Description du sujet de thèse

All cosmological structures, from galaxies to planets, originate from the gravitational amplification of quantum vacuum fluctuations during an early phase of accelerated expansion of the universe known as inflation. This scenario elegantly explains the small density fluctuations observed in the cosmic microwave background and in the large-scale structure of our universe. It provides an ideal framework to explore the interaction between gravity and quantum physics.

Cosmological fluctuations are usually described by a semi-classical perturbative approach, which is valid in the regime of small-amplitude fluctuations. However, recent observations have revealed the presence of abnormally large density fluctuations, such as massive galaxy clusters in the very young universe, as well as several indications suggesting the existence of primordial black holes. These black holes, present in the universe well before the formation of the first stars, could account for dark matter.

The study of large fluctuations requires non-perturbative methods. The goal of the PhD thesis is to develop an effective stochastic framework that incorporates the backreaction of quantum fluctuations on the expansion dynamics of the universe, and to predict the mass distribution of primordial black holes, as well as the gravitational wave background we should expect from them.

Contexte de travail

The research work will be conducted under the supervision of Vincent Vennin (HDR) and Lucas Pinol, within team 20 “Cosmology and Gravitation” of the Physics Laboratory at the École Normale Supérieure in Paris.

Contraintes et risques

As this is purely theoretical work, no particular risks have been identified.