Théorie

Black hole perturbations in modified gravity

General relativity can be tested at many scales using various physical systems. A particularly interesting probe is the study of the ringdown phase of a binary black hole merger, during which the newly-formed black hole emits gravitational waves at given frequencies called its quasinormal modes. Such modes depend heavily on the theory of gravity underlying the solution and can thus be used to test GR and put constraints on modified gravity theories.

New ideas on quenching and detecting BH rotational superradiances

In this talk I’ll discuss two recent results on BH superradiance: first, I will describe how BH photon superradiance is typically quenched by interactions of the photon cloud with the ambient electrons. Second, I will explain how an axionic cloud may impact the CMB if it decays into low energy photons which quickly heat and ionise the surrounding medium to Mpc scales.

Cosmic String Interpretation of NANOGrav Pulsar Timing Data and its impact on Cosmic Archaeology with Gravitational Waves

The NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension Gμ∈(4×10^{−11},10^{−10}) at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers.

A numerical approach to stochastic inflation and primordial black holes

Primordial black holes are a dark matter candidate, which may originate from strong perturbations created during inflation. These perturbations can be studied using the formalism of stochastic inflation. I present a numerical approach to this problem, where the stochastic dynamics is solved by generating a large number of random realizations. This makes it possible to go beyond analytical approximations and take into account additional effects such as backreaction between the perturbations and the background.

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