Beyond standard models in cosmology (In French)

TL;DR

This paper explores theories beyond standard models in cosmology, focusing on cosmic strings and modified gravity models like Galileon to address fundamental physics limitations and dark energy phenomena.

Contribution

It advances the study of cosmic strings by incorporating full particle physics models and examines novel modified gravity theories related to the Galileon model.

Findings

Enhanced understanding of cosmic string formation with complete particle physics models

Development of new modified gravity theories related to the Galileon model

Potential explanations for dark energy phenomena

Abstract

The current description of fundamental interactions is based on two theories with the status of standard models. The electromagnetic and nuclear interactions are described at a quantum level by the Standard Model of particle physics, using tools like gauge theories and spontaneous symmetry breaking by the Higgs mechanism. The gravitational interaction is described on the other hand by general relativity, based on a dynamical description of space-time at a classical level. Although these models are verified to high precision in the solar system experiments, they suffer from several theoretical weaknesses and a lack of predictive power at the Planck scale as well as at cosmological scales; they are thus not viewed anymore as fundamental theories. As its phenomenology involves both these extreme scales, cosmology is then a good laboratory to probe theories going beyond these standard models. The first part of this thesis focus on cosmic strings, topological defects forming during the spontaneous symmetry breaking of grand unified theories in the early universe. I show especially how to study these defects while taking into account the complete structure of the particles physics models leading to their formation, going beyond the standard descriptions in terms of simplified toy-models. The second part is devoted to the construction and the examination of different theories of modified gravity related to the Galileon model, a model which tries in particular to explain the dark energy phenomenology.