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138. R. Z. Ferreira: Primordial black holes and axions: a tale of (galactic and extragalactic) light20/12/2022, 14:30
Primordial black holes with asteroid-like masses (10^{14−18} kg) can still account for all the dark matter. In this talk, I will discuss a new indirect probe of PBH dark matter. I will show that axions with masses in the 0.1eV-MeV range can form in clouds around such PBHs, via superradiance, and ultimately decay, if coupled to photons. The decay products will contribute to the galactic or...
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20/12/2022, 14:45
The non-singular bouncing cosmology is an alternative paradigm to inflation, where the background energy density vanishes at the bounce point in the context of Einstein’s gravity. Therefore, the non- linear effects in the evolution of density fluctuations (δρ) may be strong in the bounce phase, which potentially provides a mechanism to enhance the abundance of primordial black holes (PBHs). We...
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20/12/2022, 15:00
In the recent years, our understanding of the galactic centre has grown rapidly with the joint efforts of large international collaborations like the GRAVITY, who detected infrared flares close to the innermost stable circular orbit (ISCO) of the supermassive black-hole at the galactic centre, and the Event Horizon Telescope (EHT), which recently published the first picture of a black-hole...
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20/12/2022, 15:15
We report the results of the first comprehensive study on the shadows of fundamental Kerr black holes with Proca hair. Some of these solutions show striking non-Kerr features, such as chaotic patterns, non- smooth shadow edges, and ghost shadows. We illustrate how fundamental photon orbits can help us understand some of these features. Nonetheless, a wide range of solutions where deviations...
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20/12/2022, 15:30
Gravitational waves provide a unique opportunity to test gravity in the dynamical and nonlinear regime. Here, we propose a parametrised test of general relativity that introduces generic deviations to the plunge, merger and ringdown stages of binary-black-hole coalescences. The novel feature of the model is that it can capture signatures of beyond-GR physics in the merger phase of black-hole...
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20/12/2022, 15:45
The coalescence of compact binaries and the gravitational waves produced in this process provide an unique view into gravity in its dynamical, nonlinear regime. Proeminent during a black-hole coalescence is the plunge-merger stage, when the black holes collide at a large fraction of the speed of light and around which the gravitational-wave luminosity peaks. How robust are the predictions of...
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