BEGIN:VCALENDAR VERSION:2.0 PRODID:-//linuxsoftware.nz//NONSGML Joyous v1.4//EN BEGIN:VEVENT SUMMARY:Nonlinear echoes from black holes in Einstein-Maxwell-scalar theor y DTSTART:20250515T143000Z DTEND:20250515T160000Z DTSTAMP:20260805T182810Z UID:f9bced53-0249-4cb2-a67e-7a0bc8fdc0f1 SEQUENCE:1 CREATED:20250509T142123Z DESCRIPTION: The post-merger portion of the gravitational wave emitted in a binary coalescence encodes precious information about the structure of t he remnant. While in the case of a black hole in General Relativity the si gnal is described by a standard ringdown\, when considering different obje cts\, or alternative theories of gravity\, new features might emerge. In t his context an interesting possibility is the appearance of echoes. While they are generally studied for exotic compact objects\, it has recently be en found that they might arise also for black holes in the Einstein-Maxwel l-scalar extension to General Relativity. Indeed\, in a particular region of the parameter space\, this theory admits hairy black hole configuration s whose effective potential under scalar or gravitational perturbations fe atures cavity-like structures\, where radiation can be trapped and echoes can be generated. In a recent work\, carried out in collaboration with Mar co Melis\, Robin Croft and Paolo Pani\, we computed the quasi-normal frequ encies of such black hole solutions\, for radial and axial modes. Furtherm ore\, by performing simulations of the spherical collapse of scalar wave p ackets\, 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 nonli nearities 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 he ad-on collision process with the aim of investigating whether echoes are p reserved in such a scenario\, or they are quenched by other dynamical effe cts. LAST-MODIFIED:20250509T142123Z LOCATION:DF Seminar Room (2-8.3)\, 2nd floor of Physics Building URL:http://df.vps.tecnico.ulisboa.pt/en/events/nonlinear-echoes-from-black -holes-in-einstein-maxwell-scalar-theory/ X-ALT-DESC;FMTTYPE=text/html:

The post-merger po rtion of the gravitational wave emitted in a binary coalescence encodes pr ecious information about the structure of the remnant. While in the case o f a black hole in General Relativity the signal is described by a standard ringdown\, when considering different objects\, or alternative theories o f gravity\, new features might emerge. In this context an interesting poss ibility is the appearance of echoes.

While they are generally st udied for exotic compact objects\, it has recently been found that they mi ght arise also for black holes in the Einstein-Maxwell-scalar extension to General Relativity. Indeed\, in a particular region of the parameter spac e\, this theory admits hairy black hole configurations whose effective pot ential under scalar or gravitational perturbations features cavity-like st ructures\, 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 s uch black hole solutions\, for radial and axial modes. Furthermore\, by pe rforming simulations of the spherical collapse of scalar wave packets\, we have been able to observe the presence of echo patterns in the time-domai n behavior of the scalar field\, even in the regime where nonlinearities a re significant.

In this talk I will present the results of our s tudy and discuss our follow-up project\, in which we will simulate the hea d-on collision process with the aim of investigating whether echoes are pr eserved in such a scenario\, or they are quenched by other dynamical effec ts.

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