# Cosmological Spherical Collapse with Relativistic Hydrodynamics and Threshold for Primordial Black Hole Formation

Student thesis: Doc typesDocteur en Sciences

### Résumé

This work is devoted to the study of the gravitational spherical collapse of pressured matter in a cosmological background using the tools of numerical relativity. The thesis is divided into two parts.

In the first one, we investigate the universality of the critical collapse with respect to the matter type by considering the constant equation of state $\omega$ as a control parameter. It is shown numerically, in the cases the background is Minkowski or de Sitter, that the mass of the formed black hole, for sub-critical solutions, rescales in a power-law of $|\omega - \omega^*|$, where $\omega^*$ is the critical $\omega$, with an exponent independent of the matter type. For the full matter Friedmann-Lemaître-Robertson-Walker background, serious indications in favour of universality are exposed but some numerical noise from the Einstein-de Sitter outer boundary conditions prevents us to prove it completely.

The second part investigates the hypothesis that Dark Matter is made of Primordial Black Holes (PBH) by computing the critical delta at several moments of the post-inflationary thermal history of universe, when the equation of state knows some dips that favour their formation. The peaks in the PBH mass function are shown to be attenuated and shifted towards lower masses. These results seem to reject the initial hypothesis but the importance of the gauge choice is pointed out.
la date de réponse 2020 Anglais Universite de Namur FSR-FNRS Andre Fuzfa (Promoteur), Alexandre Mauroy (Président), Sebastien CLESSE (Jury), Christophe Ringeval (Jury) & Eric Gourgoulhon (Jury)

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