Events

An effective-one-body model for intermediate-massratio black hole binaries

Mon, 02 Nov 2026 09:29:49 +0000

Thursday, 5th of November, 2026 from 2:30 p.m. to 4 p.m.

DF Seminar Room (2-8.3), 2nd floor of Physics Building

Intermediate-mass-ratio binaries are the least modelled sources by state-of-the-art waveform models, as their regime is not covered by numerical relativity, nor within the reach of gravitational self-force results. I will present an optimistic view of bridging the gap between the comparable-mass and the extreme-mass-ratio regimes by means of the effective-one-body (EOB) approach.

The EOB model I will introduce is currently limited to nonspinning and quasicircular binaries, and is based on the incorporation of high-order analytical information, without any calibration. It reaches a striking agreement with both the highest-mass-ratio simulations available within the SXS catalog and with the 1st-order post-adiabatic self-force model 1PAT1 for extreme-mass-ratio configurations. This result represents a promising route to build waveform models for intermediate-mass-ratio binaries only using analytical information.

Structural Order, Crystallinity, and Processing Effects in Organic Semiconducting Systems

Fri, 02 Oct 2026 08:48:58 +0000

Friday, 13th of November, 2026 from 9:30 a.m. to noon

Online

External link

Organic photovoltaic devices have attracted significant interest as lightweight, flexible, and solution-processable renewable-energy technologies. Their performance is strongly influenced by the morphological organization of the active layer, which affects charge photogeneration, transport, recombination, and collection processes. Understanding how specific structural and processing-related characteristics influence device behavior therefore remains an important topic within organic electronics.

This thesis investigates the influence of highly ordered interfaces, crystallinity, and processinginduced morphological modifications on the optoelectronic behavior of organic semiconducting systems through the study of deliberately simplified and well-defined model structures. In this context, three complementary research topics were investigated. The first research topic investigated the influence of crystal-crystal interface formation in highly ordered rubrene-based systems, revealing enhanced conductivity and charge transport associated with crystalline interfacial effects.

The second study explored the incorporation of a rubrene single-crystal donor within planar heterojunction organic solar cells, demonstrating efficient photovoltaic generation at crystalline donor/acceptor interfaces and providing insight …

Fifth Forces across Cosmic Scales: From Primordial Perturbations to Compact Stars

Wed, 30 Sep 2026 14:40:26 +0000

Friday, 20th of November, 2026 from 2 p.m. to 4 p.m.

Anfiteatro PA-3 (Piso -1 do Pavilhão de Matemática) do IST

Scalar fields coupled to matter mediating fifth-force interactions are ubiquitous in extensions of General Relativity. Reconciling their cosmological relevance with local gravity constraints requires either a weak coupling or a screening mechanism suppressing the force in dense environments.

This thesis investigates scalar-mediated fifth forces across two regimes: the unscreened early universe and the screened interiors of compact stars. In the cosmological regime, we study Early Coupled Quintessence, a model where a light scalar field mediates a fifth force stronger than gravity between dark matter particles during radiation domination, enhancing density perturbation growth with a characteristic goldenratio rate.

We implement the corresponding background and perturbation equations in the CLASS Boltzmann code and perform the first Markov chain Monte Carlo analysis of its parameter space, combining cosmic microwave background, supernovae, baryon acoustic oscillation, and big bang nucleosynthesis data. We confirm and quantify a fundamental degeneracy between the coupling strength and the redshift …