instabilities has remained a challenge. I will discuss the results from experiments combining a high-intensity optical laser with a high peak-brightness X-ray laser at LCLS that successfully imaged relativistic kinetic instabilities in solid-density plasmas with an unprecedented spatial and temporal resolution of 200 nm and 50 fs. The measured plasma density evolution, together with supporting theoretical analysis and kinetic simulations, reveal a unique interplay between space-charge, resistive effects and ion dynamics on the development of the instabilities. These findings further indicate that magnetic fields on the order of 1000 Tesla are produced, which help confine high-energy electrons with important implications for the transport of energetic particles in plasmas.

Constraining charge-parity symmetry violation in the interactions of the Higgs and W bosons
2025-02-19 10:00 - 12:00 | Sala P13 - Piso 2 do Edifício de Matemática (IST - Campus Alameda)/ Online
Password: [REDACTED] violation of charge and parity symmetry (CP) must have occurred in the early universe to explain the discrepancy between the hypothesis that particles and anti-particles were produced in equal numbers in the Big Bang, and the observation that the universe today is matter-dominated. This is not explained by the Standard Model. This work uses the Standard Model effective field theory framework to study anomalous couplings of associated production of a Higgs boson, decaying into two b quarks, and a W boson, decaying leptonically, focusing on , a CP-odd operator affecting this process, that can cause CP violation. Two other CP-even operators are also considered: and . The distributions of four variables were studied to probe their sensitivity to these operators - the transverse momentum of the W boson, the angular distance between the b-jets, and two angular observables. The transverse momentum and one of the angular observables were chosen as the combination of observables with a suitable sensitivity to perform a binned parameterisation of the WH associated production cross section, in terms of the anomalous contributions. This parameterisation is performed independently for the two observables and in combination, and is later used in a likelihood fit to constrain the possible values of , and so, the magnitude of the CP-odd coupling. This work uses ATLAS Run 2 proton-proton collision data, with 13 TeV, and is a contribution to a paper in preparation, studying CP violation in anomalous couplings in WH associated production, in the context of the ATLAS experiment.

Creation of Wavepackets for Quantum Chromodynamics on Quantum Computers
2025-02-19 14:00 - 16:00 | Sala de Formação Avançada Piso 2 Pavilhão de Física
One of the most ambitious goals of quantum simulation of quantum field theory is the description of scattering in real time, which would allow not only for computation of scattering amplitudes, but also for studying the collision process step by step. The initial state of such simulation is made of typically two wavepackets moving on top of the vacuum, whose preparation is difficult Some proposals are based on a modified adiabatic transformation of free wavepackets into interacting wavepackets, but this is not suitable for QCD. Other approaches used in one-dimensional lattice gauge theories rely on an adiabatic transformation from the strong coupling limit, or on ansatzes to create the wavepackets from the full, interacting vacuum. Here we extend a previous work to create wavepackets of a general kind of particle from the vacuum in lattice gauge theories in one and three dimensions, including QCD. The conceptual foundation of this approach is the Haag-Ruelle scattering theory, and the only theoretical limitation is given by massless particles. In the context of digital quantum computation, the wavepacket creation from the vacuum is implemented with the technique known as LCU (linear combination of unitaries). The preparation is performed successfully with a certain success probability, which may represent the main obstacle of our approach.

A Perspective on the Future of High-Energy Collider Physics
2025-02-19 16:00 - 18:00 | Anfiteatro PA1 (Piso -1 do Pavilhão de Matemática) do IST
The discovery of the Higgs boson opened the door to the investigation of new fundamental interactions of nature unlike any studied before. After a reminder about how certain essential features of the Higgs mechanism matter for the world around us, this talk will examine (a) what we actually know about the Higgs sector of the Standard Model (much more than we expected to, much less than is written in textbooks); (b) some key questions that could be investigated in the near and more distant futures and (c) how we might view the wider landscape of high-energy particle physics.

Late-time tails in nonlinear evolutions of merging black holes
2025-02-20 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
It has been known for many years, that the boundary condition alter the tails of scalar radiation in spherically symmetric spacetimes. It was however an open question to which extent this result generalises to gravitational waves in vacuum. Using the pseudospectral SpEC code we we uncover for the first time late-time gravitational-wave tails in fully nonlinear 3+1 dimensional numerical relativity simulations. We achieve this result by exploiting the strong magnification of late-time tails due to binary eccentricity and showcase here the tail presence in head-on configurations for several mass ratios close to unity. The impact of the boundary conditions is uncovered in a systematic study, showing that the boundary conditions are the primary source for errors in the tails. The simulations are also compared to perturbative evolutions, which display striking agreement with full nonlinear ones.

The Neutrino Dark Matter connection
2025-02-20 16:00 - 18:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building

Quasinormal Modes in Modified Gravity using Physics-Informed Neural Networks
2025-02-27 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
We apply a novel approach based on physics-informed neural networks to the computation of quasinormal modes of black hole solutions in modified gravity. In particular, we focus on the case of Einstein-scalar-Gauss-Bonnet theory, with several choices of the coupling function between the scalar field and the Gauss-Bonnet invariant. This type of calculation introduces a number of challenges with respect to the case of General Relativity, mainly due to the extra complexity of the perturbation equations and to the fact that the background solution is known only numerically. The solution of these perturbation equations typically requires sophisticated numerical techniques that are not easy to develop in computational codes. We show that physics-informed neural networks have an accuracy which is comparable to traditional numerical methods in the case of numerical backgrounds, while being very simple to implement. Additionally, the use of GPU parallelization is straightforward thanks to the use of standard machine learning environments.

Post-Maxwellian electrodynamics with neutron stars
2025-03-06 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
One of the big, open problems in gravity is whether or not black holes have singularities. In vacuum general relativity this is guaranteed via the Hawking-Penrose theorems, but by coupling to various nonlinear, electromagnetic Lagrangians it has been shown that charge may regularise the object.Physically, this is argued to be because gravity is attractive and electrostatics repulsive, preventing singularities. Some highly-magnetised neutron stars ("magnetars") have inferred polar field strengths well in excess of the Schwinger limit, where nonlinear electromagnetic effects may dominate. Their internal fields may be even stronger, meaning that Maxwellian descriptions of hydromagnetic structure may require revision. In Born-Infeld-like theories -- a popular candidate for regularizing holes -- I argue that the toroidal field has a maximum strength set by the scale parameter. Because of this, there is an implicit bound to the stellar prolateness which can be inferred via gravitational waves; detections or non-detections can thus be used to set bounds on post-Maxwellian parameters that is competitive with terrestrial experiments. Connections with black hole singularitieswill then be made.

Heavy baryon excitations with functional calculations + Diquark correlations of the baryon spectrum
2025-03-11 14:00 - 16:00 | Sala de Formação Avançada Piso 2 Pavilhão de Física/Online
Passcode Zoom (se necessária): 432293Recent years have witnessed significant progress in heavy baryon spectroscopy, with almost 30 new heavy baryon states discovered at the LHC. On the theoretical front, many methods have been employed to study baryon spectroscopy, such as quark models, effective field theories and lattice QCD. All have with their own advantages and drawbacks, such as the challenges posed by excited states in lattice QCD, the limited range available in effective field theories or the non-relativistic approaches from quark model implementations. In this work, we employ functional methods within QCD, which contains the toolset of Dyson-Schwinger and Bethe-Salpeter equations. The aim is to extend its successful application beyond the light and strange baryon spectrum, to charmed and bottom baryons. Additionally, we study baryons formed from any flavor combination, from three equally flavored quarks to three different flavored quarks.The work builds upon the quark-diquark Bethe-Salpeter equation (BSE), where the interaction consists of quark exchange between quarks and diquarks, with all components determined from the quark level. This approach simplifies the Faddeev equation, which describes the baryon as a three-body system, to a two-body equation that is numerically solvable. Its solution scheme involves a deeper exploration of the Dirac and flavor terms of the quark-diquark amplitude, and a transformation of its BSE into an eigenvalue problem that can yield, through statistical intrapolation and extrapolation techniques, desirable properties from the ground and excited states of a given baryon. The approach reveals interesting insights into the internal structure of baryons, including non-negligible relativistic components in terms of p-waves, which are typically suppressed in non-relativistic treatments, as well as unequal diquark contributions for a given baryon with different flavored quarks. Current results focus on the 1/2+ and 3/2+ baryon channels as well as 0+ and 1+ diquark channels, meaning that future work is focused on expanding the obtained results beyond these channels.

Unified equation of state probing compact stars
2025-03-12 17:00 - 19:00 | Sala de Formação Avançada do DF (2-8.11) + Zoom (Formato Híbrido)
Meeting ID: 971 1964 8836Passcode Zoom (se necessária): 134631The equation of state (EoS) of neutron stars plays a crucial role in determining their internal composition and observable properties. In this study, we construct an EoS, incorporating a 1st order phase transition from hadronic to quark matter using a Maxwell construction, and apply it for modelling both static and rotating neutron stars. In the quark matter phase, we consider the effects of vector repulsion and color superconductivity, which significantly alter the stiffness of the EoS and the onset of the deconfinement phase transition, respectively.Our results in the static case provide very good agreement with the astrophysical constraints extracted from the gravitational wave (GW) signal GW170817 and even the subsolar-mass compact object HESS J1731-347. For non-vanishing rotational velocities, we compare our outcomes with a collection of measurements of the most recent millisecond pulsar (MSP) measurements and again find consistency with the observational data. Additionally, we developed a model of accretion matter onto rotating hybrid stars with finite magnetic. The model predicts a set of measurable parameters that can be verified by future data.Furthermore, we apply an alternative approach for unified treatment of quark-hadron matter, i.e. the framework of quarkyonic matter. We for the first time introduce the effects of color superconductivity in the quark gluon plasma to the framework of quarkyonic matter. In upcoming publications, we will examine the impact of colour superconductivity in quarkyonic matter and compare it to the Maxwell construction of the 1st order phase transition.

Bridging Theory and Machine Learning: Analytical Insights into Neural Networks and Generative Models
2025-03-13 10:00 - 12:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Modern artificial intelligence has achieved state-of-the-art performance across various domains, from solving protein folding to predicting new materials. However, establishing a solid theoretical foundation for machine learning remains an ongoing research challenge. This seminar explores how analytical models can help bridge this gap.In the first part, we examine the learning behavior of neural networks near their optimal point. Specifically, we analyze the Hessian of the loss function with respect to the learnable parameters in teacher-student setups where both networks share the same architecture. By characterizing the Hessian eigenspectrum for different activation functions, we show that the Hessian rank at the optimal solution effectively determines the number of relevant parameters. In the second part, we discuss recent research on applying generative diffusion models to classical spin systems, such as the Ising model. The Ising model serves as a testbed, allowing us to leverage its well-understood analytical properties to explore how different design choices in diffusion models impact generative performance.

Probing the equation of state of dense matter: neutron-star properties and multi-messenger constraints
2025-03-13 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Neutron stars are unique laboratories to probe matter in extreme conditions that cannot be currently reproduced on Earth. The determination of their equation of state (EoS) is a challenge, but it is particularly important since it allows to relate different global neutron-star properties and to link the prediction of astrophysical observables to microphysical properties of dense matter. In this presentation, I will give a brief introduction on the dense-matter EoS, and specifically on the EoS for neutron stars. Various constraints will be discussed and the prediction of neutron-star observables obtained with a large variety of EoSs by performing Bayesian analyses will be presented in connection with recent (multi-messenger) astrophysical observations.

Simulations of the Einstein-Maxwell system
2025-03-14 16:00 - 18:00 | Online
Electromagnetism plays an important role in a variety of applications in gravity. To that end, in this talk, we present an implementation of the Maxwell equations within the adaptive-mesh pseudospectral numerical relativity code \textsc{bamps}. We present a thorough analysis of the evolution equations as a first order symmetric hyperbolic system of PDEs, including the construction of the characteristic variables for use in our penalty boundary communication scheme, and radiation, constraint preserving outer boundary conditions which, in the language of Kreiss-Agranovich-Metivier, are shown to be boundary-stable. After presenting a formulation of the Maxwell constraints that we may solve for initial data, we move on to present a suite of numerical tests. Our simulations, both within the Cowling approximation, and in full non-linear evolution, demonstrate rapid convergence of error with resolution, as well as consistency with known quasinormal decay rates on the Kerr background. Finally we present evolutions of the electrovacuum equations of motion with strong data, a good representation of typical critical collapse runs.

Development of a Radiation Detection System Coupled to an Unmanned Aerial Vehicle for Security and Defence Applications
2025-03-19 14:00 - 16:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
A deteção e controlo de materiais nucleares especiais (SNM) e substâncias radioativas em setores como a medicina, indústria, ambiente, espaço e a investigação são cruciais para a segurança global e a utilização segura das fontes de radiação. SNM, como o plutónio e o urânio altamente enriquecido, representam riscos significativos, pois podem ser utilizados em dispositivos nucleares improvisados. Além disso, o tráfico ilícito de materiais radioativos levanta preocupações relativamente ao seu potencial uso em dispositivos de dispersão radiológica (e.g., "bombas sujas") e dispositivos de exposição radiológica, com consequências graves e disruptivas. O controlo eficaz das fontes de radiação exige uma supervisão rigorosa durante o transporte, especialmente em postos fronteiriços, aeroportos e portos marítimos. Para tal são normalmente utilizados portais de monitorização de radiação, contudo o seu elevado custo e utilização limitada dificultam a prevenção do tráfico ilícito. A tese descreve o desenvolvimento de um sistema inovador de deteção de radiações, concebido para aplicações de Segurança e Defesa em ambientes caracterizados por grandes distâncias entre a fonte e o detetor e pela presença de fontes ocultas. O sistema utiliza cintiladores EJ-200 e EJ-426HD, com fotomultiplicadores de silício, para detetar simultaneamente radiação gama/beta e neutrões respetivamente. Projetado para veículos aéreos não tripulados (VANTs), oferece um desenho compacto e leve. Validado por simulações de Monte Carlo, testes laboratoriais e de campo, foi capaz de detetar e localizar fontes radioativas de 137Cs (4 MBq) e de 241AmBe (1.45 GBq). A utilização de um novo algoritmo, com planeamento de caminhos informativo e funções custo, aumentou a exatidão na localização e quantificação da fonte, reduzindo igualmente o tempo de inspeção com a utilização de uma condição de saída. O desenho modular, o baixo custo, a integração num VANT e a facilidade de replicação tornam este sistema uma alternativa ou complemento às tecnologias de deteção de radiação existentes.

Nonlinear Relativistic effects in Structure Formation in ΛCDM
2025-03-20 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In this talk I will give an overview of work on nonlinear structure formation in ΛCDM in the context of General Relativity (GR). Starting from briefly presenting a post-Friedmann approximation (similar to post-Minkowski, but on a cosmological background and assuming small peculiar velocities), I will show how at leading order the gravito-magnetic effect (AKA frame-dragging) can be extracted from standard Newtonian N-body simulations, as well as from N-body simulations with GRAMSES, an approximate GR code. In this context, one can conjecture about going beyond-leading order with the aim of computing the gravitational wave background. I will then present full-GR simulations of a toy-model “cosmic web” of over-densities, voids and filaments with the Einstein Toolkit fluid code, showing how the first shell-crossing at peaks of over-densities is very well predicted by the simple "top hat" model, while in the formation of the cosmic web a role is played by gravito-magnetism, especially around filaments. In the last part of the talk I will illustrate some work in progress, some aimed at extending the work on frame-dragging on smaller galactic scales, some aimed at understanding to what extent relativistic effects can play a role during collapse and past the first shall crossing and virialization. I will conclude with an outline of possible future work.

Inteligência Artificial como Catalisador para Inovação em Materiais na Cadeia do Hidrogênio
2025-03-25 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Esta pesquisa investiga a aplicação de inteligência artificial no desenvolvimento denovos materiais para a cadeia do hidrogênio, com foco na criação de membranasavançadas para eletrolisadores. O estudo envolve o desenvolvimento de membranascompostas por quitosana, óxido de grafeno e nanocelulose, visando aprimorar aeficiência e a sustentabilidade na produção de hidrogênio verde. Utilizando técnicas deinteligência artificial, realizamos a caracterização e a otimização do desempenho dessasmembranas, permitindo uma análise mais eficiente dos dados e a identificação depadrões que podem ser explorados para melhorias significativas. Os resultados obtidos demonstram um potencial promissor para o uso dessasmembranas em sistemas de eletrólise, superando as limitações das tecnologiasconvencionais. Além disso, esta pesquisa contribui para o avanço da tecnologianacional, capacitando pesquisadores e fomentando a inovação na área. Ao integrarciência e tecnologia, buscamos soluções energéticas sustentáveis que atendam aosdesafios globais contemporâneos, promovendo um futuro mais verde e eficiente.

ULTRAFAST X-RAYS AND EXTREME PLASMAS
2025-03-26 14:30 - 16:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST

The impact of Artificial Intelligence on precision Higgs Boson physics
2025-03-26 16:00 - 18:00 | Anfiteatro PA1 (Piso -1 do Pavilhão de Matemática) do IST
Particle physics has a long history of developing sophisticated simulators, from modeling proton collisions to creating virtual detectors. Now, we're integrating Artificial Intelligence through "Neural Simulation Based Inference," which helps analyze complex phenomena that cannot be to computed analytically from first principles. This approach is highlighted by recent work from the ATLAS experiment at the Large Hadron Collider at CERN, which has provided new insights into quantum interference in a rare Higgs boson decay. We also touch on how biases ("known unknowns") are modeled, as showcased in the recent Fair Universe HiggsML uncertainty challenge at NeurIPS 2024. Separately, advances in AI generative models, which allow to generate fake images, can be harnessed to emulate particle physics simulators, albeit with specific challenges which will be presented.

Exploring the uncharted Universe with Gravitational Waves
2025-03-27 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Every time that we have looked further into the Universe, we have found fascinating surprises. Most notably, we observe that an omnipresent dark energy drives the Universe to expand ever faster, and that its large-scale structures hold together only because of an invisible dark matter. We do not fully understand how cosmic structures form, and even if our laws of gravity are valid at all scales. Gravitational waves (GWs) – ripples in space and time produced by extreme gravitational systems in the cosmos such as binary black holes – offer a unique opportunity to answer these fundamental open questions. In this talk we will venture into uncharted regions of the Universe and explore how present and future GW observations can test the standard cosmological model. In particular, I will discuss how the population of compact binaries can be used to constrain the expansion rate of the Universe at high-redshift, and how lensed GWs can probe dark matter substructures and shed light on the origin of the observed binary back holes.

Orbital resonances in extreme-mass-ratio inspirals and gravitational wave phenomenology
2025-04-03 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The arrival of next generation space-borne detectors, such as the Laser Interferometer Space Antenna (LISA), will probe uncharted territories of the gravitational Universe and unequivocally strengthen our understanding of the gravitational interaction in multiple directions. In this talk, I will focus on one of the prime targets of LISA, the so-called extreme-mass-ratio inspirals (EMRIs). EMRIs are binaries that consist of a supermassive black hole, such as those lurking in galactic cores, and a stellar-mass companion. I will discuss their rich waveform phenomenology, with a main focus on the effects of orbital resonances, as well as potential gravitational-wave observables that may be detected with LISA.

Axion evidence in the spectrum of open confining strings and the large-NC limit
2025-04-09 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
We compute the spectra of open flux tubes formed between a static quark-antiquark pair for various gauge groups in the large-Nc limit, focusing on different symmetries manifested by the quantum numbers of angular momentum, parity, and charge conjugation.Specifically, we present spectra from Nc = 3 up to Nc = 6 and for eight different irreducible representations of the symmetry characterizing the flux tube. In this study, we employed an anisotropic Wilson action, a large number of suitable spacial operators, and solved the generalized eigenvalue problem (GEVP) to obtain a significant number of excitations for different combinations of flux tube quantum numbers.The spectra are compared with the Nambu-Goto string model, revealing novel phenomena such as the presence of massive axions in the flux tube spectrum. We find that the mass of the axion in the open flux tube spectra sector is consistent with the mass obtained in the closed flux tube sector.

Backreaction of perturbations around a stable Light Ring
2025-04-10 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Light rings (LRs) - closed circular orbits of null geodesics - are key features of both black holes and horizonless ultracompact objects. While unstable LRs are relevant for the observation of black hole images, stable LRs have been suspected to trigger instabilities, namely in exotic compact objects that could mimic black holes. The underlying mechanism behind this instability remains poorly understood, but a key missing piece is how the backreaction of a perturbation around the stable LR modifies the surrounding spacetime. In this talk, some progress in this direction is discussed by examining a conceptually simple, yet instructive, toy model: continuum-shell stars, supported solely by tangential pressures. Using both analytical and numerical methods, we show how perturbations around the stable LR deepen the geodesic potential and shifts its location inward, potentially amplifying any instability associated with the LR. By then extending the analysis to more general stars with nonzero radial pressure, we find that the same phenomenon can be expected to persist under reasonable assumptions.

Study of top quark events in the search for physics beyond the Standard Model at the Large Hadron Collider with the CMS detector
2025-04-15 10:00 - 12:00 | Online
Lepton Flavour Universality (LFU) is a global accidental symmetry of the Standard Model (SM). LFU predicts that all charged leptons must have the same couplings and their only difference must come from the different mass. Tests of this behaviour are of great interest as deviations from this prediction would be a clear signal of New Physics (NP). In this work, a LFU measurement is performed studying the leptonic decays of W bosons in top quark events, including in the final state electrons, muons and taus. An orthogonal method, employing double ratio of different leptonic final states, is used to reduce the impact of systematic uncertainties and improve the precision. Machine Learning techniques are employed in the separation of signal and background events exploiting the large amount of data collected in CMS at the LHC Run2

Probing Physics in the Standard Model and Beyond in gauge boson scattering with the CMS experiment at the Large Hadron Collider
2025-04-15 11:00 - 13:00 | Online
The study of multi-boson production processes is an important test of the standard model (SM). The WW production at hadron colliders is sensitive to the properties of electroweak (EW) boson self-interactions and provides a test of the predictions of perturbative quantum chromodynamics (QCD) and the EW theory. It also constitutes a large background in the measurement of Higgs boson production, as well as in searches for physics beyond the SM. In this work, a measurement of the WW pair production cross section in proton-proton collisions at 13.6 TeV is performed for the first time in a final state that includes a hadronically decaying tau lepton.

Static-light Q̄ Q̄qq potentials for b̄ and c̄ heavy quarks and u, d and s light quarks from lattice QCD. A case study for hadron-hadron interactions
2025-04-16 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
We report on our ongoing lattice QCD computation of antistatic-antistatic potentials in the presence of two light quarks using the CLS 𝑁 𝑓 = 2 gauge configurations and the OpenQ*D codebase. We utilize a set of 16 creation operators, corresponding to 8 sectors characterized by angular momentum and parity quantum numbers for light quarks 𝑞𝑞 = (𝑢𝑑 − 𝑑𝑢)/ 2 (isospin 0), 𝑞𝑞 ∈ {𝑢𝑢, (𝑢𝑑 + 𝑑𝑢)/ 2, 𝑑𝑑} (isospin 1) and 𝑞𝑞∈{𝑢𝑠, 𝑑𝑠} (isospin 1/2 and strangeness −1). We improve on previous work by considering a large number of off-axis separations of the static antiquarks and by using tree-level improvement. The resulting potentials provide vague indication for one-pion exchange at 𝑄¯ 𝑄¯ separations 𝑟 >∼ 0.5 fm. The short stop-motion film “Tetraquarks on the Lattice” by Bernardo Picão will also be presented.

Analogue cosmological particle creation in an ultracold quantum fluid of light
2025-04-24 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The rapid expansion of the early universe resulted in the spontaneous production of cosmological particles, some of which are observable today in the cosmic microwave background anisotropy. We present our observation of the spontaneous creation of analogue cosmological particles in the laboratory, using a quenched 3-dimensional quantum fluid of light. We observe acoustic peaks in the density power spectrum, in close quantitative agreement with the quantum-field theoretical prediction. We find that the long-wavelength particles provide a window to early times. This work introduces the quantum fluid of light, as cold as an atomic Bose-Einstein condensate.

Ultrafast Laser Science
2025-04-29 14:00 - 16:00 | Online
The development of ultrafast laser sources has revolutionized the scientific landscape. Due to their versatility and precisely-controlled properties, these sources are widely used as drivers and diagnostic tools across a broad range of cutting-edge applications. In the last few decades, the mid-infrared region has attracted substantial interest primarily due to its access to molecular vibrational and rotational modes, as well as for its potential for enabling advanced phenomena such as harmonic generation and attosecond pulse generation.We present several experimental efforts at the Laboratory of Intense Lasers (L2I) at Instituto Superior Técnico, with a particular focus on the development of a millijoule-level laser source delivering 3000 nm pulses with a duration of 85 fs at a repetition rate of 10 Hz. This system is based on Chirped Pulse Amplification (CPA) and Optical Parametric Chirped Pulse Amplification (OPCPA).We also discuss the design and numerical simulation of the front-end for the upcoming VULCAN 20-20 project in the United Kingdom aiming for a 20 PW beamline.

Spontaneous Hawking radiation in a sonic black hole
2025-04-30 16:00 - 17:00 | Anfiteatro PA1 (Piso -1 do Pavilhão de Matemática) do IST
Stephen Hawking predicted that black holes should radiate, but observation of this Hawking radiation from a real astrophysical black hole seems unlikely, since the predicted temperature of the radiation is extremely low. Bill Unruh asserted that Hawking radiation might be observable in a sonic black hole, in which sound plays the role of light. We make such an observation in a sonic black hole formed from a Bose-Einstein condensate. We confirm that the Hawking radiation is spontaneous, thermal, and stationary. Furthermore, we follow the time evolution of the Hawking radiation, and compare and contrast it with the predictions for real black holes. We observe the ramp up of the Hawking radiation, similar to a real black hole. The spontaneous Hawking radiation ends, and stimulated Hawking radiation begins, when the sonic black hole forms an inner horizon in addition to the event horizon.

Novel Microelectrode Array Architectures...
2025-05-06 10:00 - 12:00 | Sala 02.1 (Piso -2 do Pavilhão de Civil) do IST
Registos de atividade elétrica em culturas neuronais serão fundamentais para futuros desenvolvimentos médicos, científicos e tecnológicos. Matrizes de microelétrodos (MEAs) são instrumentais em eletrofisiologia, mas são tradicionalmente planares, insuficientes para medir a atividade de culturas 3D, que melhor replicam sistemas in vivo. MEAs 3D ultrapassam esta limitação, geralmente com maior complexidade de fabrico. Nesta tese, múltiplas configurações de MEAs 3D e respetivas estratégias de fabrico são apresentadas, utilizando apenas técnicas de microfabricação convencionais. Elétrodos em forma de cogumelo foram fabricados por eletrodeposição. Matrizes 3D de elétrodos foram obtidas a partir de desenhos 2D, utilizando tensão de filmes finos num material flexível (poliimida). Caracterização com Espetroscopia de Impedância Elétrica e mapeamento de nível de ruído dos elétrodos, garantiu propriedades dos MEAs compatíveis com a aplicação final. Matrizes de elétrodos em forma de cogumelo foram fabricados com sucesso. O protocolo de caracterização estabelece um padrão de comparação entre diferentes camadas de passivação, com Si3N4//SiO2//Si3N4 apresentando o melhor desempenho. A geometria 3D levou a baixo ruído elétrico. MEAs 3D auto-atuados foram conseguidos com 100% das estruturas em poliimida tendo ângulos de 90° em relação ao substrato, mostrando a reprodutibilidade e uniformidade do processo. As matrizes fabricadas têm capacidade de endereçamento em 3D. A validade de ambos os tipos de MEAs 3D foi demonstrada com registos de atividade neuronal. O trabalho aqui apresentado marca um avanço significativo para o fabrico a baixo custo de MEAs 3D de alta precisão. Os dispositivos fabricados nesta tese estão na posição de se tornarem ferramentas indispensáveis no futuro de estudos eletrofisiológicos e neurociência.

On the presence of a fifth force at the Galactic Center: an update with GRAVITY data and future prospects
2025-05-07 11:00 - 13:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In this talk I will present the recent results obtained by the GRAVITY Collaboration on the presence of a Yukawa-like correction to Newtonian gravity at the Galactic Center (GC). The precision of the GRAVITY instrument allowed us to derive the most stringent upper limit for the intensity of the Yukawa contribution (~ α e- λ r) at the GC to be |α| < 0.003 for a scale length λ = 3 x 1013 m (~ 200 AU), improving by roughly one order of magnitude all estimates obtained in the past. I will also show how the inclusion of multiple stars in the fit can help break the degeneracy between both the parameter α, the black hole mass MBH and the PPN parameters γ and β in the large λ limit, when considering specific alternative theories of gravity.

Frontiers of Light Shaping: Nonlinear and High-Power Structured Light
2025-05-08 14:00 - 16:00 | Online

Black Hole Spectroscopy Tools for Waveform Modelling
2025-05-08 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Next-generation gravitational-wave detectors will have enough sensitivity to resolve multiple ringdown frequencies from binary black hole mergers. This requires high-fidelity waveform models to extract as much information as possible from these signals and perform tests of general relativity. In this talk, I will introduce two public tools for extracting the quasinormal mode amplitudes of binary black hole systems: qnmfits, which uses linear least-squares fitting, and NRSurr3dq8_RD, a surrogate model that uses machine learning to predict these amplitudes as well as remnant parameters for areas of parameter space where we lack simulations. With these tools at hand, one can easily build analytical ringdown waveforms.

1-Loop Partition Functions and Schwinger Pair Production in a Near-Horizon Near-Extremal Black Hole Background
2025-05-09 10:00 - 12:00 | Online
Nesta tese estudamos as funções de partição de 1-loop e a produção de pares de Schwinger num espaço-tempo bidimensional de Anti-de Sitter ( ), que surge na vizinhança do horizonte no limite quase-extremal de um buraco negro de Reissner-Nordstrӧm em quatro dimensões espaciais.Este estudo é motivado pelo recente interesse renovado na gravidade de Jackiw-Teitelboim (JT) em duas dimensões, que surge da redução dimensional em uma esfera bidimensional de uma teoria de Einstein-Maxwell em quatro dimensões espaço-temporais, e que serve como um modelo simplificado para a compreensão da gravidade quântica e da física dos buracos negros.Neste contexto, analisamos as trajectórias clássicas de uma partícula escalar num espaço-tempo de buraco negro na presença de um campo elétrico externo constante. Discutimos as simetrias da Lagrangiana da partícula e subsequentemente quantizamos o sistema de partículas. Utilizando o método do kernel de calor e as técnicas da função zeta de caracteres desenvolvidas recentemente na literatura, derivamos a ação efetiva de 1-loop regularizada para uma partícula carregada em Com esta ação efetiva, determinamos a taxa de produção de pares de Schwinger no espaço-tempo do buraco negro quando a intensidade do campo elétrico ultrapassa um limiar crítico.Os nossos resultados demonstram que a taxa de produção de pares de Schwinger num espaço-tempo de buraco negro é igual às obtidas noutros sistemas de coordenadas tais como em coordenadas de Poincaré patch e em coordenadas globais. Esta concordância não é trivial devido ao facto de que esses sistemas de coordenadas estão relacionados por transformações envolvendo a coordenada temporal, resultando em Hamiltonianos diferentes.Adicionalmente, em concordância com estudos anteriores, verificamos que a ação efetiva de 1-loop regularizada possui um termo logarítmico que depende do fator de escala de , semelhante à correção logarítmica da área à entropia de Bekenstein-Hawking de um buraco negro de Reissner-Nordström extremal em quatro dimensões espaço-temporais.No nosso trabalho que submetemos à JHEP, demonstrámos que este termo logarítmico corresponde a um cálculo da entropia de entrelaçamento de fronteira no dual , o qual é identificado como um modelo de mecânica quântica conforme de Alfaro-Fubini-Furlan com acoplamento . Esta computação é realizada através de um estado thermofield duplo no dual Consideramos esta correspondência como uma realização da conjectura de Ryu-Takayanagi em

An overview of plasma-based accelerators and light sources
2025-05-14 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
What is the origin of space, time, and matter? What happens when matter is subject toextreme conditions of pressure and temperature? Can we visualize and control thenano-world? Particle accelerators and light sources have become instrumental inaddressing these long-standing scientific challenges. Because they can sustain muchhigher electric fields than conventional materials, plasmas promise a new generationof more compact, sustainable, and less expensive particle accelerators and lightsources. They are a high research priority in the 2020 update of the European Strategyfor Particle Physics and are being progressively incorporated into the main activities oflarge-scale laser facilities and accelerator laboratories. The intrinsic miniaturization inplasma acceleration brings unique challenges. Addressing them is an essential part ofthe research agenda. These challenges are multidisciplinary, and their solutiondepends on an integrated approach combining theory, simulation, and experimentalphysics. This talk will present an overview of these challenges, along with recentaccomplishments and perspectives for the future of plasma-based accelerators andlight sources for applications in high-energy physics, high-energy density science, andphoton science.

High-intensity and nonlinear structured light
2025-05-14 16:00 - 17:00 | Room EA5 (Mechanics Building I) do IST
High-intensity structured light could one day power the world—provided we figure out laser fusion (an enormous if!) using metasurfaces patterned with tiny, extremely precise nanostructures. Meanwhile, nonlinear structured photonics might unravel the very mystery of life, assuming photons can learn how to spontaneously self-organize into artificial living creatures. Both goals are equally absurd and irresistible. This Colloquium explores these grand ambitions, where the only certainty is that the journey ahead will be nonlinear, intense, and hopefully illuminating.

Nonlinear echoes from black holes in Einstein-Maxwell-scalar theory
2025-05-15 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The post-merger portion of the gravitational wave emitted in a binary coalescence encodes precious information about the structure of the remnant. While in the case of a black hole in General Relativity the signal is described by a standard ringdown, when considering different objects, or alternative theories of gravity, new features might emerge. In this context an interesting possibility is the appearance of echoes. While they are generally studied for exotic compact objects, it has recently been found that they might arise also for black holes in the Einstein-Maxwell-scalar extension to General Relativity. Indeed, in a particular region of the parameter space, this theory admits hairy black hole configurations whose effective potential under scalar or gravitational perturbations features cavity-like structures, where radiation can be trapped and echoes can be generated. In a recent work, carried out in collaboration with Marco Melis, Robin Croft and Paolo Pani, we computed the quasi-normal frequencies of such black hole solutions, for radial and axial modes. Furthermore, by performing simulations of the spherical collapse of scalar wave packets, we have been able to observe the presence of echo patterns in the time-domain behavior of the scalar field, even in the regime where nonlinearities are significant. In this talk I will present the results of our study and discuss our follow-up project, in which we will simulate the head-on collision process with the aim of investigating whether echoes are preserved in such a scenario, or they are quenched by other dynamical effects.

DEVELOPING A TABLETOP X-RAY NANOSCOPE - THE NANOXCAN
2025-05-21 16:00 - 17:00 | Anfiteatro EA5, Torre Norte

Understanding the link between scrape-off layer and pedestal conditions at JET using density profile measurements by reflectometry
2025-05-27 09:30 - 11:00 | Anfiteatro GA1 (Piso 0 do Pavilhão Central) do IST
The confinement of the plasma edge regions, the pedestal and the Scrape-Off Layer (SOL), has a large impact on the stability and efficiency of the entire system but the physics behind them are complex and partly outside first-principles theory. Empirical scaling laws are a crucial tool in understanding these processes, and the JET reflectometer provides a unique opportunity to study the pedestal and SOL, as it has high temporal and spatial resolutions. Methods were developed to process and validate the reflectometer data and to extract and condense each shot to a set of physical parameters. Models that accurately describe all edge profile regions were created and improved. It was found that the density at the end of the high gradient region had a weak correlation with the separatrix density. A large database of shots was created, from which a selection of scans was chosen, to cover a large range of plasma parameters. By studying the parameter correlations in the different scans, it was observed that the SOL confinement improved in the corner configuration and with higher triangularity and plasma current, and degraded with the increase in gas fuelling and heating power. Only triangularity was seen to have a positive impact on the pedestal confinement, with other parameters having a neutral or negative effect. A temporal analysis of Edge Localised Modes (ELMs) was performed on several shots, to analyse the timescales of an ELM and how ELMs are affected by the different parameters. It was observed that the pedestal density has a longer recovery (around 30ms) than both pedestal and SOL widths (around 5ms). It was also seen that in certain conditions ELMs can have a long tail, associated with a period with near-constant values of pedestal width and gradient, and a larger energy loss than normal ELMs. The largest impact of the plasma parameters on ELMs was found to be the ELM shape and timescale. Increased gas fuelling also showed a reduced impact of ELMs on the profile.

Probing EFT Wilson Coefficients in the Wtb vertex at the HL-LHC
2025-05-27 14:00 - 16:00 | Online
O vértice Wtb, central para a fenomenologia do quark top, oferece uma oportunidade única para investigar possíveis extensões do Modelo Padrão, particularmente no contexto da Teoria de Campo Efectiva (EFT).Este trabalho apresenta uma projecção abrangente para a fase de alta luminosidade do LHC (HL-LHC) das restrições sobre os operadores de dimensão 6 da EFT que afectam a interação Wtb, utilizando uma análise global que incorpora simultaneamente múltiplos observáveis, incluindo secções eficazes de produção de um único quark top, fracções de helicidade do bosão W e assimetrias angulares, em vários modos de produção e decaimento do quark top. Uma nova metodologia de ajuste é implementada para tratar os coeficientes de Wilson de forma consistente, evitando suposições simplificadoras frequentemente presentes em abordagens tradicionais. Os resultados mostram que, embora as sensibilidades projectadas sejam comparáveis aos limites experimentais actuais, essa melhoria modesta levanta questões quanto à justificação das expectativas em torno do HL-LHC e sublinha a necessidade de metodologias mais gerais e rigorosas.Este trabalho demonstra que ajustes globais podem produzir limites mais conservadores, mas mais robustos, e questiona algumas das premissas adoptadas nas estratégias de análise predominantes.

Física Experimental de Partículas: da instrumentação e deteção à aprendizagem automática
2025-05-28 15:00 - 16:00 | Anfiteatro Abreu Faro
As experiências modernas em física experimental de partículas usam tecnologias de ponta em deteção de partículas aos últimos avanços em métodos de análise de dados para obter informações sobre as propriedades das partículas elementares e das suas interações. Neste seminário, Inês Ochôa e Rute Pedro irão falar da interação entre instrumentação e aprendizagem automática na experiências ATLAS no LHC/CERN, passando das tecnologias de deteção e das operações às tomadas de dados e suas análises. Nesta viagem irão também explorar o panorama dos aceleradores para além do LHC e discutir as lições aprendidas para o desenho e construção de futuras experiências.

Cosmic Accelerators: Unraveling Nature's Most Extreme Engines
2025-05-28 16:00 - 18:00 | Room EA5 (Mechanics Building I)
From black hole jets to shock waves from exploding stars, the universe hosts natural particle accelerators that reach energies far beyond anything built on Earth, glowing across the entire electromagnetic spectrum. Yet how these cosmic engines actually work remains a long-standing mystery. In the XPACE project, we combine advanced numerical simulations with novel laboratory experiments—using the world's most powerful lasers—to recreate extreme astrophysical conditions. These efforts are offering new insights into how plasmas become remarkably efficient particle accelerators, helping to unravel the physics behind some of the universe's most energetic and fascinating phenomena.

Fix the Frame, Resolve the Memory: The Bondi--Sachs Gauge in Black Hole Perturbation Theory
2025-05-29 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Understanding gauge and frame dependence is crucial for comparing binary models and extracting physical observables. Black hole perturbation theory calculations are extending to second-order, where increased gauge dependence brings new challenges: gauge-invariant quantities at linear order become gauge-dependent at second-order, and nonlinear source terms can produce infrared divergences. Additionally, gravitational wave memory, a frame-dependent effect, appears at second order and will be detectable with next-generation detectors. In this seminar, I review second-order black hole perturbation theory, the Bondi--Sachs gauge, the BMS frame, and memory effects; by combining these elements, I construct a gauge invariant second-order field equation associated with an asymptotically flat gauge with the appropriate frame to extract the memory.

Particles for Health: Improving Radiotherapy
2025-06-04 16:00 - 17:00 | Anfiteatro EA5, Torre Norte
Radiotherapy is a standard treatment for cancer, using energy beams--most commonly photons--to destroy malignant cells. While conventional radiotherapy is well established, significant efforts are underway to improve its efficacy through advanced techniques originating from Particle and Nuclear Physics.One such approach involves the use of ultra-intense beams to trigger the FLASH effect, which has been shown in several studies to increase the sparing of healthy tissue. However, clinical implementation of this technique presents challenges in beam monitoring, control, and safety. Promising solutions to these challenges may be drawn from instrumentation developed in particle and astroparticle physics experiments.Another major development is the rise of theranostic tools--techniques that combine therapy and diagnostics using the same treatment beam. An example is the EU-funded BoneOscopy project, which aims to assess treatment efficacy by detecting by-products of proton radiotherapy. This talk will present the goals of the project, its main challenges, and some of the proposed solutions.

Atomic processes in XFEL-driven plasmas
2025-06-05 10:00 - 12:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Over the past two decades, X-ray free-electron lasers (XFELs) have made significant progress, achieving peak brightness X-ray regions that were previously only attainable in the infrared. This has opened new possibilities in high-energy density science, enabling the creation of solid-density plasmas with larger volumes and better uniformity. XFEL heating proceeds through photoionisation and thermalisation, initially creating non-thermal electron distributions, offering a new platform for generating plasmas with tailored properties.We investigate the effects of inelastic thermalisation in iron under intense X-ray irradiation using the atomic model BigBarT, which evolves the electron distribution self-consistently. Our study focuses on collisional M-shell ionisation, identified as the most efficient relaxation mechanism for non-thermal electrons. This could impact high-energy electron transport and points to the relevance of including atomic processes in kinetic models. Comparing calculated spectra with experimental data may also help refine collisional cross sections, which are challenging to compute due to screening and continuum effects. We also report the observation of the shake-off process in solid-density XFEL-produced plasmas. Titanium foils were irradiated with XFEL pulses at 5.1 and 6 keV. Emission spectra show satellite features only at the higher energy, consistent with the threshold for simultaneous K- and L-shell ionisation. These signatures are absent at lower energies and cannot be explained by standard collisional or Auger ionisation mechanisms.

The making and testing of spin-2 ULDM galaxies
2025-06-05 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Ultra-light dark matter (ULDM) is a compelling and phenomenologically rich candidate for the cosmological dark matter. ULDM is typically considered to be a (pseudo)scalar or a vector field, but even more interesting and unique physics can be realised for spin-2 tensor fields. In this talk I will review how spin-2 dark matter arises from the only known consistent modification of gravity to include multiple spin-2 fields, and discuss (a) how the ULDM spin changes the properties of idealised haloes obtained through isolated soliton mergers, (b) how to detect spin-2 ULDM using pulsar-timing data, in particular how to detect perturbations in binary systems with machine-learning techniques, and (c) how to detect spin-2 ULDM with gravitational wave interferometers, with an emphasis on existing LIGO/Virgo data.

Data-driven modeling of collisional kinetic plasma dynamics
2025-06-09 16:00 - 18:00 | Online
Computational plasma physics has seen significant advances in the ability to model nonlinear plasma dynamics from first-principles. However, capturing the complex multi-scale dynamics of plasmas, especially in non-equilibrium and strongly coupled regimes, remains challenging. This talk will highlight recent work that explores the potential of combining machine learning algorithms with traditional plasma kinetic simulation frameworks to address these challenges.The first part of the talk will focus on integrating Graph Neural Networks (GNNs) as surrogate models for kinetic plasma simulators. We demonstrate that GNNs can accurately replicate the dynamics of a one-dimensional plasma for arbitrary degrees of collisionality, and generalize effectively to conditions well beyond their training data. We also show that GNNs can implicitly learn a computationally efficient collisional operator in 1D. In the second part, we discuss the use of self-consistent electromagnetic Particle-in-Cell (PIC) simulations that resolve the inter particle fields that mediate collisional interactions to guide the development of data-driven, collisional operators. These data-driven operators can shed light on the nature of collisions in strongly coupled regimes and, in the future, elucidate how collisional operators are modified in far-from-thermodynamic-equilibrium conditions.

Black Holes and Gravitational Waves as Probes of New Physics
2025-06-11 16:00 - 17:00 | Room EA5 (Mechanics Building I)
The past decade has witnessed a revolution in gravitational-wave (GW) astronomy. Since the first GW detection by LIGO and Virgo a decade ago, observations of black hole and neutron star mergers have become routine, offering new ways to test general relativity and explore extreme astrophysical environments. But these discoveries may just be the beginning. As we look ahead, a new generation of GW detectors, both ground-based and spaceborne, promises dramatic improvements in sensitivity and event rates, opening doors to deeper insights into fundamental physics. In this colloquium, I will explore an exciting frontier at the intersection of gravitational-wave science and particle physics: the use of black holes and GWs to search for ultra-light bosonic particles beyond the Standard Model. I will outline the basic physical mechanisms that make this possible and highlight recent theoretical and observational developments. This emerging synergy between astrophysics and particle physics may provide a unique window into the dark sectors of our universe.

Memory and tail effects for interacting scalar fields
2025-06-12 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Interactions and self-interactions of nearly massless scalar fields can be relevant to both dark matter and dark energy. Here we use the Schwinger-Keldysh approach to the effective field theory of a binary system coupled to a scalar field to analyse memory effects along hyperbolic orbits or tail effects and their consequences for the dynamics of the binary system.

Quantum Avalanches and Krylov-space integrals of motion in disordered systems
2025-06-18 14:30 - 16:00 | Anfiteatro PA2 (Piso -1 do Pavilhão de Matemática) do IST
Anderson localization is a phenomenon in which a single quantum particle's eigenstates are exponentially localized due to spatial disorder. This begs the question of whether a disordered interacting system can be similarly localized, a phenomenon dubbed many-body localization (MBL). Thermalization in the thermodynamic is believed to be due to ''quantum avalanches'', in which rare Griffiths regions serve as thermalizing baths. These regions, which are sure to exist in the thermodynamic limit, are rare by nature and thus to observe their effect one either needs to access very large system sizes or resort to biased sampling. In this talk we present evidence of avalanches in numerical studies using the latter, and show these systems are unstable at disorder much larger than commonly believed (Physical Review B 108 (2), L020201). We will also briefly review the Krylov subspace expansion method as a probe of quantum chaos and the existence of localized integrals of motion (LIOMs) in Krylov space.

Electrically charged hyperboloidal evolution
2025-06-23 14:00 - 16:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online
Password: [REDACTED] present the Einstein-Maxwell-Klein-Gordon system in hyperboloidal slices, a recent formulation for extracting signals at future null infinity. As far as we know, this is the first time this setup is evolved with a common formulation like BSSN/Z4. Using hyperboloidal slices, contrary to other recent methods like Cauchy-Characteristic Matching, we can continuously reach future null infinity. With this system, we simulate how a charged scalar field behaves in flat spacetime and near a charged black hole. We are further able to see the scalar field's quasi-normal modes and analyze the late-time power-law tail decays. Both phenomena were tested to see how they change with the electromagnetic coupling between the black hole and the charged scalar field. A comparison of previously studied analytical results to our simulations is shown. We also showcase the collapse of the charged scalar field into a Reissner-Nördstrom black hole.

Numerical hyperboloidal compactification: waves on FLRW and neutron star initial data
2025-06-24 11:00 - 13:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Both parts of this talk involve numerical descriptions on compactified hyperboloidal slices reaching future null infinity -- the "location" in spacetime where electromagnetic and gravitational radiation arrives and where global properties of spacetimes can be measured. The first part, presenting joint work with Flavio Rossetti, focuses on the asymptotic decay of the linear wave equation on flat and hyperbolic FLRW spacetimes with a time-dependent scale factor. I will describe the hyperboloidal setup, which allows us to recover decay rates obtained from evolutions on usual truncated Cauchy slices, and also consider solutions of a non-linear wave with self-interactions. The second part will describe the construction of initial data for a neutron star on a hyperboloidal slice, involving spherical symmetry and a polytropic-like equation of state. Constraint-satisfying compactified hyperboloidal initial data are obtained for a single neutron star and for a combination of a neutron star with a small black hole in its center. To the best of my knowledge, this is the first time that full hyperboloidal slices including a neutron star are constructed.

Extreme mass-ratio inspirals into bosonic stars
2025-06-24 14:00 - 16:00 | Online
Password: [REDACTED] Campos bosónicos massivos podem formar estruturas solitónicas autogravitantes: estrelas de bosões no caso de campos escalares e estrelas Proca no caso de campos vetoriais. Para campos ultraleves, estas estruturas podem descrever os núcleos de matéria escura que envolvem buracos negros supermassivos no centro das galáxias. Tem sido argumentado que futuros detetores de ondas gravitacionais poderão ser capazes de sondar as propriedades de estruturas compostas por matéria escura. Neste trabalho, estudamos estrelas de bosões e estrelas Proca esfericamente simétricas, bem como estrelas Proca axialmente simétricas, no regime Newtoniano. Aplicamos teoria linear de perturbações a todas as configurações e calculamos os modos quasinormais para os casos esfericamente simétricos. As frequências obtidas são puramente reais, o que indica a presença de modos normais e ausência de instabilidades neste regime. Analisamos de seguida a resposta de cada configuração à presença de um pequeno objeto compacto em espiral em direção ao centro da estrela. Por fim, calculamos a perda total de energia do objeto, comparando-a entre as diferentes classes de solitões. Os resultados mostram que a resposta da estrutura bosónica depende da natureza do campo e constituem um primeiro passo rumo a uma descrição totalmente relativista.

Muon Energy Spectrum from the Analysis of Inclined Shower Footprint
2025-06-25 15:00 - 17:00 | Sala V0.04 (Piso 0 do Pavilhão de Civil) do IST/
Raios cósmicos de energia extrema atingem a atmosfera e geram chuveiros atmosféricos extensos com energias inalcançáveis pelo Large Hadron Collider. O número de muões detectados ao nível do solo é um observável fundamental para determinar a composição em massa do primário. Porém, medições de longa duração mostram que os modelos existentes de interação hadrónica preveem sistematicamente menos muões do que os observados — discrepância conhecida como o Extensive Air Shower Muon Puzzle. Além disso, o espectro de energia dos muões não é consistente entre diferentes modelos de interacção hadrónica em altas energias. Neste trabalho, exploramos a deflexão provocada pelo campo magnético terrestre para avaliar o espectro de energia dos muões. Após determinar a configuração do campo geomagnético que produz a maior separação entre muões positivos e negativos provenientes de chuveiros extensos de 80 graus, introduzimos e investigamos uma variável, a Muon Azimuthal Distribution, que caracteriza a forma da pegada de muões no solo. O estudo centra-se em muões com energias de 10 GeV, 100 GeV e 1 TeV, analisando como as suas trajectórias e distribuição espacial final são afectadas pelos principais mecanismos físicos e geométricos envolvidos no desenvolvimento do chuveiro. Para isolar e compreender a contribuição de cada efeito, realizámos simulações que incorporam o impacto de mecanismos individuais — como o espalhamento Coulombiano e múltiplo, processos de decaimento, e subsequentemente, o conjunto combinado de processos electromagnéticos. Em seguida, alargámos a análise considerando diferentes altitudes de produção dos muões, examinando como as distribuições azimutais resultantes evoluem através das camadas de altitude. Finalmente, usando o espectro de energia dos muões para atribuir pesos adequados às distribuições correspondentes a cada energia e profundidade de produção, obtivemos uma Muon Azimuthal Distribution representativa para o espectro considerado. Este resultado fornece novas pistas para resolver o espectro de energia dos muões em altas energias para diferentes modelos de interacção hadrónica.

Numerical studies of Hawking radiation via hyperboloidal slices
2025-06-25 16:00 - 18:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online
A criação de partículas a partir do vácuo devido à geometria do espaço-tempo é uma previsão fundamental da Teoria Quântica dos Campos em espaços-tempo curvos. No entanto, a simulação de campos quânticos em espaços-tempo dinâmicos, como os que correspondem ao colapso gravitacional, é computacionalmente complexo. Para explorar este fenómeno, esta tese desenvolve um modelo simplificado: um campo quântico escalar evoluindo numa métrica de Minkowski fixa, com a presença de um potencial dependente do tempo que induz a dinâmica necessária para a criação de partículas. O método envolve evoluções em fatias hiperboloidais - hipersuperfícies space-like que atingem assimptoticamente o infinito nulo - num espaço-tempo que fixa o infinito nulo numa localização de coordenadas finitas na grelha computacional. A criação de partículas é analisada pelo cálculo dos coeficientes de Bogoliubov e , em que diferentes de zero significam criação de partículas. O modelo investiga dois cenários estacionários (sem potencial e potencial estático) e dois casos dinâmicos, em que a amplitude ou o centro do potencial mudam harmonicamente no tempo. Os cenários estacionários revelam negligenciáveis - duas ordens de magnitude abaixo dos coeficientes - enquanto os cenários dinâmicos demonstram criação de partículas, com coeficientes da mesma ordem de grandeza que os . Todos os resultados da simulação apresentam, no geral, boa convergência e satisfazem a condição de normalização . Os resultados comprovam a utilidade das fatias hiperboloidais para o estudo numérico de criação de partículas e a análise necessária para assegurar resultados fiáveis e normalizados.

A global approach to the nonlinear perturbation of a black hole by gravitational waves
2025-06-26 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
It is well known that gravitational waves interact in a nonlinear way. This makes it difficult to describe them rigorously. The cleanest description is based on certain conformal properties of the Einstein equations — first discovered by R. Penrose, they were rigorously developed and used by H. Friedrich to prove several important global results for general relativistic space-times. The conformal field equations, which implement this conformal framework, provide various well-posed initial (boundary) value problems for use in many different situations. The talk will give a computational perspective on one particular application, the non-linear interaction of gravitational waves with an initially static (and spherically symmetric) black hole. We will show how to 'kick' the black hole and possibly how to spin it up.

Kinetic instabilities in bidimensional Dirac materials
2025-06-27 11:00 - 13:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online
A plasmónica em materias bidimensionais revelou-se uma área de estudo ativa, e estes sistemas mostram potencial para serem usados como futuros dispositivos optoelétricos para um grande número de aplicações de alta frequência.Apesar do modelo hidrodinâmico estar bem estudado na literatura, para ir além do regime de alto comprimento de onda e equilíbrio local, um modelo cinético é utilizado. De forma a incluír correções quânticas importantes à dinâmica das partículas condutoras, este modelo é derivado a partir da equação de Schrödinger, através da função de quasiprobabilidade de Wigner em campo médio.Um código de simulação numérica é desenvolvido, com capacidade para simular sistemas cinéticos com larga generalidade, incluindo os efeitos de estatística quântica, estrutura de bandas de diferentes materiais, bem como interações inter-partículas arbitrárias. Este código é paralelizado para uso em simulações de grande escala com alto desempenho.Usando este modelo com aproximações apropriadas como ponto de partida, bem como as simulações para estudar fenómenos não lineares, várias ondas e instabilidades são descritas. No caso de campos estáticos, a frequência e tempo de vida de plasmões é derivado, e o comportamento da instabilidade de fluxo duplo em duas dimensões, que leva a uma resistividade anómala sem colisões, é encontrado.Descrevemos também o não confinamento de ondas eletromagnéticas transversas nestes materiais, mas encontramos uma instabilidade relacionada que gera espontaneamente campos magnéticos com direção perpendicular ao plano.Finalmente, uma similar instabilidade de agregação com frequência zero num sistema de partículas repulsivas é mostrado.

Sensitivity of the ATLAS Experiment to Beyond the Standard Model Higgs Interactions in the H->bbgamma Decay
2025-07-01 09:30 - 12:00 | Online
The Standard Model (SM) leaves key phenomena unexplained, motivating searches for physics beyond the SM (BSM). Probing the Higgs sector may reveal insight into new physics. This thesis aims at determining the ATLAS experiment sensitivity to the rare Higgs decay H→bbγ, a process not yet experimentally observed. BSM effects in the Hbbγ interaction are parametrised via Effective Field Theory, where non-zero anomalous couplings modify its cross-section and may enhance sensitivity to the decay. The analysis is performed in the context of the LHC High-Luminosity phase, using Monte Carlo simulations at sqrt(s)=14 TeV, with an integrated luminosity of 3000 fb^-1 and considering pile-up effects. The decay was studied through the Higgs and W associated production, resulting in a final state with one charged lepton, two b-jets, and a photon. Pre-selection cuts based on the final state are applied to prepare the data for multivariate analysis. Two deep neural network classifiers are trained using different training datasets. The first method trains solely on the SM signal and background, while the second is trained with combined SM and BSM signal data, plus background. The second method presents better performance overall and is used to estimate the expected signal significance. The results indicate lower sensitivity compared to earlier literature results obtained in similar studies due to the inclusion of more extensive background contributions and pile-up effects. The evidence of a BSM signal can only be reached for large values of the BSM couplings, close to today's exclusion limits. The study concludes that full detector simulation with detailed pile-up modelling must be performed to design future strategies to deal with the dominant backgrounds of soft and fake photons.

Learning Dynamics of Neural Networks
2025-07-02 16:30 - 18:00 | Anfiteatro QA1.2, Piso 1, Pavilhão de Química, Campus Alameda
This thesis investigates the learning dynamics of neural networks through a combination of statistical mechanical and dynamical systems tools, within the controlled setting of the teacher–student framework. We use this setup by introducing a minimal student model trained to reproduce the outputs of a fixed teacher network via Stochastic Gradient Descent on a mean-squared error loss. By analyzing the Hessian of the loss function, we characterize the local curvature of the landscape at and near optimal points, revealing how overparameterization and activation function choice shape the spectrum of eigenvalues and, hence, the rates of convergence. To probe transient chaotic behavior during training, we compute Local Lyapunov Spectra and observe that, even in low-dimensional teacher-student tasks, there is local chaoticity that can theoretically lead to exponentially diverging parameter trajectories before they settle into stable minima or flat manifolds. Principal Component Analysis of these trajectories further uncovers a marked reduction in effective dimensionality over the course of training, with the majority of variance confined to leading modes that coincide with directions of minimal curvature in the Hessian. Finally, when extending our framework to a network learning from a dataset on the MNIST classification task, we find that entropy measures derived from positive Local Lyapunov Exponents do not correlate with generalization performance, highlighting the need for alternative complexity metrics in realistic, high-dimensional settings.

Optimization of the local reconstruction in a high granular calorimeter using a heterogenous computing model
2025-07-03 10:00 - 12:00 | Online
Password: [REDACTED] High-Luminosity phase of the Large Hadron Collider (HL-LHC) at the European Organisation for Nuclear Research (CERN) will deliver an unprecedented dataset of proton-proton collisions at the highest centre-of-mass energies to date. With over 140 simultaneous interactions per bunch crossing and luminosity of around 1034 cmâˆ’2 sâˆ’1 , both the CMS detector and its computing infrastructure face significant challenges. These include severe radiation damage, high particle fluxes, and the need for fast and precise reconstruction to isolate physics signals of interest, particularly for precision measurements. To meet these demands, the CMS experiment is undergoing major upgrades, including the replacement of the endcap calorimeters with a high-granularity sampling calorimeter (HGCAL). HGCAL will provide combined energy and time measurements from approximately six million channels, enabling accurate particle flow reconstruction under extreme pileup. The upgrade features a silicon-based sampling structure with fine spatial segmentation, enhancing both spatial and temporal resolution. This thesis explores the development and validation of a local reconstruction and calibration framework using data from HGCAL beam tests. A key contribution is an automated method to extract the most probable value (MPV) of energy deposits from minimum ionising particles (MIP) across individual silicon sensors, a critical step in calorimeter energy calibration. Essential processing steps include pedestal subtraction, noise correction, and timing alignment. The calibration algorithms were tested and validated under real beam test conditions. This work contributes to a per-channel calibration method that will be essential for the accurate calibration of HGCAL in preparation for its deployment in the HL-LHC era.

Pulsar Timing Arrays: a window into dark matter and gravity
2025-07-03 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Pulsar Timing Array (PTA) facilities are powerful experiments timing an ensemble of galactic millisecond pulsars and have recently reported strong evidence of a stochastic gravitational wave background, most likely originating from inspiraling supermassive black hole binaries. While a primary objective is to characterize this signal and the underlying population of astrophysical sources, PTAs also offer a unique window into fundamental physics. In this talk, I will demonstrate how PTAs can probe two distinct aspects of fundamental physics: on the one hand, the nature of dark matter, including its interactions with the Standard Model and its gravitational coupling; on the other hand, modified theories of gravity that influence the inspiral of supermassive black hole binaries.

dentifying Inequalities in Information Diffusion on Social Media: A Study of Twitter Cascades Across User, Content, and Contextual Groups
2025-07-03 15:00 - 17:00 | Online
How do user, content, and contextual characteristics influence the growth of cascades on social media? In this study, we address this question by analysing over 1.9 million tweets their corresponding retweets to investigate how user characteristics (e.g., gender, country, verification status, number of followers), content veracity (e.g., true and false), and contextual factors (namely the time of day) influence diffusion dynamics. We model cascade growth using an analytical function with two parameters (initial diffusion rate and diffusion decay rate and assess their distributions using the Generalised Gamma Distribution (GGD), a flexible family of distributions that can adapt its shape through parameter tuning to represent a wide range of known distributional forms, including heavy-tailed behaviours. Group-based comparisons reveal clear asymmetries: male users, verified accounts, and users with many followers tend to initiate larger cascades, while female and unknown-gender users show statistically equivalent patterns. Although the size distribution of true claims exhibited heavier tails, indicating the presence of some very large cascades, veracity did not significantly increase the expected number of retweets when controlling for other factors in a regression model. Simulations based on fitted parameters successfully replicated the overall cascade distribution but failed to reproduce differences between groups, likely due to the use of a fixed network structure. Regression models for cascade size confirmed the strong influence of user visibility and verification. However, the models explaining the initial diffusion rate and diffusion decay rate accounted for only a small proportion of their variance. This suggests that the dynamics of initial growth and subsequent slowdown of cascades are less predictable based on user, content, and contextual features alone, and may be influenced by other unobserved variables.Our findings highlight how differences in exposure, engagement, and social perception can contribute to biases in information diffusion (especially along gender and visibility lines), offering a basis for future studies in algorithmic fairness and platform governance.

“Measurement of the polarizations of prompt and nonprompt J/ψ and ψ(2S) mesons produced in pp collisions at √s = 13 TeV
2025-07-04 09:30 - 11:00 | Sala 02.1 do Centro de Congressos (Piso -2 do Pavilhão de Civil) do IST
Quantum Chromodynamics (QCD) is the sector of the Standard Model responsible for describing interactions between quarks and gluons. Because of the unique nature, within the Standard Model, of its coupling constant, calculations in QCD remain a challenge. Quarkonia, bound states of a heavy quark and its respective antiquark, are the simplest case study for hadron formation processes, and so are the ideal probes for a better understanding of QCD. In this thesis, we study one of the fundamental properties of quarkonium states, their polarization, characterized experimentally by the angular distribution of their decay products. Using data samples collected by the CMS experiment in 2017 and 2018, corresponding to a total integrated luminosity of 103.3 fb−1 , we measure the polarizations of prompt and non-prompt J/ψ and ψ(2S) mesons produced in proton-proton collisions at √ s = 13 TeV, using the dimuon decay channel. The polar anisotropy parameter in the helicity frame, λ HX ϑ , is measured as a function of the transverse momentum, pT, of the two charmonium states, in the 25–120 GeV range for the J/ψ and in the 20–100 GeV range for the ψ(2S). The measurements are compared with predictions. The non-prompt polarizations agree with predictions based on the hypothesis that, above a pT of around 25 GeV, these states are predominantly produced in two-body B meson decays. The prompt results definitively exclude the theory expectation of strong transverse polarizations (λϑ =+1) for the pT range under study, which exceeds 30 times the J/ψ mass, as λϑ tends to an asymptotic value around 0.3 over this range. Taken together with previous LHC measurements for √ s = 7 TeV, compatible in the overlap pT region, the prompt λϑ shows a significant variation with pT, at low pT.

Temporal Phenotyping of ALS Patients using Machine Learning
2025-07-04 12:00 - 14:00 | Online
Password: [REDACTED] Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by highly heterogeneous and rapidly progressing motor decline. Despite extensive research, predicting ALS progression remains a major clinical challenge, limiting timely interventions such as Non-Invasive Ventilation (NIV) and Percutaneous Endoscopic Gastrostomy (PEG). This thesis addresses this challenge by applying machine learning (ML)-based temporal phenotyping to characterize evolving patient profiles from static and longitudinal clinical data, with the objective of uncovering distinct progression trajectories and improving prognosis prediction.Specifically, the T-Phenotype algorithm is adapted to the Lisbon ALS Clinic dataset, leveraging phenotypic predictive clustering to group patients by both outcome and disease trajectory similarities. Comprehensive preprocessing strategies were developed to handle irregular clinical event timing, missing data, variable-length time series, and class imbalance. The algorithm identified clinically meaningful phenotypes associated with the need for NIV (endpoint C1) and PEG (endpoint C3), with optimal performance in shorter observation windows (6–12 months), revealing distinct risk profiles aligned with respiratory and bulbar function decline. Combining endpoints into a multiclass task (C1+C3) highlighted challenges with class imbalance and reduced prediction performance, although still produced interpretable phenotypes. Temporal analysis of cluster transitions illustrated the model’s ability to capture diverse ALS progression patterns dynamically, emphasizing the disease's heterogeneity and the limitations of static classifications. Although the T-Phenotype model had satisfactory results in predictive accuracy and clustering interpretability for the binary endpoints (Hprc metric around 80%), its performance declined for the combined endpoint (Hprc metric around 65%), its performance declined for the combined endpoint. Additionally, it lacked sensitivity to clinical improvements post-intervention, underscoring the need for richer datasets and methodological rigor.The potential of ML-based temporal phenotyping was demonstrated as a valuable tool for understanding ALS progression and supporting personalized prognosis and intervention planning. By integrating temporal dynamics into patient stratification, this approach advances data-driven ALS monitoring and highlights critical considerations for future research in this domain.

Design and validation of microfluidic structures on a Lab-on-a-CD for biomedical diagnosis
2025-07-07 16:00 - 18:00 | Anfiteatro QA1.1, Piso 1, Pavilhão de Química, Campus Alameda
Microfluidic devices are crucial in biomedical research, enabling precise manipulation of small fluid volumes for diagnostics and drug delivery. Advances in materials and fabrication techniques have sig- nificantly improved their performance. This thesis focuses on developing and optimizing a pneumatic siphon in a microfluidic system using advanced thermoplastics and precise CNC milling.Polymethyl Methacrylate (PMMA) was chosen for its optical clarity, strength, and cost-effectiveness, ideal for microfluidic applications. Initial designs were crafted in AutoCAD and refined with 3D modeling and simulations in Fusion 360, ensuring meticulous tool selection and parameter optimization. The primary challenge was achieving accurate fluid flow and priming within the pneumatic siphon.The main result of this research was the valuable learning curve associated with microfluidic design and manufacturing. This study underscores the importance of iterative testing and precise engineering in microfluidic device development, revealing that practical adjustments are often needed for optimal performance. The research validates PMMA and advanced CAD/CAM tools in microfluidic fabrication, emphasizing the need for continuous refinement in design processes.In a broader context, this study contributes to a methodology for pneumatic structures design and optimization, enhancing microfluidic system reliability and efficiency for scientific and medical applica- tions. This work highlights the critical role of material selection, precise engineering, and iterative testing in advancing microfluidic technologies, providing insights applicable across various disciplines.

Neural posterior estimation for gravitational-wave inference
2025-07-10 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
I will describe how deep learning and simulation-based inference address gravitational-wave data analysis challenges, including high event rates and rapid electromagnetic follow-up. The approach uses simulated data to train neural networks, such as normalizing flows, to accurately represent posterior distributions. Once trained, these models enable extremely rapid inference—reducing analyses to seconds. I will highlight recent advances in population inference and binary neutron star parameter estimation, demonstrating the promise of these techniques for next-generation detectors.

Evaluating the radiation chemistry of Flash radiotherapy via Monte Carlo simulations
2025-07-14 10:00 - 12:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
Flash radiotherapy is an emerging cancer treatment that employs ultra-high dose rates to enhance tumor control while significantly reducing damage to healthy tissue, compared to conventional radiotherapy. This differential tissue response is known as the Flash effect, and its underlying mechanism remains unknown. It has been hypothesized that increased radical-radical reactions might potentially correlate with the Flash effect, as these could substantially affect the indirect DNA damage. During my PhD I developed an innovative multiple pulse extension for gMicroMC, a Monte Carlo track-structure algorithm, to explore the impact of dose rate on radical-radical reactions. I validated the model against external algorithms and pulse radiolysis experimental data. I conducted simulations of multiple pulse irradiations, which indicated a dose rate threshold. Below this threshold, a steady-state in the concentration of species was consistently maintained within every pulse, resulting in a constant postirradiation chemical yield. In contrast, above the threshold, the high pulse frequency prevented the achievement of the steady-state, leading to an accumulation of reactive species throughout the irradaition. This reactive species build-up significantly promoted radical-radical reactions, increasing the post-irradiation yield of hydrogen peroxide. This phenomenon is more likely to boost radical-radical reactions compared to the inter-track mechanism.

From Data to Membranes: Predicting Performance and Guiding Material Selection with Machine Learning
2025-07-16 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The integration of machine learning (ML) techniques into membrane research offerspromising possibilities for accelerating material discovery and enhancing processperformance prediction. In this talk, I will first provide a brief motivation for the use ofML in membrane development, followed by an overview of key ML concepts andcommon methods for regression and classification tasks. Two case studies willillustrate the practical application of these tools. The first explores the use of ML topredict gas permeability in polymeric membranes and leverages these predictions toidentify promising new materials for gas separation. The second applies ML models intwo different tasks: to identify and estimate the distribution of pores, and to forecastthe long-term performance of membranes used in membrane distillation processes,offering a data-driven approach to system monitoring and optimization. Theseexamples highlight how ML can complement experimental efforts and supportdecision-making in membrane research.

Thermodynamics and statistical mechanical ensembles of black holes and self-gravitating matter
2025-07-22 11:00 - 13:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
Black holes exist all over our Universe, possessing a very wide range of masses. At the moment, they serve as a probe to test general relativity at astrophysical scales, but in the future they may also give us information about gravity at the microscale. Black holes seem to have thermodynamic properties, such as the Bekenstein-Hawking entropy, which are important when considering black holes with size of a few centimeters or smaller. Since entropy in statistical mechanics is related to the number of possible microstates of a system, several questions arise: what gives rise to the black hole entropy? Can it be explained by a quantum description of gravity? In order to further study these questions, the connection between thermodynamics and gravity must be explored at the microscale. In this doctoral thesis, we aim to understand this connection using two descriptions that yield the thermodynamics of curved spacetimes. We start by imposing the first law of thermodynamics to a charged self-gravitating matter thin shell in higher dimensions. The fundamental pressure equation of state can be used for the shell, which is given solely by general relativity. An equation of state for temperature of the shell is also chosen, so that it allows the study of the black hole limit and the recovery of black hole thermodynamics. Furthermore, we use the Euclidean path integral approach to quantum gravity to construct statistical ensembles of black hole spacetimes and self-gravitating matter, in order to study semiclassically the possible phase transitions between hot matter and black holes. We also show the power of the formalism in obtaining the thermodynamic properties of curved spacetimes. Namely, we study the canonical and grand canonical ensemble of charged black holes inside a cavity, which may have a finite or infinite radius. We also construct ensembles of a self-gravitating matter thin shell, both in anti-de Sitter and in asymptotically flat spaces, in order to understand the thermodynamic features of the shell and the possible phase transitions to black hole configurations.

YOLO Application on Portuguese Highways for Photovoltaic Energy Potential Evaluation
2025-07-25 14:30 - 16:00 | Online
The global push for renewable energy has accelerated the deployment of photovoltaic (PV) systems, raising concerns about land availability and competition with other land uses. A promising solution lies in repurposing underutilised highway infrastructure, such as sound barriers and excavation slopes, for PV installations. This thesis investigates the application of computer vision, specifically the YOLOv10 object detection algorithm, to automatically identify these structures along highways using video and image data. The methodology proposed in this work, which combines object detection with geolocation, enables the estimation of electric energy generation and supports the technical-economic assessment of the viability of these infrastructures for renewable energy production.For sound barriers, several YOLOv10 models were trained on progressively larger datasets, improving mAP@0.5 from 0.57 to 0.90. The geolocation method developed, based on the synchronisation of GoPro videos with GPS data, makes it possible to map detected barriers and estimate their solar potential. In a case study involving 64 sound barriers, two PV installation scenarios were evaluated, achieving energy yields of 17.8 kWh/kW and 27.7 kWh/kW per barrier. These results compare favourably with similar projects in Europe, confirming the strong solar potential in Portugal.Excavation slopes are visually more complex structures and harder to identify. Despite using a modest dataset, the model was still able to successfully detect these types of infrastructure, achieving a mAP@0.5 of 0.54. The case study showed that these slopes could generate between 88 and 170 kWh/year per m2, depending on their orientation.

Self-Similar Collapse in Spherically Symmetric Elasticity
2025-09-09 14:00 - 16:00 | Sala de Seminários do Departamento de Física (2-8.3 - 2º Piso do Edíficio de Física)/Online
Perfect fluids have been widely used in the simulation of realistic astrophysical phenomena, such as collapse and binary coalescence. Nevertheless, these fluid models are very simple and their use to describe the full extension of a compact object, from core to envelope, may not be adequate and leave out more complex aspects of stellar dynamics. Elastic matter models generalize perfect fluids by also taking into account deviations from a relaxed state and, furthermore, allow for a smooth matching at separation surfaces. Thus, elasticity can be used to model compact objects with complex compositions.Despite showing promise, there are few results using elasticity. To this end we studied this matter model in the context of self-similar spherically symmetric gravitational collapse. Self-similarity pertains to systems displaying invariance with regards to scale changes. In the context of collapse it provides two advantages. On the one hand, the description of the system depends only on the scale variable, removing the need to solve PDEs, while still retaining many properties of collapse. On the other hand, self-similarity is closely linked with critical collapse, the study and understanding of collapse at the threshold of black hole formation and associated processes.In this talk I will go over the results obtained for self-similar collapse. I will show how elasticity compares with perfect fluid models, and how the tuning of the material parameters affects the spacetime through the material's response to the collapse, specifically in the generalization of the well known Evans-Coleman solution, as well as in the case of other modes of collapse. I will also show how the material's characteristics affect the regularity of the spacetime, and how they may forbid the existence of self-similarity altogether.

“Kinetic Instabilities in Extreme Plasma Physics: Laboratory and astrophysical dynamics
2025-09-09 16:00 - 18:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática) do IST
Extreme plasma physics explores regimes where strong electromagnetic fields, intense radiation, and quantum electrodynamics (QED) effects fundamentally alter the behavior of matter. These conditions are found in some of the most energetic astrophysical environments, such as pulsars, black holes, and relativistic shocks, and are increasingly accessible in laboratory experiments using high-intensity lasers and particle beams. This Thesis investigates how radiation reaction, through synchrotron and betatron cooling, reshapes phase space and triggers kinetic instabilities across a range of such extreme plasma conditions.First, we show that synchrotron cooling in strongly magnetized plasmas generically leads to anisotropic, ringshaped momentum distributions that are unstable to the electron cyclotron maser instability (ECMI). Radiation reaction sustains population inversion and enables prolonged coherent emission beyond classical saturation. Second, we demonstrate that betatron radiation in plasma wakefields produces similar structuring in high-energy beams, forming "donut beams"" with pitch-angle anisotropies. These features are confirmed through analytical theory and largescale three-dimensional simulations. Finally, simulations in the context of the Fireball experiment at CERN demonstrate how relativistic electron-positron beams develop collective instabilities under realistic laboratory conditions, providing the first direct analogues of astrophysical pair-plasma dynamics. Together, these studies represent two interconnected threads of extreme plasma physics, radiative cooling and pair-plasma kinetics, and lay the groundwork for a kinetic theory of radiatively structured plasmas, bridging theory, simulation, and experiment, and opening new paths toward probing high-energy astrophysical processes in the laboratory

Constraining Multi-scalars models with colliders and Dark Matter
2025-09-17 09:30 - 11:00 | Sala 02.1 do Centro de Congressos (Piso -2 do Pavilhão de Civil) do IST
After the observation in 2012 of a new scalar particle closely resembling the Higgs boson of the Standard Model of particle physics, there is a general consensus that there must be Physics Beyond the Standard Model, with present experiments now dedicated to its discovery. Extending the scalar sector is motivated by key unresolved issues in particle physics including the need of new sources of Charge Parity violation, providing an explanation of the baryon asymmetry in the universe, or to explain Dark Matter, which comprises of order 85% of the matter content of the Universe. In this thesis, we focus on three Higgs doublets models (3HDM) and the constraints that need to be imposed. We add theoretical contributions for the consistency of the scalar potential, with boundedness from below and the global minimum. We consider all constraints for full phenomenological studies in models with different symmetries, studying their individual impact and attempting to distinguish the models based on data. We propose a model with Charge Parity violating coefficients, leading to Higgs couplings that significantly deviate from Standard Model values and remain allowed. To explore the parameter space of the model, we employ an efficient Machine Learning algorithm that finds new regions of parameter space and observable consequences, not found with previous techniques we developed and applied. The new techniques are applicable to any Physics Beyond the Standard Model scenario. We connect the scalar extensions with experimentally viable solutions to the Dark Matter problem. When building Dark Matter models, one often imposes conserved discrete symmetries to stabilize DM candidates. We consider a possibility with two DM candidates, and an alternative possibility of a conserved non-Abelian group leading to a viable DM, in an attempt to chart the limits of what Multi-Higgs Models can accommodate.

Gravitational data analysis with machine learning and deep learning
2025-09-18 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Gravitational-wave astronomy enables precision studies of compact binary systems and provides powerful tests of General Relativity. Black-hole spectroscopy—the detection of gravitational-wave emission spectra from black-hole ringdowns—offers a particularly clean framework for testing gravity theories against well-defined predictions. However, accurate waveform modeling and efficient parameter estimation are essential to extract both astrophysical and fundamental physics insights from the data. In this talk, I will present my recent works in gravitational waveform modeling and inference, with a focus on black hole ringdowns, and highlighting the role of machine learning and deep learning techniques. In particular, I will discuss the promises and challenges of using Gaussian Process Regression for waveform modeling and hierarchical inference, and simulation-based inference for parameter estimation.

Time-axial gauge qcd on a quantum computer
2025-09-24 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Non-perturbative QCD phenomenology is typically investigated using Monte Carlomethods that rely on averaging over static bosonic field configurations. However,these methods break down in the presence of a finite baryon density (chemicalpotential) or when simulating real-time dynamics. Such situations arise, for instance,in the fragmentation of quarks into hadrons or in the physics of neutron-star cores.Quantum computing offers promising new avenues to address these difficulties — ifscalable architectures become available — but they face intrinsic complexities such usthe trade-off between a dense encoding of the relevant degrees of freedom and anefficient decomposition of the resulting unitary transformations. In this talk, wepresent a novel register-based encoding of canonically quantized QCD in the timeaxial / Weyl gauge. We detail the implementation of key Hamiltonian terms anddemonstrate small-scale simulations that provide a preliminary assessment of thecomputational time and memory resources required.

Dark Matter in Compact Stars
2025-09-25 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Compact stellar objects are promising cosmic laboratories to test fundamental interactions, in particular they could shed light on the nature of dark matter (DM). DM captured by the strong gravitational field of these stellar remnants transfers kinetic energy to the star during the collision. This together with further DM annihilation in the stellar interior can have various observational consequences such as the anomalous heating of old compact stars and compact star destruction for non-annihilating DM. We have improved former calculations of the capture and thermalization rates in both white dwarfs (WDs) and neutron stars (NSs), making little approximations about the physics of compact stars. While DM deposits its kinetic energy in the star quite quickly, for appreciable annihilation heating to be achieved, capture and annihilation processes should reach a state of equilibrium. We also revisit the calculation of the capture-annihilation equilibrium timescales in neutron stars. For NSs, we show that capture-annihilation equilibrium, and hence maximal annihilation heating, can be achieved without complete thermalization of the captured dark matter for all types of dark matter - baryon interactions. This includes cases where the scattering or annihilation cross sections are momentum or velocity suppressed in the non-relativistic limit. For scattering cross sections that saturate the capture rate, we find that capture-annihilation equilibrium is typically reached on a timescale of less than a year for vector interactions and 10 thousand years for scalar interactions. For fermionic non-annihilating heavy DM, we also revisit black hole (BH) formation, accretion, and evaporation. We find that previous results on the DM-nucleon scattering cross section for a NS to be destructed by a BH from accumulated DM can be relaxed by a few orders of magnitude.

Astrophysical Probes of Axion Like Particles: insights from Black holes, Galaxies and GW background
2025-09-26 11:00 - 13:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In this talk, I will present three studies exploring observable signatures of axion-like particles (ALPs) in different astrophysical environments. First, I will discuss photon–ALP conversion near the photon sphere of the supermassive black hole M87*, enabled by its surrounding magnetic fields. This process can lead to a dimming of the photon ring, whose sensitivity to ALP mass and coupling opens up an observational window. Second, I will present constraints on eV-scale ALP dark matter derived from infrared to ultraviolet (IR–UV) observations of M87, using multi-instrument data from telescopes. Finally, I will turn to supermassive black hole binaries, showing how their inspirals in the presence of ultralight dark matter through soliton formation in the galactic cores, can imprint signatures on the stochastic gravitational wave background. I will demonstrate how PTA may probe self-interaction properties of ultralight dark matter.

Magnetoresistive Stacks with Improved Thermal Resilience
2025-09-26 14:00 - 16:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
Magnetic sensors are widely used in state-of-the-art electronics and play a crucial role in industrial applications. These sensors act as transducers between magnetic fields and electrical currents and are required to have exceptional performance even in harsh environments. The design of each thin film component is essential to ensure that these technologies remain competitive for next-generation applications. The unidirectional reference of the sensors is typically established through exchange coupling in antiferromagnetic/ferromagnetic bilayers. This work explores the use of two different antiferromagnets (MnIr and MnNi) to enhance the thermal stability of tunnel magnetoresistive devices. The growth conditions and the seed layers (Ta, Ru, CuN), were modified to produce thermally stable structures compatible with operation in harsh environments. Additionally, the stability of tunnel magnetoresistive sensorsto magnetic fields was analyzed for applications as angular sensors. Different synthetic antiferromagnets were studied, along with their impact on the angular performance of the devices. Magnetic anisotropies and interlayer couplings were investigated using a macrospin model, which allowed the definition of material limits to minimize device output errors. Subsequently, the electrical characterization of microfabricated sensors contributed to the understanding of the operational limits and verification the applicability of the developed model. Finally, this work explored a new way to tune the linear range of magnetic sensors (anisotropic and tunnel magnetoresistive sensors) using magnetic antidot structures. When applied to the ferromagnetic layers of the sensors, this methodology enabled the control to the linear region of such devices and modifications to their sensitivity at device/wafer level. This work demonstrates several strategies that can be used to improve spintronic sensing technologies and extend their operational limits. The results are shown to leverage the design of robust sensors targeting harsh environment applications.

Roof-shaped nematogens with optimummolecular biaxiality -A new avenue towards the real thermotropic biaxial nematic phase ?
2025-09-29 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Recently roof-shaped nematogens 1 with an anthraquinone core were identified to approach anoptimum biaxial aspect ratio.[1,2] While biaxial aggregates of hundreds of nematogens have beendemonstrated by NMR relaxometry, the macroscopically aligned biaxial nematic could not beenconfirmed to date. This is a common challenge encountered already in two intense research periods,during which several claims about the discovery of the thermotropic biaxial nematic phase of a lowmolar mass material have been opposed.[3]The present contribution highlights the study of a number of roof-shaped molecules such as 1 and 2 with a slightly distinct substitution pattern. Combined comprehensive X-ray scattering and solid-state NMR investigations reveal that only one of these nematic materials (1) shows a pronounced local interdigitation of the lateral chain along the minor director. This is realised by the long lateral chains pointing towards the anthraquinone core. The self-assembly mechanism enhances the local biaxial order in the nematic phase and impacts on the XRS order parameters of biaxial nematogens 1 and 2. The local freezing of the rotation about the molecular long axis is a prerequisite to find the delicate thermotropic biaxial nematic phase. Fréedericksz transitions of the nematic phases are studied in the presence of electric and magnetic fields to probe phase biaxiality.

Enhancement of QED Processes Using Spatiotemporaly-Shaped Pulses
2025-10-01 15:30 - 17:00 | Sala P9 (2º Piso do Edifício de Matemática)
Recent developments in high-power laser physics have unlocked the possibility of prolific electron-positron pair creation in the laboratory when colliding with an ultrarelativistic electron beam. This is a valuable asset for future particle accelerators and colliders, as the outgoing relativistic beam of positrons can be achieved within a few microns in length, significantly reducing the cost associated with the experimental setup. It is also of great importance to probe the Strong Field Quantum Electrodynamics regime directly, of which few observations have been made thus far.However, any application of such beams requires some level of control or tailoring over their characteristics. Specifically, control over the two dynamical variables a lepton has, momentum and spin, is of great importance for future applications. While separating positrons from electrons can be conventionally achieved, it requires a strong external magnetic field. Such a field causes the spin to precess further, compromising the final degree of polarization of the particles.In this talk, I will show how electromagnetic field asymmetries control the outgoing particles. I will demonstrate how using the asymmetric vector potential of a bichromatic laser pulse can be used to achieve the separation of electrons from positrons after they leave the vicinity of the laser. Additionally, using circularly polarized harmonics, the particles can also acquire spin polarization, leading to a separated and polarized beam of positrons.

Sequential simulation-based inference for extreme mass ratio inspirals
2025-10-02 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Extreme mass ratio inspirals are a key target for next generation space-based gravitational wave detectors because they have a rich phenomenology that could offer new astrophysics and fundamental physics insights. However, their dynamics are complicated to model, and they will be buried amongst a large population of other sources in the milliHertz frequency band, with a background of non-stationary and non-Gaussian noise. Searching for these systems and measuring their parameters therefore presents a difficult challenge.Simulation-based inference methods could offer solutions to some of these challenges. I will show parameter estimation results for extreme mass ratio inspiral systems achieved using sequential simulation-based inference, specifically truncated marginal neural ratio estimation. I will highlight the benefits of this approach with respect to traditional likelihood-based methods, and discuss the broader context in which such a pipeline will need to be embedded as well as how and when environmental effects should be considered.

Structured laser-plasma interactions at ultra-high intensities
2025-10-03 10:00 - 12:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
Laser-plasma interactions at ultra-high intensities provide a powerful platform for accelerating charged particles to high energies (10s−100sMeV) over microscopic distances, offering a promising alternative to conventional accelerators. High-energy protons and electrons play a crucial role in applications such as microscopy, advanced radiation sources, medical treatments, and high-energy-density physics. Advances in laser technology enable the generation of structured beams beyond Gaussian profiles at ultra-high intensities. Tailored phase, polarization, and spatiotemporal coupling introduce new degrees of freedom to manipulate plasma dynamics. This thesis employs theoretical modeling and three-dimensional particle-in-cell simulations to investigate the role of structured lasers in unlocking novel mechanisms for compact particle accelerators. The first objective is to generate collimated high-energy proton beams. We explore effects such as reduced relativistic self-focusing through advanced target designs and support experimental findings on twisted laser-driven proton acceleration, bridging theory, simulations, and experiments. Furthermore, we examine angular momentum gain in plasma electrons under different conditions. We identify a mechanism in which local pump depletion of a laser with azimuthal polarization—but no net angular momentum—facilitates electron rotation. Additionally, angular momentum transfer from lasers carrying spin and orbital angular momentum is analyzed across different plasma regimes, demonstrating their role in generating substantial magnetic fields.

Inflation, the Standard Model Higgs and the nature of gravity
2025-10-03 15:00 - 17:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
This thesis aims to explore aspects of the inflationary and post-inflationary dynamics in the Higgs and Higgs-dilaton inflation models embedded in the framework of Einstein–Cartan gravity. For Higgs inflation, we consider a class of simplified Einstein–Cartan scenarios and employ lattice simulations in 3+1 dimensions to demonstrate that contrary to the metric and Palatini cases, the postinflationary evolution leads to the formation of localized oscillons that produce a stochastic gravitational wave background and induce a period of matter domination. We then perform a complementary analysis to determine their lifetimes. By approximating the oscillons as spherical, we extract their radial profiles and carry out 1+1-dimensional simulations to establish the rate at which they lose energy. Our findings show that self-interactions at low field values cause the oscillons to emit radiation from their outer layers, significantly reducing their lifetimes compared to what is typically found in the literature. We then use these results to refine predictions for inflationary observables, as well as for the amplitude and peak frequency of the gravitational wave signal generated by oscillons. For the Higgs–dilaton model, we focus on the separate effects of a non-minimal coupling to the Holst and Nieh–Yan terms. In this scenario, the inflationary observables are determined by the pole structure of the inflaton kinetic term in the Einstein frame and, for a large portion of the parameter space, are related to the field-space curvature. For the Nieh–Yan case, we find two distinct attractor solutions correlated with the value of one of the dilaton couplings. Besides the known attractor tied to the field-space curvature, we discover a novel attractor induced by a cubic pole in the kinetic term, and whose predictions are consistent with the latest cosmological observations.

Magnetic sensors with superior performance: materials and design optimization for angular sensing
2025-10-03 16:00 - 18:00 | Online
This thesis presents the optimization of magnetoresistive sensors based on magnetic tunnel junctions (MTJs) for high-precision angular sensing. The work combines numerical modeling, material design, and experimental validation to develop sensors capable of achieving sub-degree angular accuracy with improved linearity and thermal stability. A macrospin Stoner–Wohlfarth simulation framework was implemented to evaluate how magnetic anisotropies, interlayer coupling, and geometry influence sensor behavior. These simulations guided the design of optimized MTJ multilayers and led to the adoption of a Wheatstone bridge configuration with orthogonal reference layers to suppress non-linearities in the output signal.Prototypes were fabricated using standard microfabrication techniques and characterized under rotational magnetic fields and controlled temperature conditions. The results show that the bridge-based configuration produces a near-sinusoidal output over 360° with angular deviation limited to ±2.5°, representing a tenfold improvement over single-element sensors. The calculated angular error profile closely matches the experimental measurements, confirming the validity of the model and indicating that residual error arises from physical asymmetries in the device.Thermal stability was investigated through annealing experiments and modeled using a grain-level thermal activation approach. The exchange-bias field was observed to degrade substantially at temperatures above 140°C, in agreement with calculation results. These findings underscore the importance of material selection and stack engineering—such as buffer layer optimization and the use of high blocking-temperature antiferromagnets—for stable high-temperature operation.Overall, the combination of simulation and experimental methods has enabled the development of a angular sensor with improved performance. The findings provide insight into the physical mechanisms that govern angle accuracy and establish a foundation for future sensors that combine high resolution with thermal robustness for demanding industrial and scientific applications.Link

História da música em Portugal
2025-10-06 16:00 - 18:00 | VA5
Desde a criação da disciplina Arte, Tecnologia e Produção Musical, oferecida pelo DF, o Professor Rui Vieira Nery dá anualmente uma aula de 2 h sobre História da Música em Portugal. Para além dos alunos inscritos, alguns colegas (não apenas do DF) têm demonstrado interesse em assistir a essa aula em cada ano.Dado o sucesso dessa aula, o Professor João Seixas decidiu abrir a aula aos alunos e docentes do DF que desejem assistir, dentro da capacidade da sala. Ela terá lugar no anfiteatro VA5 na próxima 2ª feira 6 de Outubro a partir das 16:00.São por isso convidados a vir ouvir o maior musicólogo português da actualidade. Verdadeiramente a não perder.

Detecting scalar fields with EMRIs: the effects of gravitational post-adiabatic corrections
2025-10-09 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Asymmetric binaries, i.e. compact binary systems with a large mass asymmetry, such as Extreme Mass Ratio Inspirals (EMRIs), are key sources for the future space detector LISA. Inspiralling around the central black hole (the primary), the smaller object (the secondary) generates gravitational waves (GWs) that harbour the potential for precise tests of fundamental physics. In this talk, I will focus on a model of asymmetric binaries in theories of gravity with new fundamental scalar fields, where the primary scalar charge per unit mass is suppressed, so that the background spacetime is simply described by the Kerr metric. Moreover, at leading - adiabatic - order in the binary mass ratio, the imprint of the scalar field on the emitted waveform is fully captured by an extra parameter: the scalar charge per unit mass carried by the secondary. I will show how this parameter affects the emitted GWs and, by analysing such signals, I will present the encouraging results on the LISA ability to detect the scalar charge. Finally, I will present the latest results arising from the inclusion of post-adiabatic corrections in the gravitational sector, and discuss their impact on the scalar field detectability.

Investigation of Plasma Thermal Spray Coatings at OGMA: Addressing Delamination Issues in Aerospace Components
2025-10-14 10:00 - 12:00 | Sala P3, Piso 1, Pavilhão de Matemática, Campus Alameda
Atmospheric Plasma Spraying (APS) processes are widely employed in the aerospace industry to enhance thermal resistance and durability of critical components. Despite proven advantages, delamination remains a recurring defect, particularly at coated surface edges where interfacial bonding becomes susceptible to irregularities, contamination, and residual stresses. This phenomenon compromises component qualification for service, increasing costs and reducing reliability. This thesis investigates mechanisms leading to delamination in APS systems and proposes corrective and preventive strategies to mitigate its occurrence. The study combines industrial data analysis, experimental trials, and microstructural evaluations to identify key process variables associated with non-conformities, including interface contamination, roughness non-uniformity, and coating thickness variations beyond specification limits. Statistical analysis of OGMA’s quality control data reveals delamination rates correlating with specific process parameter deviations, particularly surface preparation inconsistencies. The research analyzed 165 metallographic and mechanical test reports from over 1,363 OGMA records, revealing a 12.1% nonconformity rate with coating thickness deviations representing 38% of failures. The METCO 450NS + XPT268 combination demonstrated highest delamination risk, with 72% of tensile strength failures correlating with oxide cluster presence. Recommendations include improving surface preparation through frequent abrasive media replacement, controlling roughness uniformity via profilometry, and minimizing material excess using micrometer-based thickness verification. Future proposals encompass robotic automation of surface treatment and predictive quality systems based on in-situ diagnostics. This work, conducted in collaboration with OGMA – Industria Aeron ´ autica de Portugal, S.A., contributes to optimiz- ´ ing plasma spray practices while supporting more sustainable and cost-efficient production frameworks that reduce defect rates and enhance operational lifespan of aerospace components.

Neutron stars as dark matter probes
2025-10-15 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Compact stars, due to their enormous gravitational field, can accumulate a sizable amount of dark matter in their interior. Depending on its nature, accumulated dark matter may affect the properties of neutron stars in quite different ways. I will give an overview of the impact of dark matter on various observable properties of neutron stars, i.e., the mass-radius relation, tidal deformability, merger dynamics, gravitational waveform, thermal evolution, etc. For two scenarios, asymmetric fermionic and bosonic dark matter, the conditions under which dark matter particles tend to condense in the core of the star or create an extended halo will be presented. I will show how dark matter condensed in a core tends to decrease the total gravitational mass and tidal deformability compared to a pure baryonic star, which appears as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo has the opposite effect, causing an increase in those observable quantities. Thus, observational data on compact stars could be affected by accumulated dark matter and, consequently, constraints we put on the strongly interacting matter at high densities. While neutron stars provide a compelling testing ground for gravity, nuclear physics, and physics beyond the Standard Model, the possible degeneracy between the effect of dark matter or gravity beyond GR and dense matter properties could lead to misleading conclusions while analyzing the observational data. We will discuss how the joint efforts of multi-messenger observations of neutron stars, along with experimental and theoretical subatomic physics, are pivotal for breaking a possible degeneracy and shedding light on the neutron star internal composition. In addition, I will review the effect of dark matter on binary neutron star mergers and emitted gravitational wave signals. I will present the numerical-relativity simulations of compact stars admixed with the dark matter component and discuss how the present and next-generation gravitational wave telescopes could shed light on dark matter-admixed compact stars and constrain the dark matter properties.

Beyond the Standard Model: New Perspectives
2025-10-15 16:00 - 18:00 | Anfiteatro PA2 (Piso -1 do Pavilhão de Matemática) do IST
The Standard Model of particle physics, while providing an excellent description of experimental data, leaves key observations unexplained, most notably the existence of dark matter. It also raises deep theoretical puzzles, such as the instability of the Higgs mass in the presence of heavy physics. As conventional solutions to these problems have not emerged at the expected energy scales, it is now crucial to rethink our approach towards physics beyond the Standard Model (BSM). This talk gathers my latest efforts to explore BSM beyond the standard paradigm.In the first part, I will revisit long-standing expectations for new physics near the electroweak scale. I will show that non-minimal versions of traditional models can point to novel and unexplored regions of parameter space, while maintaining their original purpose. I will also discuss novel strategies based on effective field theory to probe more exotic origins of the Higgs boson. In the second part, I will turn to BSM scenarios characterized by more feeble interactions. I will discuss novel aspects of QCD axion phenomenology arising from its interplay with additional scalar fields, which reshape the landscape of axion dark matter searches.Throughout the talk, I will emphasize the importance of refining the map between data and a given particle physics model, to fully explore the unprecedent data which will be gathered by future collider and astrophysical experiments.

Applied SUSY QFT & BHPT: one loop corrections to near extremal (dS-)Kerr thermodynamics
2025-10-16 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The study of Black-Hole perturbation theory [BHPT] is a classical problem in General Relativity and crucial to study gravitational waves. As the high order of symmetry of the BH gravitational field implies separation of variables, BHPT reduces to the study of 2nd order linear ordinary differential equations (ODE). These ODEs have particular rational potentials and are solved exactly by classical Virasoro conformal blocks. The latter have an explicit expression because of AGT duality (BPS sector in susy gauge theory ≡CFT2) and the classical limit of crossing relations generate the explicit solution of the connection problem of the ODE. Applying the solution back to BHPT one gets a powerful computational technique. Quantitative and qualitative (exact) results in BHPT have been obtained so far, such as grey-body factors, Love numbers, quasi-normal modes, BH scattering amplitudes, effective actions in BH backgrounds. In particular, combining with a generalisation of the Gelfand-Yaglom formula for singular potentials one gets an exact expression for the one loop (dS-)Kerr effective action. The latter is shown to undergo a precise scaling with the temperature and proves a conjecture made by means of qualitative arguments on one-loop corrections to the entropy.

Gravitational Symmetry Breaking, the Higgs and the Cosmos
2025-10-23 11:00 - 13:00 | Sala 02.1 do Centro de Congressos (Piso -2 do Pavilhão de Civil) do IST
A non-minimal interaction between scalar fields and the spacetime curvature is a natural and expected occurrence at the high energies characterising the early Universe. For a spectator field, the time-dependence of the Ricci scalar provides a cosmic clock capable of triggering an out-ofequilibrium phase transition as the Universe evolves from inflation to kination. In the present thesis, we explore the cosmological consequences of the so-called Hubble-induced phase transition and its possible observable signatures. We first discuss the case of a prototypical scalar field non-minimally coupled to curvature during a phase of kination following inflation. Its exponentially-amplified fluctuations lead to copious particle production while also generating a stochastic gravitational-wave background peaked at high frequencies. We perform hundreds of fully-fledged numerical lattice simulations in 3+1 dimensions to obtain a detailed understanding of the non-linear and nonperturbative aspects of the system. From the numerical data, we compute a set of parametric formulas that encode several key quantities related to the heating stage and the gravitational-wave spectrum, such as typical energy-densities, timescales, heating temperatures, amplitudes and shape of the gravitational-wave spectrum. Second, we examine the case of the non-minimally-coupled Higgs field undergoing a Hubble-induced phase transition. The negative running of the Higgs selfcoupling leads to the famous vacuum stability problem, which can be avoided by setting a constraint on low-scale particle-physics measurements of the top quark pole mass as well as high-energy cosmological parameters. If stability is assured, the Higgs can undergo a violent process of nonperturbative particle production which heats the post-inflationary Universe into a Standard-Model plasma before big bang nucleosynthesis. A characteristic gravitational-wave signal is associated to the phase transition, which offers a new window into the high-scale behaviour of the Higgs effective potential, including possible new-physics effects.

Timing gravity with pulsars in the strong field
2025-10-23 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The centre of the Milky Way has been subject of an intense observational program over the past thirty years. This led to the discovery of a point source supermassive object named Sagittarius A* (Sgr A*) whose inferred mass is ~ 4 million solar masses. Thanks to the precise tracking of the motion of stars in its surroundings and the direct imaging of accreting matter in this region, we can now unambiguously identify this object as a supermassive black-hole (SMBH). A promising possibility to reach new experimental frontiers in black hole physics is the existence of detectable pulsars on tight relativistic orbits in the Galactic Center. While, up to date, no pulsar has been directly observed in orbit around Sgr A*, future observing facilities like the Square Kilometer Array (SKA) promise not only to reach this goal, but also to be able to perform timing analysis of such sources. In this talk I will show the recent progress in the modeling of pulsar timing in the Galactic Center and the avenues that the successful detection of a pulsar in this environment would open for unparalleled tests of gravity.

Inspiral-merger-ringdown waveforms from gravitational self-force theory
2025-10-30 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Compact binaries with asymmetric mass ratios are key expected sources for next-generation gravitational-wave detectors. Gravitational self-force theory has been successful in producing post-adiabatic waveforms that describe the quasicircular inspiral around a nonspinning black hole with sub-radian accuracy, in remarkable agreement with numerical relativity simulations. These models are based on a two-stage process, which makes waveform generation very efficient: in a (slow) offline stage, waveform ingredients are pre-computed as functions on the orbital phase space; in a (fast) online stage, the waveform is generated by evolving through the phase space. Current inspiral models, however, break down at the innermost stable circular orbit (ISCO), missing the final merger and ringdown stages. In this talk, I will show how the inspiral’s “phase-space” approach can be extended beyond the ISCO, building first-principles inspiral-merger-ringdown waveforms within self-force theory, and I will compare these waveforms with a self-consistently calculated sum over quasinormal modes at late times. Finally, I will briefly discuss how beyond-GR effects can be modularly added in this framework. Based on arXiv:2405.00170, 2506.02189 and 2510.11793.

Real-Time Beam Monitoring Device based on Cherenkov Effect for FLASH Radiotherapy Charged Particle Beams
2025-11-03 11:00 - 13:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online
A major barrier to the clinical implementation of FLASH Radiotherapy (FLASH-RT) is the lack of real-time beam monitoring. Conventional ionization chambers, the current standard, suffer from saturation and slow response times under ultra-high dose rate (UHDR) conditions. To address this limitation, we propose a novel Cherenkov-based beam monitoring chamber specifically designed for FLASH-RT. Cherenkov emission is prompt (sub-nanosecond), linearly proportional to the number of beam particles and free from saturation effects. Our design replaces traditional ionization chambers with a thin in-beam Cherenkov radiator coupled to fast photodetectors. This configuration enables real-time monitoring of FLASH beams with sub-microsecond temporal resolution and no saturation effects. In this thesis, we review the current state-of-the-art in beam monitoring technologies. We established a theoretical framework to assess key characteristics of our device, including the expected signal intensity and its potential impact on the beam. These results were further developed using Geant4 simulations. We expect our device has no saturation effects, minimal beam perturbation and sub-microsecond temporal resolution.

Probing unification scenarios with Big Bang Nucleosynthesis
2025-11-04 15:00 - 17:00 | Sala P3, Piso 1, Pavilhão de Matemática, Campus Alameda/Online
Big Bang Nucleosynthesis (BBN) is an observational cornerstone of the Hot Big Bang model and a sensitive probe of physics beyond it. Although some analytic approximations can be made, a fully consistent analysis must be done numerically, starting with the classic code by Kawano and leading to the recently developed PRyMordial, a publicly available Python code.An example of physics beyond the standard model to which BBN is sensitive are Grand Unified Theory (GUT) models. A self-consistent perturbative analysis of the effects of variations in nature’s fundamental constants, unavoidable in a broad class of GUT models, has recently been developed, and describes the relevant variations with only three parameters: (∆α_EM)/α_EM , R and S.The specific goal of this work is to implement this perturbative approach in the PRyMordial code and use the extended code to obtain constraints on the variations of the abovementioned fundamental constants using current observations.Two different viable scenarios were found, and the three parameters were constrained independently for both cases. The variation of the gravitational coupling can be implemented by varying either particle masses, or Newton’s gravitational constant.With the variation of masses, we obtained a 1σ interval of [-4.89×10^(-5),5.22×10^(-5)] for (∆α_EM)/α_EM and a ratio S/R=2.53±0.06 correlating with the observational values of Helium-4 and Deuterium abundances.For the variation of G_N, we obtained one (R,S) point (-1.52,-6.06) that works best for any (∆α_EM)/α_EM , constraining each of the three in a 1σ interval: [-2.00×10^(-5),2.33×10^(-5) ] for ∆(∆α_EM)/α_EM , [-15.7,16.2] for R, and [-127.3,135.4] for S.

Towards AntiMatter-based Nuclear Reactor Tomography and Beyond
2025-11-05 16:00 - 18:00 | Anfiteatro PA1 (Piso -1 do Pavilhão de Matemática) do IST
Since the discovery of the neutrino in 1956, reactor antineutrinos have been a tool for fundamental neutrino research, a vector for many discoveries, and the framework for pioneering much of today's neutrino detection technology. Indeed, many of the 50s developments are at the core of today's transparent and monolithic neutrino detector exploiting Cherenkov radiation and scintillation. Despite their remarkable success leading, collectively, to several Nobel prizes, those detectors have been limited in terms of their inability to identify the particle impinging on the detector. This limitation has given shape to the overall experimental methodology for over a century, relying on cumbersome shielding, including deep underground locations, as the only possible solutions. With the invention of LiquidO (2012), detection and topological imaging are now possible, thus overcoming a challenge posed to open up a new generation of physics potential. For reactors, this implies we may distinguish to unprecedented levels the antineutrino signal (e+; antimatter) from the main backgrounds. The AntiMatter-OTech project, using LiquidO, pioneers a new generation of reactor antineutrino research where antineutrinos will be tagged via their unique antimatter signature (e+ annihilation), thus opening the potential for both industrial reactor monitoring, with direct interest to the IAEA, and fundamental research. The latter constitutes the complementary neutrino science programme of the CLOUD experiment for the characterisation of reactors using both antineutrinos and, possibly, their unobserved neutrinos. The neutrino sensitivity is so high that the main expected background is solar neutrinos to be detected, for the first time, on the surface location — a possible revolution in neutrino sciences.

White holes: formation and dynamics
2025-11-06 11:00 - 13:00 | Online
linkEinstein's theory of General Relativity allows for the possibility of the existence of remarkable and exotic macroscopic objects. Two examples are black holes and white holes. For the first, the evidence for their existence is overwhelming, and their properties have been studied in detail. White holes, on the other hand, have not received as much attention, and their existence is still an open question.Although we have not had any confirmed detections, white holes are still solutions to Einstein's equations. These are truly strange objects that defy our physics, but so do black holes up to this day. That is why further study of the formation and dynamics of these objects is necessary. A better understanding may reveal important implications for black hole physics and cosmology, which can change our understanding of the universe.In this thesis, we analyse a model for a white hole originating from an inverted Oppenheimmer-Snyder collapse. We study the possible solutions of this model, depending on the initial conditions. In addition, we study the dynamics of the white hole, with a first approach through the quasinormal modes. Finally, to compare our results with the state-of-the-art work, we review the more recent literature addressing quasinormal modes of a Schwarzschild white hole.

Cosmological signatures of the late time symmetry breaking
2025-11-06 16:00 - 18:00 | Sala P13, IST, Edifício de Matemática, 2nd floor
Our universe has already experienced a series of profound phase transitions - from the Grand Unified and electroweak epochs to the QCD transition - and it may not be finished yet. The Higgs field could reside in a metastable state, poised to decay into a true vacuum. Tiny black holes or high-energy events could catalyze this transition, creating expanding bubbles of true vacuum racing toward us at nearly the speed of light. In this talk, I will present quantitative predictions for the observable signals such a catastrophic event might generate. We estimate the Higgs particles emitted from a bubble wall, track their decay products, and derive the resulting photon and neutrino energy spectra - possible early-warning signatures that could precede the arrival of the bubble itself. I will then discuss two related scenarios: one involving a TeV-scale colored scalar that breaks SU(3)c and another involving a charged scalar that breaks U(1)EM. In both cases, the first-order phase transition produces distinctive photon and neutrino spectra that could serve as unmistakable fingerprints of an impending vacuum collapse.

Long range toric code: finite temperature topological order in two dimensions
2025-11-06 17:00 - 19:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
In traditional 2D topological order, anyons quasiparticles are deconfined: the energy required to separate two anyons arbitrarily far apart is finite.As a result, thermally excited anyons proliferate and destroy topological order at anyfinite temperature. We introduce an extension of the toric code with long-range,power law interactions that maintains topological order at nonzero temperatures. Theinteractions generate a confining potential between anyons, stabilizing the topologicalphase against thermal fluctuations. For several forms of long-range couplings, weidentify a confining topological phase below a critical temperature, where the groundstate is topologically ordered but the excitations remain confined.

Radiation sources beyond the vacuum 2-body problem
2025-11-07 10:00 - 12:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Gravitational wave astronomy revolutionized physics. My PhD focuses on the study of systems of radiation sources around massive black holes. In the first project of my PhD, we investigated the motion of a radiating charged particle around a spinning black hole in the presence of a magnetic field. These systems are important from the point of view of energy extraction mechanisms from black holes, a proposed source of high-energy cosmic rays. Our work corrected misconceptions in the literature about the dynamics of such systems and showed that one can use superradiance to extract energy from the black hole, outspiralling and drifting away from the black hole.The second, and current, project is focused on the understanding of the gravitational-wave signal produced when a stellar-mass binary orbits a spinning massive black hole. We use Dixon’s formalism to describe the stellar binary as a pointlike particle with a time-varying quadrupole moment. Using the Teukolsky formalism, we calculate the resulting gravitational radiation, produced by both the internal motion of the stellar binary components around the center of mass, and by the motion of the latter around the massive black hole. The waveform obtained, from first principles, shows rich physics, namely signatures of Doppler modulation, relativistic beaming, strong lensing, quasi-normal mode excitation, and helicity-dependent scattering. The science potential of these systems can’t be overstated, and it might be unlocked with future, more sensitive detectors like LISA. However, this requires challenging work to be done on the waveform modeling side; my PhD aims to be a stepping stone in this direction.

Incoherent Diffraction Imaging with hard X-rays: Single-shot characterization of 2D spatial coherence of a focused X-ray beam
2025-11-07 11:00 - 13:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
Achieving a compact and accessible way of performing nanoscale imaging would represent a ground-breaking step in this field. This vision is the main goal of the NanoXCAN project, which aims to develop an X-ray microscope capable of operating outside the strict coherence and infrastructure requirements of conventional X-ray imaging. A promising approach to achieve this is Incoherent Diffraction Imaging (IDI), a recently proposed technique that exploits the partial coherence of typically considered incoherent sources. To assess its feasibility in the hard X-ray regime, we conducted an experimental campaign at the Nanoscopium beamline, SOLEIL. Using custom diffusers, speckle patterns were successfully generated and characterized. Speckles suitable for IDI were produced sufficiently out of focus, where the plane-wave approximation is valid, and for small source sizes. Under these conditions, fully developed speckle patterns were obtained, validating the diffuser design for this setup. Moreover, we performed a single-shot characterization of the 2D spatial coherence using these custom diffusers’ far-field speckle pattern. This coherence analysis provided single-shot qualitative and quantitative measurements of the transverse coherence length and global degree of coherence, confirming the expected inverse dependence of coherence on source size. Under optimal conditions, the measured coherence length reached ∼ 1 μm. These results establish the experimental groundwork for future IDI demonstrations with hard X-rays and advance the NanoXCAN goal of enabling high-resolution lensless imaging beyond large-scale facilities.

Bondi-type accretion onto a Kerr black hole in the kinetic regime
2025-11-13 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
We derive an exact solution representing a Bondi-type stationary accretion of a kinetic (Vlasov) gas onto the Kerr black hole. The solution is exact in the sense that relevant physical quantities, such as the particle current density or the accretion rates, are expressed as explicit integrals, which can be evaluated numerically. We provide an analytic approximation which allows us to obtain simple formulas for the mass, energy, and angular momentum accretion rates. These formulas are used to derive characteristic time scales of the black hole mass growth and the associated spin-down in two different scenarios: assuming that the ambient energy density is either constant or decreases on a cosmological scale.

Dark Matter and Machine Learning in Multi-Higgs Doublet Models
2025-11-13 15:00 - 17:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
This thesis investigates extensions of the scalar sector of the Standard Model (SM), in particular models with N Higgs Doublets (NHDMs), applied to Dark Matter (DM) and new sources of CP violation. It combines the study of Multi-Higgs models with modern Machine Learning (ML) techniques for the exploration of high-dimensional parameter spaces. This approach is broadly applicable to any BSM scenario and offers a versatile path to uncover new physics with concrete experimental implications.First, we study the Z2xZ2 Three Higgs Doublet Model (3HDM) with two stable inert scalars, leading to a multi-component DM framework. A rigorous analysis allows us to derive new conditions for the global minimum of the potential and identify regions where both DM candidates contribute comparably to the observed relic abundance. We impose all theoretical and experimental constraints and explore their interplay and complementarity across the full parameter space. This model displays a rich phenomenology inaccessible to minimal approaches, such as the Inert Doublet Model (IDM), thereby highlighting the predictive power of scalar sector extensions.Next, we analyse the CP-violating Z2xZ2 C3HDM, which features large pseudoscalar Yukawa couplings that are tightly constrained and challenging to probe using conventional methods. To overcome this, we implement an ML-based scanning algorithm combining an Evolutionary Strategy with a Novelty Reward mechanism. This procedure accelerates the identification of new viable regions and uncovers clear predictions, particularly in the Higgs couplings to the top and bottom quarks.

Development of a LWFA target for fine electron injection control
2025-11-14 09:00 - 11:00 | Sala P9 (Piso 2 do Pavilhão de Matemática) do IST/Online
LinkLaser-plasma accelerators (LPAs) employ intense laser pulses focused into a gas target to drive plasma waves with electric fields strong enough to accelerate electrons to relativistic energies, offering accelerator facilities orders of magnitude more compact than conventional ones. Recent advances have demonstrated high-quality electron beams with up to 8 GeV energy gain [1], per- mille-level energy spread [2], 10–100 pC charge, few-femtosecond duration [3], sub-milliradian divergence, and repetition rates on the kilohertz range [4]. However, reproducibility remains a major limitation due to shot-to-shot fluctuations arising from laser instabilities, plasma density variations, and stochastic injection dynamics, hindering precision applications such as medical therapy [5] and LPA-driven X-FELs [6]. We present a novel two-chamber gas cell enabling precise, tunable control of the plasma density profile via independent temperature regulation, supporting reproducible, charge-tunable electron beam generation through a down-ramp injection scheme. The adjustable cell length facilitates energy tuning and compatibility with diverse experimental setups. Computational Fluid Dynamics (CFD) simulations using OpenFOAM [7] confirm the feasibility of the designed density profiles, while Bayesian optimization applied to particle-in-cell simulations using OSIRIS [8] identifies optimal laser–plasma parameters. Experimental assembly and testing of the gas target, including the temperature and gas injection control system, are also reported.

Multi-Higgs Doublet Models and softly-broken symmetries
2025-11-17 09:00 - 11:00 | Online
This dissertation presents an analysis of the scalar sector of two different Three Higgs Doublet Models that are invariant under the discrete symmetries Σ(36) and Δ(54). The study focuses on different Vacuum Expectation Value alignments and the mass spectra associated with each model. For every case, the effect of introducing Soft Breaking Parameters is examined, along with their implications on the physical properties of the models. The work also investigates the decay channels of the Higgs bosons and identifies a dark matter candidate. Finally, the phenomenological consequences of these models are discussed, including the possibility of Domain Wall formation, which motivates further investigation in future work.

Wearable sensors to evaluate stress and enhanced assisted rescue response
2025-11-17 14:00 - 16:00 | Sala P9 (Piso 2 do Pavilhão de Matemática) do IST
Firefighting is a physically and psychologically demanding profession that exposes individuals to extreme operational stress. To support decision-making in real time, the Safefire project developed and validated a chest-worn wearable electrocardiogram (ECG) system designed to continuously monitor physiological responses and assess stress in firefighters under realistic conditions. In this context, this dissertation evaluates the device performance across non-operational, simulated, and real operational scenarios, with a focus on robust signal acquisition, algorithmic processing, and accurate stress assessment. Using vests with MOVESENSE sensors and two electrodes placed bilaterally on the lower chest, ECG signals were acquired from 46 firefighters and IST students, during physical exertion and stress-inducing activities. To mitigate noise and motion artifacts, the data-processing pipeline integrated automated R-peak detection with real-time signal-quality validation. User evaluations indicated overall satisfactory comfort and usability, with minor issues related to body awareness and device stability. Two textile materials (MDPF and MPPAF) were tested for the electrode areas. Both displayed significant reductions in signal quality under repeated wash and operational use. Physiological analysis confirmed that heart rate variability (HRV) indices reliably reflected changes in activity intensity, and enabled differentiation between physical effort and psychological stress through a corrected RMSSD parameter. Overall, the findings confirm the feasibility of integrating real-time signal-quality monitoring and stress assessment in wearable ECG systems for high-risk environments, while highlighting ongoing challenges related to comfort, durability, and consistent signal acquisition.

Advanced Digital Encoder Design for Next-Generation Smart RFID Tags in Textile Industry Digital Product Passports
2025-11-17 16:00 - 18:00 | Sala P9 (Piso 2 do Pavilhão de Matemática) do IST
This dissertation presents the development of a printed UHF RFID antenna for textile integration, targeting digital traceability within the European Union's forthcoming Digital Product Passport (DPP) framework. The work addresses the challenge of embedding passive RFID technology early in the textile value chain, ensuring electrical stability, mechanical flexibility and resistance to the harsh textile processing conditions.A water-based conductive ink composed of silver nanoparticles, PEDOT:PSS and a polymer adhesive was formulated and optimized for screen-printing and heat-transfer application. Among several formulations, the 2:2:1 ratio (silver:adhesive:PEDOT:PSS) achieved the best balance between conductivity, adhesion and printability, reaching sheet resistances in the 101-102 Ω range. Comparative evaluation of transfer media identified MTBGR25 as the most suitable transfer paper, enabling complete and uniform transfer of printed structures onto textile substrates.Optimal heat-pressing parameters were established at 150-180°C for 30s for different textile substrates, ensuring reliable adhesion and conductivity without thermal degradation. Mechanical durability tests confirmed the robustness of the printed ink, with only a 3% change in resistance after 1000 bending cycles and almost full recovery after rest periods, indicating excellent flexibility and interfacial stability. Water Vapor Transmission Rate (WVTR) analysis confirmed that the printed layers preserved 60–70% of the original breathability of the fabrics, ensuring compatibility with textile applications.Overall, the study demonstrates the feasibility of producing durable, flexible and environmentally compatible printed RFID antennas suitable for textile integration. The developed materials and process optimizations provide a foundation for scalable manufacturing of smart textiles aligned with circular economy and digital transparency initiatives.

From Dark Sectors to the Axion-Neutrino Connection
2025-11-18 10:00 - 12:00 | Sala V1.01 (1º Piso do Pavilhão de Civil) do IST
The Standard Model (SM) of particle physics provides a successful description of fundamental particles and their interactions but fails to explain phenomena such as neutrino oscillations, dark matter (DM), and the baryon asymmetry of the Universe. These clear signs of physics beyond the SM (BSM) motivate extensions introducing new particles and symmetries. Theoretical questions like the flavor puzzle – fermion masses and mixing – and the strong charge-conjugation and parity (CP) problem further guide BSM frameworks. This thesis explores BSM scenarios based on two guiding principles: constructing unified frameworks that address multiple open problems in (astro)particle physics and cosmology, and emphasizing their experimental testability through detailed phenomenological analyses. This approach uncovers deep connections between seemingly disconnected sectors, offering a more complete view of fundamental physics. We investigate dark sector models for the origin of neutrino masses, proposing a novel setup: the dark linear seesaw, which radiatively links neutrino mass generation to viable DM candidates and predicts charged lepton flavor violation. In these scenarios, dark sector particles can constitute weakly interacting massive particle (WIMP) DM, testable via direct detection experiments. We study spontaneous CP violation induced by a complex scalar singlet, acting as a common origin of low- and high-energy CP violating effects relevant for leptogenesis.We also analyze a Nelson-Barr model that solves the strong CP problem, generates a realistic CKM matrix radiatively, and yields scalar WIMP DM. Additionally, we present unified axion frameworks in which a colored sector radiatively generates neutrino masses. These models predict distinctive axion couplings to photons and fermions and accommodate axion DM in both pre- and post-inflationary cosmologies. Finally, we explore minimal flavored Peccei-Quinn symmetries that link the flavor puzzle, neutrino masses and DM within a predictive and testable BSM framework.

Design and modeling of a plasma reactor for the production of O2 from the conversion of CO2
2025-11-18 14:00 - 16:00 | Online
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Studies on the RICH Velocity Reconstruction with a Likelihood Approach. Features and Variability Corrections
2025-11-18 14:00 - 16:00 | Online
The Alpha Magnetic Spectrometer (AMS) is a particle physics detector operating on the International Space Station, designed for long-term precision measurements in space. A key objective of AMS is the isotopic separation of cosmic rays, providing crucial insight into their origin, propagation, and composition. Achieving accurate isotopic separation depends critically on the mass resolution, which is strongly determined by the velocity resolution at high energies.The Ring Imaging Cherenkov Detector (RICH) is the AMS subdetector responsible for high-precision velocity measurements in the upper energy range. Improving its velocity resolution is therefore essential to extending AMS sensitivity to isotopic identification in previously unexplored energy domains.The RICH determines particle velocities by reconstructing Cherenkov ring patterns produced as particles traverse one of its radiator materials, aerogel or sodium fluoride.This work reports possible improvements to the velocity reconstruction performed by the LIP likelihood-based algorithm.One enhancement involves exploiting Cherenkov photons emitted from the plastic foil support below the radiator. Jointly reconstructing the rings from both the foil and the radiator is expected to improve velocity resolution for high-charge particles.A second improvement addresses time-dependent biases in reconstructed velocities. Periodicities of 60 days and one year, linked to the temperature dependence of radiator refractive indices, and a long-term drift from light guide and aerogel ageing are identified. Modeling these effects enables time- and temperature-dependent corrections to the refractive index and emission point used in reconstruction.

Solving the Teukolsky Equation with spectral methods
2025-11-18 14:00 - 16:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
General Relativity is to this date the best theory of gravity we have and probing the very nature of Black Holes is possible through events such as Gravitational Waves. In this work we describe our time domain solver of the 1+1D homogeneous Teukolsky equation, an equation that encodes the physics of linear perturbations in Kerr spacetime. We solve it in hyperboloidal slices to be able to extract the signals at $\mathcal{I^+}$ without the need for extrapolation.To do so we developed a code that employs two different kinds of spectral methods: a known pseudo-spectral scheme with collocation and a novel fully spectral scheme without collocation. With this second approach we obtain more accurate late-time power-law tails, as well as their decay rates, and we have achieved results for negative spin-weights without the use of quad precision that many suggest is necessary. Our results are in agreement with analytical and empirical generalizations of Price’s Law for Kerr Black Holes. Then we proceed with a study of the convergence properties of both spectral schemes and of the time-symmetric integrator we use. This integrator is implicit and it shows advantages relative to the more usual explicit integrators mainly in terms of efficiency, but possibly also in terms of accuracy whenever we introduce source terms into the equation. Thus, this work marks a first step to solve the full Teukolsky system and thus evolve Extreme-Mass Ratio Inspirals simulations accurately and efficiently.

_Solving the Teukolsky Equation with spectral methods
2025-11-18 14:00 - 16:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
General Relativity is to this date the best theory of gravity we have and probing the very nature of Black Holes is possible through events such as Gravitational Waves. In this work we describe our time domain solver of the 1+1D homogeneous Teukolsky equation, an equation that encodes the physics of linear perturbations in Kerr spacetime. We solve it in hyperboloidal slices to be able to extract the signals at $\mathcal{I^+}$ without the need for extrapolation. To do so we developed a code that employs two different kinds of spectral methods: a known pseudo-spectral scheme with collocation and a novel fully spectral scheme without collocation. With this second approach we obtain more accurate late-time power-law tails, as well as their decay rates, and we have achieved results for negative spin-weights without the use of quad precision that many suggest is necessary. Our results are in agreement with analytical and empirical generalizations of Price’s Law for Kerr Black Holes. Then we proceed with a study of the convergence properties of both spectral schemes and of the time-symmetric integrator we use. This integrator is implicit and it shows advantages relative to the more usual explicit integrators mainly in terms of efficiency, but possibly also in terms of accuracy whenever we introduce source terms into the equation. Thus, this work marks a first step to solve the full Teukolsky system and thus evolve Extreme-Mass Ratio Inspirals simulations accurately and efficiently.

Developing tools for the recovery of historical audio recordings
2025-11-18 14:00 - 16:00 | Online
LinkMagnetic tape recordings hold historically irreplaceable audio, yet many recordings are unplayable due to physical and chemical degradation, which pose challenges to their preservation. This thesis develops tools for recovering audio from data obtained using non-contact readout techniques, such as X-ray Magnetic Circular Dichroism (XMCD) and Tunneling Magnetoresistance (TMR) sensors. Signal denoising was tackled using three methods: Extended and Unscented Kalman Filters for model-based denoising, with the UKF producing cleaner spectrograms than the EKF, but both requiring extensive tuning; Spectrogram soft-masking with Griffin-Lim phase reconstruction, which effectively removed broadband noise for isolated tones but introduced artifacts for complex sweeps; and a two-stage U-Net (Moliner et al.) pretrained on gramophone recordings, which revealed obscured harmonic content in a Beethoven excerpt, illustrating the promise of deep learning for this task, but still needs further validation and fine-tuning. A recording-to-readout simulation pipeline was implemented. It incorporates the Karlqvist field, AC bias, hysteresis behavior via Jiles-Atherton and Preisach models, includes Mallinson-type noise, and represents the XMCD beam as a skewed Gaussian convolution. Experimental hysteresis loops were fitted using both models, with the Preisach providing superior accuracy (NRMSE 3.83%) compared to JilesAtherton. This framework enables the study of particle statistics and measurement parameters on the recovered signal. These tools form the basis for future reconstruction of real historical audio from degraded tapes using XMCD measurements. The simulation tools were validated on experimental XMCD scans of 1 kHz, 1-20 kHz and musical excerpts, confirming the feasibility of non-contact audio recovery

Characterization of Color centers in diamond for quantum sensing
2025-11-19 15:00 - 17:00 | Sala V1.24 (Piso 1 do Pavilhão de Civil) do IST/Online
Nitrogen-Vacancy (NV) centers in diamond are versatile quantum systems that combine single-photon emission with spin-dependent fluorescence. These properties have established NVs as a leading platform in the fields of quantum communication, computation, and sensing. Their spin-dependent optical readout enables nanoscale magnetic field detection. Moreover, the exceptional chemical stability and biocompatibility of diamond make NVs suitable for applications ranging from condensed matter to biology.In this work, NV centers created in bulk diamond and nanodiamonds using different creation methods were characterized to investigate how fabrication conditions affect their optical and spin properties. Confocal and hyperspectral microscopy, emission spectroscopy, fluorescence lifetime imaging microscopy and optically detected magnetic resonance experiments were employed to probe the NV centers.A comparative analysis was conducted between NVs created by ion implantation, high-temperature electron irradiation, and femtosecond laser writing. The ion-implanted bulk diamond presented well-defined quantum signatures with a dephasing time T2* = 118 ± 19 ns. Nanodiamonds with NV centers exhibited stable fluorescence, although with broader resonances indicating reduced magnetic sensitivity. In contrast, NV ensembles generated by femtosecond laser writing demonstrated tunable photoluminescence, strongly dependent on laser writing parameters such as pulse energy, exposure time, and writing depth. The NV spots, located about 50 μm deep, show a long dephasing time, T2* = 0.32 ± 0.12 μs. These findings offer valuable insight into the optimization of NV-based quantum sensors by emphasizing that the fabrication method, which determines the NV centers’ depth and local environment, directly impacts their spin and optical properties.

Examining the Hubble tension with differences in supernova and host galaxies properties
2025-11-19 16:00 - 18:00 | Sala V1.01 (Piso 1 do Pavilhão de Civil) do IST/Online
LINKThe persistent 4–6σ discrepancy between early- and late-time measurements of the Hubble constant ( ) is known as the "Hubble tension" and represents one of the major open problems in modern cosmology. In this work, we investigate how differences in light-curve parameters ( , ) and host galaxy properties ( e sSFR) between the calibration and Hubble Flow (HF) Type Ia supernova (SN Ia) samples affect the SN luminosity standardization and the estimation. To do that, we generate subsamples from both samples and use them to estimate , , α, β, and . Both one- and multi-dimensional Kolmogorov–Smirnov tests are used to evaluate the consistency between the subsamples property distributions and analyze how the estimated parameters vary with the better matching of the subsamples. We find that the calibration sample is not fully representative of the HF sample, particularly in and sSFR. Improving consistency between subsamples leads to significant trends in , , α and , although overall values remain broadly stable. More consistent subsamples also tend to produce a mass step consistent with zero within 1σ. We also try to disentangle SN subpopulations using different approaches, identifying consistent differences in ( 2–3σ) and ( 2σ), estimated using low- and high-stretch SN subpopulations, likely due to variations in dust properties and intrinsic color that are not captured by the standard β parameter. This results also suggest that the underlying SN subpopulations might contribute to additional dispersion in estimates.

Analog logic gate of structured light based on nonlinear optical neural networks
2025-11-20 12:00 - 14:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
Optical Neural Networks combine the typical architecture of a neural network, with the advantages of using light to store the information and perform the operations. They have multiple applications like image recognition or optical computing. Nonlinearity can be added to these systems by having layers of materials with a nonlinear response in their interaction with light. This project aims to use a nonlinear optical neural network as basis for an all optical decoder, showing the potential of these systems. Moreover, this work focuses on designing and experimental implementing the physical neural network. It starts with a study on the Kerr nonlinearity of selected materials in order to choose the best. Such study required performing z-scans and I-scans on the samples. Through these measures, the best sample to use in the experiment was found to be a gold bearing glass. Then, the focus was to improve a machine learning model to act as a digital twin to the real system. This model served to test system architectures and will be responsible for training the parameters later fed into the physical neural network. Following this, a real experimental setup was designed, assembled and aligned. The latter presented several challenges that had to be overcome. As a first approach, a linear model was chosen for testing. The model was trained in silico and then tested in the real setup, and such results are presented. The work here presented provides a ground base for the experimental implementation of an all optical decoder.

Static and reconfigurable polarization shaping towards high-power
2025-11-20 14:00 - 16:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
Vector beams are optical fields with anisotropic polarization profiles that enable tight focusing, multiplexing, and sensing applications, among others. Yet, most generation mechanisms are either alignment-sensitive and lossy, when using interferometry and/ or SLMs, or static when fabricated, when relying on metasurfaces, limiting reconfigurability and high-power use. In this work, we first benchmark these limitations experimentally: an interferometric SLM setup produced a radially polarized beam but revealed residual ellipticity and strong sensitivity to alignment through Stokes polarimetry, establishing a baseline for improvement. Next, we designed and fabricated an all-silica metasurface to emit radial or azimuthal vector beams. This material is very appealing for high-power applications due to its high damage threshold. However, analyzing the device revealed pattern merging, and experimental observation showed deviations from the ideal donut, highlighting the challenges of phase accumulation intrinsic to low-index silica. Building on these research steps, we propose a reconfigurable vector-beam generator that pairs a single, disorder-engineered birefringent layer with control of the input's complex amplitude, learned by a polarization-aware, differentiable Fourier-optics simulator. The machine learning algorithm optimizes the input complex amplitude to synthesize arbitrary vectorial targets using the same random medium, maximizing the overlap between them and the output. By disorder-engineering with grid-search techniques and by backpropagation methods, we obtained overlaps of 0.98, 0.97, and 0.92 for a radial, lemon, and star target, respectively. We were then able to create an algorithm that performs multi-target optimization using a single birefringent layer. This method has the fundamental advantage of being scalable to high-power.

Numerically solved, but not yet understood: recent advancements in the gravitational twobody problem
2025-11-20 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The study of black holes' resonant excitation and their subsequent relaxation ("Black Hole Spectroscopy") is a fundamental tool to observationally investigate gravity in its most dynamical and violent regime. Recently, the unprecedented loudness of the gravitational wave signal GW250114 allowed us to exploit spectroscopic techniques to achieve the first accurate verification of two long-standing predictions of general relativity: Hawking's Area Law and the Kerr nature of the source. The physical process behind these signals, namely the end state of the gravitational two-body problem, has been numerically solved twenty years ago. However, despite the striking simplicity of black holes, and decades of developments in classical perturbation theory, a first-principles understanding of the dynamical stage in which two black holes fuse together (the "merger" regime), is still lacking. Such ignorance prevents even more exciting observational explorations, and the construction of signal models in richer scenarios. In this seminar I will detail recent breakthroughs in this direction, and their potential to advance our understanding of gravity, searches for new physics, and to harvest the full potential of next-generation detectors in achieving high-precision measurements.

Biocompatible flexible photosensors based on 2D materials and crystalline organic semiconductors
2025-11-21 14:00 - 16:00 | Anfiteatro PA2 (Piso -1 do Pavilhão de Matemática) do IST
Photoactive organic semiconductors combine effective light absorption and photogeneration with lightweight, flexibility and biocompatibility, making them highly attractive for biological photodetection applications, such as visual prosthesis. [1,2] Organic single crystals (SCs) stand out due to an efficient and stable light sensitivity, granted by their long-range periodic molecular order and chemical purity, that reduce energetic disorder, enhance charge carrier mobility, and promote well-defined optical transitions. Solution-based processes, as spin-coating or spray deposition, have also been explored for the fabrication of photoactive media. [3,4]This work investigates organic photodetectors based on small molecule semiconductors targeting different regions of the visible spectrum: rubrene for blue-green (~450–550 nm), PTCDA and PTCDI-C8 for yellow-red (~550–600 nm), and TCNQ and 9-Fluorenone for violet-blue (~400–450 nm).Rubrene SCs devices, grown by Physical Vapor Transport (PVT), exhibited efficient photocurrent generation, with responsivity between 10⁻⁵ to 10⁻³ A/W near 460 nm. PTCDA could not be crystallized by PVT due to its high thermal stability, while PTCDI-C8 crystalline films yielded ohmic conductivity but failed to generate measurable photocurrent. TCNQ SCs showed responsivity and EQE values, respectively, in the range of 0.1–1 mA/W and 10⁻⁷ %. Spin-coated TCNQ and 9-Fluorenone films displayed partial crystallization, but low absorbance which hindered photosensitivity, likely due to insufficient thickness and solvent-induced charge traps.Overall, the results confirm the potential of organic semiconductors, particularly single crystals, for biocompatible photodetectors. However, further optimization, especially of film deposition and device architecture, is necessary to enhance light absorption, carrier transport and reproducibility.

Towards the neutrinoless double-beta decay study with SNO+: radioactive background characterisation with SNO+ scintillator data
2025-11-24 10:00 - 12:00 | Online
0νββ is one of the most relevant processes in particle physics, as it has the potential to unveil the Majorana neutrino’s nature, and its mass generation mechanism. SNO+, a multipurpose neutrino detector, will load 130Te into its large liquid scintillator in order to search for this rare process. The aim of this thesis is to characterize all the SNO+ backgrounds that are potentially dangerous for the 0νββ signal in data collected before SNO+ loads Tellurium. This work included three main steps: (T1) identification of the dataset to use; (T2) selection of variables to remove known backgrounds and (T3) fit of the resulting energy spectrum. (T1) was performed using a coincidence tagging technique, which allows analysing an excess in 214Bi following from Rn ingress. In (T2) backgrounds like instrumentals, muons, externals, coincident and pile-up events have been rejected. The impact of these cuts was evaluated on livetime and efficiency. In (T3) Maximum likelihood fits were performed on data, collected between May 2022 and March 2023 (228.2 net livetime days). Background PDFs from the 238U, 232Th and 235U chains, muon induced backgrounds and Solar neutrinos were used. Lastly, the time dependence of events above 1.5 MeV, was studied in intervals of 15 days, for the three energy regions: [1.5,1.8], [1.8,2.2] and [2.2,2.6] MeV to see any potential deviation from a constant trend, indicating a background ingress.

QUANTUM FINANCE: Path Integrals and Hamiltonians for Option Pricing
2025-11-24 10:00 - 12:00 | Sala V1.34 Edifício de Civil
The thesis starts by explaining a practical problem: classic option models assume constant volatility and can’t explain the "smile" seen in real markets. The goal is to use tools from physics to price options when volatility moves over time, and to check that the method works on real data . First, the text reviews the basics of option pricing: no-arbitrage ideas, how Black–Scholes is derived, and why real markets need a model where volatility itself is random (the Merton–Garman equation). Next, the thesis rewrites these pricing equations in a physics style. Instead of only solving a differential equation, it thinks of prices as coming from a "kernel" or "propagator" that tells how today’s price depends on all possible future paths. This view helps us see clearly how parameters like correlation, mean reversion, and volatility-of-volatility shape option prices. Then come the numerical methods. Two approaches are built and compared. One simulates the joint movement of price and volatility step by step (Euler/Milstein). The other uses a path-integral trick to integrate out the price path and only simulate the volatility path, which saves memory while staying accurate. Prices are turned into implied volatilities so results can be compared fairly. With market data (SPY options), the thesis sets up a calibration: pick model parameters so the model’s implied volatilities match the market’s. To speed this up, a neural network is trained to act as a fast "surrogate" for the heavy calculations. It predicts well and makes calibration much faster. Finally, the same framework is extended to path-dependent products. By adding simple "potentials," it prices barrier and Asian options and checks the results against Monte Carlo. The work ends with a summary of accuracy, speed, and what each parameter does, plus ideas for future improvements.

Particle Drifts and Radiation Reaction in Astrophysics
2025-11-24 14:00 - 16:00 | V0.07, Floor 0, Civil Engineering Building
In the presence of strong electromagnetic fields, the energy radiated by accelerated relativistic charged particles becomes comparable to their kinetic energy. Under such conditions, radiation reaction, i.e., the recoil charges experience when radiating, must be taken into account to correctly describe particle motion. Earlier results have shown that, in the radiative regime, initially stable relativistic plasmas subject to a strong uniform magnetic field will develop ring-shaped momentum distributions with inverted populations. These distributions are unstable to maser-type kinetic instabilities capable of coherent radiation, whose properties align to those observed in pulsars and Fast Radio Bursts. In this thesis, we generalize the previous result to account for other non-uniform configurations of the electromagnetic fields. First, we investigate single particle dynamics and derive the equations of motion for the guiding center of a particle in the radiative regime. Second, we study the effects of a drift velocity, with an emphasis on the curvature drift, on the momentum distribution of a radiatively cooled plasma. Our findings show that plasmas will develop spiral momentum distributions if the drift velocity is high enough. Criteria for the different regimes are determined. Lastly, we study beam-plasmas undergoing radiative cooling as they travel along the field lines of a static magnetic dipole. Our results are corroborated via test particle simulations employing a fully-parallelized pusher using the Landau-Lifshitz model for classical radiation reaction, developed for this thesis. We conjecture the physics explored here is relevant in providing intuition for the dynamics of astrophysical plasmas and for coherent radiation generation.

Pile-up event identification and rejection in SNO+: enhancing the signal to noise ratio
2025-11-24 15:00 - 17:00 | Online
This thesis has been developed in the context of the SNO+ experiment, a multipurpose neutrino detector whose goals include the search of the neutrinoless double beta decay, low energy solar neutrinos, supernova neutrinos and geological and reactor anti-neutrinos. To achieve these goals SNO+ requires a precise modelling of its backgrounds. Several techniques are employed to guaranty the purity of the samples and materials, as well as various methods for the identification and rejection of single event backgrounds. Nevertheless, this is not a complete picture of all the backgrounds present in the experiment. The main goal is the study of one of these classes of backgrounds particularly difficult to identify: the pile-up events. These are events that happen in the same trigger window (460 ns) and are therefore reconstructed as a single event. As a consequence, low energy events can be shifted into the region of interest and/or reconstructed in inner volumes, impacting many analyses. However, due to their nature, pile-up event's characteristics can differ from single events making the identification techniques, developed for those type of events, ineffective. Therefore, new identification and rejection techniques for pile-up events are required. The strategy developed and presented in this thesis will consist of three main steps (1) study of the type and amount of pile-up events, (2) identification of the variables that characterize these events, (3) comparison between Monte-Carlo simulation and data for two main phases of SNO+.

Reduced Models for Plasmas: Integration of "particle-in-cell" Simulations and Machine Learning
2025-11-24 16:00 - 18:00 | Sala V0.07 - Pavilhão de Civil
Accurate reduced models are essential to describe plasma dynamics across scales while maintaining computational feasibility for large-scale simulations. These models require closure relations that connect macroscopic fluid quantities to the underlying kinetic behaviour, and recent data-driven approaches have shown potential for deriving such relations directly from kinetic simulations. In this work, a sparse-regression framework based on the Sparse Identification of Nonlinear Dynamics (SINDy) algorithm is adapted to infer fluid equations from fully kinetic OSIRIS Particlein-Cell simulations. The method is first benchmarked using the two-stream instability, extending previous work by accurately reconstructing the hierarchy of fluid moments up to the third-order equation. Using both the two-stream instability and a linear electron–plasma–wave configuration, we assess under which conditions sparse regression recovers the hierarchy of fluid equations with a waterbag closure and identify its limits as non-linear phase mixing develops. We show that sparse regression can extract compact and physically interpretable reduced plasma models directly from kinetic simulations, providing a data-driven path toward machine-learned closures applicable to future relativistic and hybrid plasma studies.

General-relativistic radiation reaction cooling in pulsar magnetospheres
2025-11-25 09:00 - 11:00 | Anfiteatro PA2 (Piso -1 do Pavilhão de Matemática) Alameda
The origin of coherent radio emission in pulsars is a long-standing open problem in astrophysics. A promising candidate is radiation reaction cooling, which has recently been shown to trigger the development of anisotropic ring-shaped distributions in momentum space. Radiation reaction continuously sustains population inversion across timescales comparable to the dynamical evolution of the system in the relativistic pair plasmas present in the magnetospheres of pulsars, thereby powering the emission of linearly polarized coherent radiation via the electron cyclotron maser (ECM) instability.In this Thesis, we further investigate this mechanism by studying how the phase-space dynamics of radiatively cooled plasmas are modified by curved spacetime effects. For this purpose, we derived the radiative Einstein–Vlasov–Maxwell system, along with the curved spacetime extension of the Landau-Lifshitz model of radiation reaction, in the 3+1 formalism of general relativity. In addition, we developed a general-relativistic particle pusher to integrate particle trajectories in stationary electromagnetic fields and background spacetime metrics, by extending an existing parallelized code.Our simulations show that ring distributions are generated in Schwarzschild and slowly rotating Kerr spacetimes, with enhanced properties. Increasing the stellar compactness amplifies the momentum-space gradient that regulates the growth rate of the ECM instability, while frame-dragging induces a stellar electric field and acts as an external source of perpendicular momentum, extending the duration of the ring structure. This work constitutes the first systematic investigation of radiation reaction cooling in curved spacetime, and establishes the foundation for future investigations of this mechanism in realistic astrophysical conditions.

Plasma Instabilities in the Fireball experiments at CERN and INFN
2025-11-25 14:00 - 16:00 | Sala de Formação Avançada - Piso 2 Pavilhão de Física

Plasmonic Nanoparticles in Oxide Thin Films for Sensing Applications
2025-11-25 16:00 - 18:00 | Anfiteatro VA1 - Pavilhão de Civil do IST
Oxide semiconductors such as Ga2O3, ZnO, and CuO are promising materials for various applications due to their stability and tunable electronic properties. Incorporating plasmonic nanoparticles into these materials enhances their optical and electrical performance through localized surface plasmon resonance (LSPR). In this work, Ag and Au nanoparticles were embedded into Ga2O3, ZnO, and CuO thin films to study their plasmonic behaviour and evaluate their potential in temperature sensing and photodetection.The formation of metallic nanoparticles in Ga2O3 thin films by ion implantation was demonstrated for the first time, as confirmed by optical and structural characterization. Plasmonic absorption bands appeared at 400–600 nm for Ag and 500–700 nm for Au, exhibiting red-shifts with increasing annealing temperature. Heavy ion irradiation revealed nanoparticle redistribution toward the surface and shape elongation.A comparative study of ZnO and CuO thin films with Au nanoparticles formed by ion implantation and in situ growth was performed to investigate the temperature dependence of the LSPR. Optical transmittance measurements showed a reversible red-shift of the LSPR peak with increasing temperature, consistent with theoretical predictions.Finally, photodetection tests revealed that, under visible light, implanted Ga2O3 films displayed noticeable sub-bandgap photocurrents attributed to defect states rather than plasmonic effects. Au-ZnO demonstrated significantly enhanced photoresponses comparatively to its undoped film, particularly under illumination resonant with the nanoparticles, suggesting that plasmonic effects were involved. In contrast, the inclusion of the nanoparticles in Au-CuO decreased its dark current, as well as its responsivity.

Kinetic Simulations of Highly Magnetized Plasmas
2025-11-25 16:00 - 18:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST/Online
LinkEfficiently modeling highly magnetized plasmas is essential for applications ranging from astrophysics to fusion, yet first-principles simulations become prohibitively expensive when high gyrofrequencies must be resolved. We develop and test two special-relativistic particle pushers using the guiding center approximation (GCA) within the state-of-the-art OSIRIS particle-in-cell (PIC) framework.The first, the GCA pusher, updates the parallel velocity explicitly and advances the guiding center position implicitly via fixed-point iteration, extending prior work by including both the mirror force and the Grad-B drift. The second, the GCA-correction pusher, modifies the Boris pusher by retaining its parallel update while imposing guiding center drifts on the perpendicular motion; extending previous attempts that considered only the EXB drift.We benchmark both against the Boris pusher using test particles in prescribed electromagnetic fields, from simple analytical configurations isolating individual drifts to turbulent fields self-generated by a three-dimensional PIC simulation of the Weibel instability. Our results show that, unlike the Boris pusher, the GCA pusher accurately captures particle dynamics when the gyrofrequency is underresolved, provided spatial scales of the electromagnetic field variation are well resolved and the GCA remains valid. The GCA-correction pusher is currently less robust due to time-centering issues, but achieves comparable accuracy in some regimes while offering higher efficiency.These findings demonstrate that GCA-based pushers enable accurate modeling of kinetic physics in strongly magnetized plasmas with much larger time-steps than conventional PIC, opening a path to significant computational speedups, improving our ability to model both astrophysical and laboratory fusion plasmas over relevant scales.

Optimization of a Transformer-Based Model for Flavour-Tagging in the ATLAS Experiment
2025-11-25 16:00 - 18:00 | Online
The Standard Model is the most widely accepted theory in the field of particle physics. In order to test and find some of the missing pieces of the theory, several experiments are being made around the world. One of the main drivers of experimental particle physics research are collider experiments, where particles are accelerated and carefully made to collide at specific regions with detectors ready to collect the products of the interaction. This data is later treated and the events reconstructed so that it is possible to learn about the phenomena occurring near the collision point. This complex task has several stages, one of which is called jet flavour-tagging, that aims to identify the flavour of the particles that originated jets after the collision. Machine learning models are employed with this task due to its complexity derived from the large amounts of data collected from each collision. One such model, created by the ATLAS Collaboration, called GN2, is studied in this work with a focus on the input variables it receives. In this thesis, different versions of the model were created with different input variables to test their importance to the model’s performance. Additionally, a study was conducted to directly test the impact of these input variables on the model’s decision-making, and the results suggest that a group of these variables related to the number of particle interactions with the detector may have a limited effect on the model.

Data-Driven Methods for Anomalous Resistivity in Collisionless Shocks
2025-11-26 09:30 - 11:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
Collisionless shocks play a central role in plasma heating, magnetic field amplification, and nonthermal particle acceleration in both space and astrophysical plasmas. Their study, however, has long been challenged by its multi-scale nature, where microscopic-scale kinetic processes can influence the large-scale dynamics of the system and vice-versa. Accurately capturing the nonlinear interplay between micro- and macro-scale collisionless shock dynamics remains an outstanding problem. In this Thesis, we explore the development of data-driven reduced models that can more efficiently capture the impact of microphysical instabilities on the largescale shock dynamics. We perform first-principles particle-in-cell simulations of collisionless shocks and describe the corresponding electric field by a generalized Ohm’s law, separating the contributions of transversely-averaged (mean-field) quantities and fluctuations due to transverse micro-instabilities. We then use convolutional neural networks to describe the fluctuations in terms of mean fields, closing the system. We demonstrate the ability of this procedure to learn effective reduced models and reproduce the spatiotemporal profile of the anomalous electric field induced in a collisionless shock. We then explore network interrogation methods to help identify the physical terms most relevant to our network-based surrogate anomalous field. This led to the identification of the mean quantities that control the dynamics of collisionless shocks and, in the future, could also inform the search for more interpretable reduced models. Our work opens the way to the incorporation of data-driven reduced models on fluid codes that could capture the effect of unresolved kinetic processes on the largescale collisionless shock dynamics.

Nanoelectronic chip design: from physics principles to circuit design for production
2025-11-26 10:00 - 12:00 | Online
LINKThis thesis presents the complete development workflow of a nanoelectronic device — from fabrication and electrical characterization to modeling and circuit-level design integration. The work focuses on the memristor, a passive two-terminal resistive device whose resistance depends on the history of electrical stimuli, thereby exhibiting memory. Such devices may play a key role in neuromorphic systems — computing architectures inspired by the human brain that promise large gains in energy efficiency and parallel information processing compared to conventional von Neumann systems. Two fabrication processes were developed to produce memristors based on MgO and Si/Ag resistive switching mechanisms, both yielding functional devices. The MgO devices exhibited OFF/ON ratios of approximately 10⁴ and switching voltages of 1.5 V (SET) and –0.2 V (RESET), while the Si/Ag devices showed ratios up to 10⁶ with lower activation voltages of 0.3 V (SET) and –0.1 V (RESET). A dedicated setup was developed to measure the noise spectral density of memristive devices and was used to characterize commercial Knowm memristors, revealing a correlation between device resistance and noise amplitude. A voltage-controlled memristor model based on the VTEAM formulation was implemented in Verilog-A and validated through simulations in Cadence Virtuoso, enabling its integration into circuit-design workflows at INESC MN. Additionally, a low-power, low-noise neural preamplifier was designed, achieving a gain of 66 dB and an input-referred noise of 17 µV, suitable for integration in a memristor-based neuromorphic circuit.

Exploring the electromagnetic shower profile to enhance the Pierre Auger Observatory physics capabilities
2025-11-27 09:00 - 11:00 | Online
This work investigates two complementary strategies to enhance the physics capabilities of the Pierre Auger Observatory. The first examines the identification of vertical neutrino-induced air showers using the electromagnetic and muonic surface signals, Sem and Sμ. Simulations of proton and neutrino primaries using CORSIKA and the Auger Offline framework indicate that Xmax should not be directly included, as its information is largely encoded in Sem and Sμ. Additionally, it was shown that muon neutrino-induced showers can also be detected using the above Sem - Sμ methodology, offering a meaningful improvement in differential neutrino flux limits.In the second part of this thesis, it is investigated the technique of radio interferometry as a method for reconstructing the electromagnetic longitudinal profile of extensive air showers. Using ZHAireS simulations, it was shown that there is a strong link between the EM profile shape and the one reconstructed from radio simulations. Significant differences in the longitudinal shape parameters, R e L, were observed between averaged showers of different primary compositions, demonstrating the technique’s potential for primary composition studies at full duty-cycle.These results highlight the complementary impact of surface signal analysis and radio interferometry, while muon neutrinos can enhance neutrino detection limits, RIT provides an independent, high-precision method to access shower development, offering a promising avenue for improving ultra-high-energy cosmic-ray and neutrino observations.

Characterization of anomalous air shower events in SWGO
2025-11-27 11:00 - 13:00 | Online
The interaction of very-high-energy Gamma Rays and Cosmic Rays with the Earth’s atmosphere leads to the production of cascading particle events known as Extensive Air Showers (EAS). Through the use of state-of-the-art simulations, we have the opportunity to study these events and how they are detected by ground-based Water Cherenkov Detector (WCD) Arrays, an essential step in the development of the forthcoming Southern Wide-field Gamma-ray Observatory (SWGO). These simulations enable the testing and definition of new variables to characterize shower features at ground level and to relate them to the shower’s longitudinal development.This work focuses on identifying and developing variables that can be used to reduce gamma/hadron background, to identify anomalous and rare events, and to distinguish between different hadronic interaction models. Through this study, we will acquire valuable insights into the underlying physical mechanisms behind shower development and to improve current methods for gamma/hadron discrimination. These aspects are crucial for the correct operation of observatories such as the future SWGO, which will rely solely on its large and dense detector array to distinguish between the electromagnetic and muonic components of air showers.

The Plasma Way to Ammonia: Modelling and Understanding Plasma-Derived NH₃
2025-11-27 11:00 - 13:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building/online
LinkThis thesis addresses the fundamental challenges of modeling 𝑁2 − 𝐻2 plasma chemistry for ammonia synthesis using plasmas, a sustainable alternative to the Haber-Bosch process. Conducted within the PSI.COM project in collaboration between Instituto Superior Técnico (Lisbon) and LPP-École Polytechnique (Paris), the work bridges experimental characterization and computational modeling of coupled electron kinetics, heavy-species chemistry, and surface reactions. An experimental campaign at LPP characterized 𝑁2 − 𝐻2 plasmas using optical emission spectroscopy, Fourier-transform infrared spectroscopy, and temperature diagnostics, revealing peak ammonia production around 70% 𝐻2 with counter-intuitive pressure dependencies. A comprehensive kinetic database was developed through systematic literature review, identifying order-of-magnitude discrepancies in rate coefficients. The chemical model integrates volume reactions and a mesoscopic surface model that describe the main plasma features in terms of discharge characteristic and concentrations of relevant species. Significant computational advancements were achieved through implementation of a variable energy grid in the LisbOn KInetics Boltzmann (LoKI-B) solver, reducing computational costs while maintaining accuracy. A graphical user interface for input was developed to democratize the use of LoKI-B within the scientific community, facilitating input parameter specification and enhancing tool accessibility. Exploratory work on machine learning methodologies was conducted to assess the potential for automated reduction of complex chemical schemes.

Black hole ringing in General Relativity and beyond
2025-11-27 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The black hole ringdown offers a powerful window into both astro- and fundamental physics. However, the construction of an accurate and reliable theoretical template for the interpretation of real data is crucial. In this seminar, I will discuss how ringdown modes respond to some ditinct physical key-effects.First, I will talk about the impact of a dynamical evolution of the black hole mass due to accretion or radiation. Then, I will present a parametrized framework to describe possible deviations from General Relativity in the ringdown spectrum of spinning black holes. Finally, I will explore how incomplete ringdown modeling can bias parameter estimation for massive black hole binaries observed by LISA, and assess the optimal degree of accuracy of the template that is required across parameter space.

Exploring the dark Universe with gravitational waves: new opportunities from the precision frontier
2025-11-27 16:00 - 17:00 | Anfiteatro Abreu Faro, Edifício Complexo Interdisciplinar do IST
95% of the Universe's current energy density does not interact with light. Furthermore, no light signal may arrive to us from the infancy of the Universe, when it was opaque. The first direct detection of gravitational waves in 2015 opened the door to overcome these two limitations. These waves may be produced from any violent-enough source of energy and traverse the early Universe almost unimpeded. In this colloquium I will describe how gravitational waves of different frequencies bring information from the invisible Universe, from primordial phase transitions to mergers of black holes of different sizes. I will emphasize which frequency bands are poorly covered today and show how quantum technologies in the precision frontier and precise astrophysical data may be the key to access them. This offers a unique opportunity to unveil the mysteries of the dark Universe!

Measurement Waiting Time Distributions as Probes of Dynamical Many-Body Quantum Phases Transitions
2025-12-02 12:00 - 14:00 | Sala V1.05 (piso) Edifício de Civil /Online
LinkThis thesis investigates waiting time distributions as post-selection-free probes of measurement-induced phase transitions in free fermion systems. We study the transverse-field XY chain under local particle number monitoring in both projective and decay unravelings, leveraging Gaussian state techniques and Monte Carlo wave function methods to efficiently simulate quantum trajectories. Through numerical simulations for chains up to L = 128 sites, we confirm the measurement-induced phase transition from a critical phase with S ∼ ln(l) entanglement scaling to an area-law phase at finite monitoring rate η. We employ spectral statistics of the entanglement Hamiltonian, including r-statistics from random matrix theory, revealing signatures consistent with the transition between ergodic and localized regimes. For waiting time distributions, we derive exact analytic expressions for the no-click survival probability from the maximally mixed steady state and compute first-jump time distributions. We find that waiting time distributions exhibit universal Poissonian behaviour at short times across all phases, with transition signatures emerging only at long times when survival probabilities decay to negligible values, effectively hiding the measurement-induced phase transition in rare-event tails. While derivatives of survival probability show non-analyticities at η agreeing with effective Hamiltonian spectral transitions, the dominance of short-time exponential decay poses experimental challenges. Our results demonstrate that although waiting time distributions remain post-selection-free and experimentally accessible, extracting clear measurement-induced phase transition signatures requires accessing rare long-time events, highlighting fundamental limitations and suggesting future directions toward refined measurement protocols, larger-scale simulations, and extensions to alternative unravelings such as quantum diffusion.

_Towards Quantum Sensor Networks
2025-12-02 13:00 - 15:00 | Online
Quantum sensor networks sets a framework for distributed sensing, aimed at retrieving information from spatially separated probes using quantum resources, enhancing precision beyond classical limits. This thesis develops tools for this framework and addresses fundamental questions arising from the distributed nature of these protocols. The first question concerns the information accessible in distributed scenarios. Focusing on functions locally accessible by each party, we introduce a privacy measure ensuring that only the target function’s information is revealed. We identify entangled states that guarantee privacy under specific encoding dynamics, and find robust private states resilient to qubit loss. We further extend these results to Hamiltonian dynamics, uncovering a mathematical structure linking private functions to private states and the nature of entanglement to the estimation of linear functions of local parameters. We proceed to employ concepts in geometry to analyze spatial quantum sensing, where sensor arrays probe an underlying field modeled by analytic functions. We transform a series of general problems into a description leveraging the linearity of the information in the distributed setting. We provide conditions for error-free sensor placements and extend previous approaches to general least-squares estimations, illustrating advantages of entangled strategies over local ones. Next, we integrate this into quantum networks, recognizing practical constraints, such as limited quantum resources, network topology, and sensor placement. We develop a general optimization framework for designing sensing protocols that minimize estimator variance. These methods translate sensing strategy design into linear, convex and nonconvex optimization problems, adapting to various network constraints and highlighting the impact of sensor positioning. Finally, we apply this to entangled atom gravimeters networks, establishing a proposal for the deployment of distributed gravitational field sensing, demonstrating potential for high-precision Earth interior modeling and offering a roadmap for the optimal construction and operation of quantum sensor networks, under minimal prior information.

Whole-Organism 3D Maps Reveal Parallel Self-Similar Vascular and Neural Networks with Divergent Murray-Like Exponents
2025-12-02 14:00 - 16:00 | Online
LinkComprehensive, cellular resolution reconstructions of embryonic vasculature and innervation have so far been constrained by the depth limits of optical clearing, the restricted fields-of-view of light-sheet microscopy and the labor-intensity of manual annotation. We present a unified, fully automated pipeline that converts routine serial H&E histology into organism-wide three-dimensional atlases of blood vessels and peripheral nerves. Convolutional neural networks, iteratively trained on a reduced set of manually attributed labels, achieve ≥93 precision and recall in semantic segmentation and a hybrid rigid-elastic registration restores anatomical continuity across thousands of sections; a TEASAR-based skeletonization yields graphs listing radii, lengths, and branching orders. Applied to four vertebrate embryos - Macaca mulatta at Carnegie stages 33 and 40, Mus Musculus at E11 and Trachemys Scripta at G17, with the last three being matched in development - the method generates vasculature and innervation reconstructions at cellular resolution across whole organisms. Quantitative analysis shows that both networks are self-similar, with nearly constant Horton ratios for segment number, radius and length. Vascular branch points obey Murray’s cube law, whereas nerves follow a Murray-like relation with an exponent close to 2, consistent with axial-current conservation. The two macaque stages differ only by uniform scaling and mouse and turtle values overlap with the corresponding macaque. These atlases thus offer a quantitative reference for developmental and allometric studies, while the reliance on standard histology allows for prospective multi-omic integration.

Polarimetric Studies Galaxies
2025-12-02 15:30 - 17:00 | Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática) do IST
A tese "Estudos Polarimétricos de Galáxias" investiga o uso da fotopolarimetria para melhor compreender a composição, estrutura e propriedades físicas da poeira interestelar em galáxias. Foi aplicada uma análise polarimétrica detalhada a galáxias hospedeiras de supernovas (SNe), com focos na polarização interestelar (ISP), nas propriedades de extinção da poeira e no alinhamento de campos magnéticos. A tese discute métodos de observação, modelação de transferência radiativa e correções polarimétricas, contribuindo multi-lateralmente para um entendimento mais profundo da polarização induzida pela poeira nos ambientes intergalácticos. No meio interestelar, a luz pode ser polarizada por dispersão em grãos de poeira ou por absorção de poeira esferoide alinhada por um campo magnético externo. A polarização por dispersão ocorre quando a luz interage com partículas de poeira, sendo desviada de sua trajetória original. Quando grãos esferoides se alinham com um campo magnético a luz que com eles interage será selectivamente absorvida, resultando em polarização. A luz pode ser descrita como uma onda eletromagnética composta por duas componentes de campo eléctrico oscilando perpendicularmente à direcção de propagação. Num meio interestelar com poeira, essa luz pode sofrer absorção selectiva devido à orientação preferencial dos grãos de poeira. Num campo magnético externo, grãos alongados alinharão o seu eixo menor paralelamente a esse campo, a absorção será por isso maior para a componente do campo eléctrico paralela à direcção do eixo maior dos grão, perpendicular ao campo magnético. Como resultado a luz transmitida será polarizada paralelamente ao campo magnético. A luz absorvida, em comprimentos de onda ópticos e ultra-violeta, será depois emitida em infra-vermelho com polarização rodada 90o . Este efeito leva à polarização linear da luz que atravessa a poeira interestelar. A relação de Serkowski, amplamente utilizada para descrever a polarização interestelar, foi confirmada em várias regiões da amostra de galáxias estudada. Tal permitiu determinar com precisão o comprimento de onda de máxima polarização (λmax) e a razão entre extinção total (AV) e selectiva (EB-V), também chamada de "lei de extinção" (RV), parâmetros essenciais para compreender a interação entre a poeira e a radiação. A partir da caracterização da polarização no enquadramento de absorção por grãos alinhados, é ainda inferida a existência e orientação de campos magnéticos responsáveis pela organização da poeira interestelar. A polarização pode ser usada para inferir a estrutura do campo magnético em diferentes escalas, desde regiões próximas a estrelas individuais até grandes estruturas dentro de galáxias. Modelos teóricos e simulações foram usados para validar estas relações e entender melhor os processos físicos envolvidos. A tese também discute a influência do tamanho e composição dos grãos de poeira na polarização da luz. Diferentes populações de grãos podem resultar em variações nas curvas de polarização, grau e ângulo, observadas, afectando a interpretação das propriedades interestelares. A relação entre a polarização e a extinção interestelar é explorada em detalhe, com vista a melhorar a compreensão dos efeitos da poeira em medições astrofísicas. Foram feitas simulações para entender o impacto da poeira interestelar na polarização da luz. Usando um modelo geometricamente simples, uma fonte luminosa quasi-esférica emersa num perfil Gaussiano 3D, foram testadas poeiras com diferentes tamanhos e composições, incluindo misturas de silicatos, grafenos e hidrocarbonetos poliaromáticos. Estas simulações foram feitas recurrendo ao SKIRT, um programa de simulação de transferência radiativa baseada no método de Monte Carlo, que permite modelar a propagação da radiação em meios astrofísicos complexos, levando em conta efeitos como dispersão, absorção e reemissão da luz por grãos de poeira. Os resultados indicaram que a dependência do grau de polarização com o comprimento de onda depende não só do tamanho dos grãos como da espécie química. Estas simulações foram essenciais para a interpretação dos dados observacionais e distinção entre diferentes mecanismos de polarização. Como projecto paralelo foi também desenvolvido um protótipo de modelo computacional emulador de transferência radiativa, o EmulaRT. O objectivo deste modelo era reduzir o custo computacional de simulações de elevada qualidade, através da melhoria de simulações de baixa qualidade recorrendo para isso a técnicas de compressão e up-scaling. O EmulaRT usa uma rede neuronal de arquitectura auto-codificadora variacional e de-noising em conjunto com um método de inferência espacial Bayesiana aproximada. Os resultados preliminares foram positivos, no entanto verificou-se que a amostra de treino era enviasada, tendo a aplicação do protótipo ficado mais limitado do que inicialmente previsto. Na vertente observacional foram usados dados observacionais de calibração do instrumento FORS2 do Very Large Telescope (VLT), que permite a captura de imagens polarimétricas de alta resolução. De modo a tentar minimizar o impacto de efeitos de polarização interestelar e instrumental, foi desenvolvida uma sequência robusta de redução de dados polarimétricos do FORS2. Esta sequência de redução é iniciada por calibrações típicas: subtracção do viés de leitura electrónica, normalização de sensibilidade do detector e remoção de raios cósmicos. Seguem-se operações de separação e combinação de informação disposta em diferentes ficheiros, estimativa de e remoção de fluxo de fundo. Depois através de detecção de fontes no campo de observado e cruzamento com o catálogo Gaia, é feita fotometria a estrelas da Via Láctea de modo a produzir uma estimativa da polarização interesteral da Via Láctea na direcção de observação. Para a correção instrumental são aplicados mapas de polarização do FORS2 pré-existentes. Verificou-se que as estimativas para o ISP da Via Láctea são compatíveis com as observações do Planck, embora com diferenças notáveis no ângulo. Os presentes resultados confirmam a presença de padrões de ângulo de polarização devida a dispersão axisimétricos, em várias galáxias da nosssa amostra, sendo o efeito mais pronunciado nas bandas azuis. A dependência da polarização com o comprimento de onda seguiu duas tedências principais: uma curva em U ou um crescimento monótono. Essas relação são compatíveis com as previsões para grãos de grafite e silicatos, respectivamente. Da vertente de polarização devida a absorção por grãos de poeira alinhas, alguns mapas de ângulo de polarização revelaram alinhamento com os braços espirais das galáxias, reforçando modelos que preveem a orientação dos campos magnéticos galácticos toroidais. Noutros casos verificou-se também a presença de ângulos de polarização alinhados paralelamente com o eixo menor das galáxias, o que é compatível com campos magnéticos polares. Em média, os valores de RV apresentados nas regiões medianas e externas das galáxias foram semelhantes ao da Via Láctea, ~3.1, mas nalguns casos foram verificadas variações significativas nas transições braço / entre-braços. Essas variações manifestam os ambientes distintos, com diferentes propriedades de poeira, inerentes a esses dois tipos de estrutura. Da análise de RV na vizinhança dos locais onde ocorreram as supernovas (hóspedes das galáxias na nossa amostra) resultou que, à escala espacial estudada, não há diferença estatística entre essas regiões particulares e todas as restantes regiões das galáxias respectivas. Comparações estatísticas mostraram que a polarização e, em alguns casos, RV, variam significativamente entre diferentes galáxias. Isso sugere que fatores intrínsecos podem influenciar essas propriedades de maneira única em cada galáxia. Os resultados apresentados nesta tese, bem como a abordagem de investigação multi-lateral tida, contribuem para o aprofundamento do estudo da polarização interestelar e suas implicações na astrofísica. A combinação de observações fotopolarimétricas com modelação computacional avançada permitiu uma caracterização detalhada das propriedades da poeira em galáxias hospedeiras de supernovas e inferência sobre a possível presença e caracterização de campos magnéticos galácticos.

Relevance of electronic interactions at quasiperiodicity-driven localization transitions
2025-12-02 15:30 - 17:00 | Sala de Formação Avançada Piso 2 Pavilhão de Física/Online
LinkIn real materials, disorder can induce (Anderson) insulating phases. Notably, quasiperiodic modulations can also strongly affect wavefunction localization. As the quasiperiodic potential increases, single-particle states transition from delocalized to critical and finally to localized, with metal-insulator transitions distinct from those in disordered systems.The simplest model capturing this transition is the Aubry-André model, which features a remarkable duality between localized and delocalized states, recently shown to be a generic feature, but somehow hidden, near the transition.Recently, studies in quasiperiodicity were extended to 1D systems of interacting spinless fermions. Interestingly, such interactions were found to become irrelevant around the transition, with eigenstates following the hidden-duality scenario of the non-interacting limit.This project explores the effects of spinful interactions in quasiperiodicity-driven localization transitions, specifically, whether they become relevant, as in higher-dimensional disorder-driven transitions, or remain irrelevant, as in the spinless case. We aim to determine whether these transitions can always be described by a non-interacting theory or if spinful interactions alter their nature.To study the system's ground-state properties, we employ the Density Matrix Renormalization Group (DMRG), which determines many-body quantum states with polynomial complexity in system size.Our results show that spinful interactions are relevant, modifying the nature and critical properties of the quasiperiodicity-driven localization transition. Unlike the spinless case, excitations at criticality display interacting behavior.Additionally, we investigate the interaction-driven ordered transition in the spinless model. This analysis revealed a highly interacting critical point. Within the LL phase, the single-particle observable (OIPR) and the Luttinger parameter capture information of the same nature.

From flavored experiments to flavored phenomenology
2025-12-02 16:00 - 18:00 | Sala de seminários (2-8.3) piso 2 Edifício de Física
Several recent experimental results by ATLAS, CMS, LHCb and Belle II provide new tests of the Standard Model and probe new physics. I will focus on two of these: The branching fraction of the rare decay B_s->K0bar+K0 and CP asymmetries in B->J/psi+pi. Within the Standard Model, these observables are related to other decay rates and CP asymmetries through the approximate SU(3) flavor symmetry of the strong interactions. The measured B_s->K0bar+K0 violates three such relations at a level of about 3 sigma each. The measured A_CP(B->J/psi+pi) provide further testable predictions and help closing in on sub-percent precision in the extraction of sin(2 beta)

Characterization of the Dosimetry System in Terms of Hp(3) for Eye-Lens Dose Assessment
2025-12-03 09:00 - 11:00 | Sala V1.07 Pavilhão de Civil
This work presents the characterization of a thermoluminescence dosimetry system based on LiF:Mg,Cu,P (TLD-100H) detectors for the measurement of the personal dose equivalent, Hp(3), used in eye-lens monitoring. The study was carried out at the Laboratorio de Protec¸ ´ ao e Seguranc¸a Radiol ˜ ogica (LPSR) ´ of Instituto Superior Tecnico (IST) and the irradiations were carried out at the Laborat ´ orio de Metrologia ´ das Radiac¸oes Ionizantes (LMRI) of LPSR. A series of performance tests including linearity, repro- ˜ ducibility, energy dependence, and angular dependence were carried out as part of the type-testing of the detectors, in order to evaluate the system’s suitability for routine monitoring applications. The results demonstrated a linear response within the 0.1-10 mSv range, with good reproducibility in the same range, which encompasses typical occupational exposure levels. The energy dependence test, performed with N80, N100, 137Cs, and 60Co radiation qualities, showed variations within acceptable values set in international standards [1]. Angular dependence was the most relevant evaluation, confirming reliable response between -60◦ and +60◦ , consistent with International Electrotechnical Commission (IEC) requirements [1] as well as ±90◦ , provided certain experimental conditions (Source to Detector Distance (SDD) ≥ 2.5m and shift of the phantom) are considered. The final expanded uncertainty for the system, considering all influencing factors, was 33.63% (k = 2). Overall, the TLD-100H dosimetry system proved fit for purpose, i.e. suitable for individual eye-lens dose assessment.

Simulation-based optimization of the Depth-of-Interaction determination capability of a PET scanner
2025-12-03 11:00 - 13:00 | Online
Cancer encompasses over a hundred diseases characterized by the uncontrolled proliferation of abnormal cells. Proton therapy enables precise tumor targeting while minimizing damage to healthy tissue, yet its effectiveness depends on accurate proton range verification. Among the available methods, Positron Emission Tomography (PET) is preferred for providing real-time, three-dimensional imaging and dosimetric information during treatment. Incorporating depth-of-interaction (DoI) measurement in PET scanners improves spatial resolution and reduces parallax errors, particularly at the periphery of the scanner. This study aimed to optimize, using simulation-based methods, the DoI determination capability of a dual-ended readout PET detection module. The module was modeled using the ANTS3 simulation toolkit. It consisted of a Lutetium–yttrium oxyorthosilicate (LYSO) scintillator with a 3 × 3 mm² cross-section and 30 mm length, coupled to two Hamamatsu S14161-3050HS-08 Silicon Photomultiplier (SiPM) sensors. The scintillator was encapsulated with an Enhanced Specular Reflector (ESR) film. The model was validated using available experimental data on the DoI resolution, showing sufficient predictive power. The optimization conducted in this study improved the DoI resolution by about 54% and up to 86% at the center and edges of the scintillator, respectively, compared to the initial configuration. This improvement was achieved by introducing an optical grease coupling between the scintillator and the sensors, implementing scintillator encapsulation with Lambertian scattering, and using a higher-efficiency SiPM sensor. A case study was also conducted to analyze the effect of scintillator size on the module's DoI determination capability. Retro-reflector scintillator encapsulation was identified as a promising option for future investigation.

The Lunar Ionising Radiation Environment - a benchmark model
2025-12-04 09:00 - 11:00 | Online
A Geant4-based Monte Carlo application was developed to model the Galactic Cosmic Ray (GCR) induced radiation environment on the lunar surface. It was adapted from ESA’s detailed Mars Energetic Radiation Environment Model, incorporating lunar-specific geometry and regolith composition. The simulations use the Badhwar–O’Neill 2020 model to derive the GCR spectrum, reproducing it both in spectra and in solar modulation. Simulations successfully reproduced the expected GCR spectra and solar modulation trends for 2009 (solar minimum) and 2015 (solar maximum). The resulting primary and albedo Linear Energy Transfer (LET) spectra showed good agreement with CRaTER measurements aboard the Lunar Reconnaissance Orbiter, accurately capturing the observed spectral shapes. Comparisons with HZETRN calculations further confirmed consistent modeling of secondary particle production and transport. The simulation framework developed in this work establishes a reliable baseline for evaluating lunar radiation hazards and supports future analyses of shielding eWectiveness, habitat exposure, and astronaut dosimetry for both short and longduration missions.

Uma Abordagem Progressiva à Teoria da Relatividade Geral
2025-12-04 09:00 - 11:00 | Sala V1.01 (Piso 1 do Pavilhão de Civil) do IST
General Relativity is one of the most elegant and fundamental frameworks in modern physics, yet it remains difficult to access for students at the beginning of their studies. Existing literature in Portuguese is scarce and, in many cases, traditional presentations assume complex concepts without clear motivation, creating additional barriers to learning. This thesis proposes and analyzes a new didactic approach to Relativity, designed to guide the reader progressively and logically through its fundamental concepts. The approach is structured as a sequential narrative, where each result is derived from intuitive motivations and thought experiments, avoiding leaps in reasoning. The text is self-contained, includes detailed proofs, solved examples, and intermediate challenges, allowing each student to adapt the reading process to their own pace. Although it does not present the complete version of the final approach, this thesis gathers a condensed and optimized structure, emphasizing the points where it differs from traditional literature: original derivations of results, new motivations for established concepts, and a pedagogical integration between mathematical rigor and geometric intuition. The goal is to contribute to the construction of a more accessible, structured, and engaging learning path, which may serve as the basis for the future publication of a didactic book in both Portuguese and English.

Descriptive and Predictive Modeling of Chaos in Cold Atom Physics using Explainable Deep Learning
2025-12-04 11:00 - 13:00 | Sala V1.06 Pavilhão de Civil
Ultracold atom clouds display intricate dynamics that can appear chaotic and lack a comprehensive explanatory framework. This dissertation investigates photon bubble turbulence in a 85Rb atom cloud confined in a magneto-optical trap, using recent advances in artificial intelligence to move beyond the limitations of classical modeling. Reduced-order methods and sparse regression provide interpretability but fail to capture long-term dynamics or generalize across regimes. To overcome these issues, deep learning models were developed, with a focus on convolutional autoencoders for reconstructing and analyzing atom cloud images. Results showed that these architectures consistently outperformed classical baselines, even in lowdimensional latent spaces, demonstrating the ability of convolutional representations to extract physically meaningful features. Latent space analysis revealed that the apparently chaotic turbulence is underpinned by compact structures, suggesting a simple order to chaos. Classification experiments showed that detuning values, determined by laser frequencies in the trap, can be reliably inferred from images, exposing discriminative features tied to light–atom interactions. Explainability was introduced through Grad-CAM, linking classification decisions to density structures in the clouds. The findings confirmed two dynamical regimes, stable and turbulent, separated by a phase transition, with further evidence of a transitional regime near resonance. Overall, explainable deep learning emerges as a powerful framework for predictive and descriptive modeling of ultracold atom systems, while also deepening our understanding of turbulence, phase transitions, and light–atom coupling.

Assessment of the potential of radiosensitizers to improve the efficacy of Radiation Therapy
2025-12-04 13:30 - 15:00 | Sala de Formação Avançada Piso 2 Pavilhão de Física
Cancer is a disease characterized by uncontrolled growth of cells, with breast cancer being one of the most common types, predominantly affecting women. Among the available therapeutic modalities, radiotherapy stands out as one of the most widely used, although it presents limitations due to irradiation of healthy tissues. In this context, the use of radiosensitizing particles has been extensively investigated, aiming to enhance the dose delivered to the tumor while reducing side effects in surrounding tissues.In this study, breast cancer cells were incubated with different concentrations of gold nanoparticles and subsequently irradiated with a clinical X-ray beam (6 MV) and a Cobalt-60 gamma rays beam at various dose points. Immediate biological effects were assessed through fluorescence assays, analysing DNA damage, lipid metabolism alterations, and reactive oxygen species production. Late effects were quantified by clonogenic assays, enabling the construction of survival curves based on the linear-quadratic model. Additionally, gold nanoparticles were incorporated into a radiotherapy treatment plan for a breast cancer patient to evaluate the potential clinical impact of this strategy.The results demonstrated a significant radiosensitizing effect of gold nanoparticles, leading to a substantial reduction in cell survival, particularly under clinical X-ray irradiation. It was also observed that including these radiosensitizers in treatment planning contributes to reduced doses to organs at risk, increasing the likelihood of tumor control.

Testing general relativity with the ringdown of gravitational-wave observations
2025-12-04 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Gravitational waves provide a unique opportunity to test gravity and probe the nature of astrophysical sources. With hundreds of binary coalescences detected by LIGO and Virgo, general relativity continues to stand as a successful theory of gravity. The loudest event to date, GW250114, offered a direct probe of the remnant’s Kerr nature by constraining multiple ringdown modes. In contrast, the second loudest signal, GW230814, exhibits a ringdown damping time shorter than predicted by general relativity. Simulations indicate that such deviations can arise from missing physics in waveform models or noise artefacts, suggesting no evidence for a breakdown of general relativity. In this talk, I will present analyses of recently observed gravitational-wave signals and discuss the prospects for testing fundamental physics with next-generation detectors.

Modelling the accretion-ejection flow around the supermassive black hole at the centre of the Milky Way
2025-12-04 16:00 - 18:00 | Sala V1.01 (Piso 1 do Pavilhão de Civil) do IST/Online
LinkOver the past decade, the study of compact objects has undergone substantial progress, with increasing focus on Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy and the closest of such objects to Earth. Due to its proximity, Sgr A* serves as an exceptional laboratory for relativistic astrophysics and general relativity. A major advancement in this field was achieved in 2022, when the Event Horizon Telescope (EHT) Collaboration released the first reconstructed image of Sgr A*’s immediate environment, enabling stronger constraints to be placed on state-of-the-art models.The primary objective of this Master’s thesis is to reproduce, through analytical models, the observed spectrum, EHT image, and polarization quantities of Sgr A*'s close environment, using the general relativistic ray-tracing code GYOTO. The work performed with GYOTO has provided valuable insights into the impact of relativistic effects on the resulting spectra and synthetic images of the disk–jet plasma.In this study, a new analytic disk + jet model is introduced, designed to reproduce both the characteristics of the observed spectrum, and the imaging observables reported by the EHT. An extensive exploration of the parameter space was conducted to identify the most influential parameters. Focus on optimizing the fit, while maintaining computational efficiency, was maintained throughout the project too. Although early simulations were affected by errors in the jet's density profile, these have since been resolved, resulting in a fully operational thick-disk + parabolic-jet model.

Plasma optical emission signal characterisation in Laser-Induced Breakdown Spectroscopy
2025-12-10 14:00 - 16:00 | Sala P3 (Piso 1 do Pavilhão de Matemática) do IST
The interaction of high-intensity laser pulses with a sample can result in the formation of a short-lived plasma. From the deexciation of the plasma, we can extract information about the chemical composition of the target using a spectrometer. This technique is known as Laser-Induced Breakdown Spectroscopy (LIBS).LIBS has attracted growing attention in different areas and applications for its ability to perform real-time, on-site and non-destructive elemental analysis across a wide range of materials. Nevertheless, its analytical performance is often limited by significant signal variability and reduced reliability.In this work, the plasma optical emission signal was successfully characterised under the influence of various experimental conditions by studying their effect on signal intensity and measurement variability. The analysis was conducted on a dedicated test bench and is structured into two main sections: plasma generation and plasma optical emission collection. The main results showed that, for ultrashort pulse durations at pulse energies close to the breakdown threshold, the signal intensity varies linearly. Regarding the focusing conditions, the analysis revealed the existence of two maxima, and a slight defocus was shown to improve plasma generation. Concerning signal collection, an optimal magnification that maximizes the collected emission was found. Additionally, the impact of the chromatic focal shift was verified and the isotropic nature of the plasma emission was demonstrated.

Disquisitions on the cosmological principle: Non-trivial realisations with some phenomenological consequences
2025-12-11 14:30 - 16:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The Cosmological Principle is one of the pillars of the standard model of cosmology and it is commonly realised in a trivial way with homogeneous SO(3)-scalars. I will discuss several scenarios where the matter sector realises the Cosmological Principle in a non-trivial manner by resorting to combinations of spacetime and internal symmetries. These scenarios include the effective field theory of fluids and solids (as well as their dual formulations), but more general setups based on e.g. vector fields with internal symmetries. A natural consequence of some of these scenarios is the appearance of a second helicity-2 mode in the cosmological perturbations that produces oscillations of gravitational waves with distinctive signatures. I will also discuss some intriguing realisations that occur on shell and lead to the possibility of having preferred directions in an exactly isotropic background universe.

Charting QCD jet evolution in extreme conditions
2025-12-12 15:00 - 17:00 | Online
In ultra-relativistic particle collisions, such as those performed at RHIC and LHC, quarks and gluons (partons) can be scattered with large transverse momenta and subsequently evolve into collimated sprays of hadrons known as jets. Jets are the experimental proxies for the hard scattered partons, convoluting both their perturbative and non-perturbative Quantum Chromodynamics (QCD) evolution. Depending on the collision system, the outgoing partons can either traverse what we actually call a “QCD vacuum”, as in deep inelastic scatterings (DIS) or proton-proton collisions, or a new, highly complex state of matter - the quark-gluon plasma (QGP), produced in heavy-ion collisions (HICs). This medium evolves concurrently with the hard partons, further convoluting HIC jets with QGP-induced effects.Our research aims to use jet substructure to disentangle these effects and probe QCD across different environments and energy scales. We employ substructure-based jet selections in electron-proton DIS to enhance sensitivity to non-perturbative effects, moving towards constraining currently existing phenomenological models to describe hadronization. Furthermore, a detailed characterization of jet quenching, i.e. the modification of jets in the presence of a QGP, has the potential to unlock a comprehensive tomographic description of the QGP. We explore novel jet substructure observables based on energy correlations to quantify jet quenching across angular scales.

Cosmological gravitational particle production: Scalars and fermions
2025-12-16 16:00 - 18:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
Particle production in the Early Universe is one of the cornerstones of modern cosmology and plays an important role in dark-matter phenomenology. In this talk, I will discuss the gravitational production of scalars and fermions during inflation. For scalars, I will compare Bogolyubov coefficient and Starobinsky stochastic approaches, showing that they only agree in the limit of infinitely long inflation. High-scale inflation is very efficient in particle production, leading to constraints on the existence of free, light, and stable scalars: such particles are viable only if their masses are below the eV scale or if the reheating temperature is in the GeV range. For fermions, I will show how the production efficiency depends on the particle mass, which is generated via the Yukawa coupling and sensitive to the corresponding scalar field value. Scalar fields can experience large quantum fluctuations during inflation, driving the average field to the Hubble scale and above. Thus, fermions can be very heavy during inflation, enhancing particle production. This mechanism can be the leading source of right-handed neutrinos, if they gain a Majorana mass from the Yukawa coupling to a singlet scalar.

Spacetime Grand Unified Theory
2026-01-06 16:30 - 18:00 | DF Seminar Room (2-8.3), 2nd floor of Physics Building
The Standard Model of particle physics is derived from the free Dirac Lagrangian from first principles. All known fermionic particle species plus three right handed neutrinos are obtained from ideals of an 8-dimensional Clifford algebra, with the Standard Model gauge symmetries arising uniquely as the rotations of Dirac spinors in 8-dimensional spacetime. Triality originates the strong force and three particle families, with family rotations connected to external transformations. Lorentz and gauge transformations are unified while avoiding the Coleman-Mandula theorem, with chirality stemming from orientation invariance in 8-dimensional spacetime.

_Flexible triboelectric nanogenerators for a self-charging system in mobile electronics
2026-01-13 13:30 - 15:00 | Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST
Triboelectric nanogenerators (TENGs) have emerged as versatile and scalable solutions for mechanical energy harvesting and self-powered sensors in wearable systems and smart textiles. By converting low-frequency biomechanical movements into usable electrical energy, TENGs show great potential for applications in sustainable electronics, health monitoring, and human– machine interfaces. However, developing materials and fabrication processes that combine high performance, flexibility, environmental stability, and scalability remains a challenge. This thesis investigates the use of graphene-based materials and aqueous-phase processing techniques for the fabrication of flexible, textile-compatible TENGs integrated into self-powered sensor platforms. Special emphasis is placed on sustainable manufacturing methods, such as printing and solution-based processing, as well as the development of graphene electrode solutions suitable for integration into flexible and textile technologies. In the first part, aqueous graphene solutions were used to fabricate TENGs through simple and scalable methods, resulting in devices with promising electrical performance and good stability. In the second stage, graphene electrodes were directly printed onto textiles, enabling their conformable integration into garments. These devices demonstrated reliable performance under bending and repeated mechanical deformation, proving effective for real-time biomechanical monitoring. In the third phase, multimodal triboelectric sensors were developed and embedded in smart textiles, capable of detecting different types of human motion—such as extension, bending, and sliding—within a single device architecture. This multimodal capability was achieved through strategic textile structural design combined with a wireless data transmission system. Overall, this work contributes to the advancement of smart textiles and sustainable wearable electronics by proposing eco-friendly graphene-based TENGs produced through scalable methods, with potential applications in energy harvesting and physiological monitoring.
