Inflation : phenomenological study and LiteBIRD space mission preparation
- Authors
- Publication Date
- Sep 13, 2024
- Source
- HAL
- Keywords
- Language
- English
- License
- Unknown
- External links
Abstract
This thesis is devoted to the study of cosmological inflation, a phase of accelerated expansion in the early universe that remains speculative to this day. The central observable for this study is the cosmic microwave background (CMB), the oldest light still visible today, whose statistical study enables cosmological inference.We first approach the study from an experimental perspective, focusing on the preparation of the LiteBIRD satellite. Set to launch in the middle of the next decade, LiteBIRD will measure the large-scale polarisation of the CMB with unprecedented precision, allowing for stringent constraints on the presence of primordial gravitational waves generated during inflation. To achieve the required sensitivity and minimise systematic effects, we must ensure precise control of both the instrument and data analysis. As part of this effort, we have implemented the instrument model in a dedicated database, along with the tools necessary to produce key instrumental parameters. This includes generating quaternions that encode each detector's pointing and orientation information, as well as implementing beam models, bandpasses, the noise model, and the specification of the readout system. Furthermore, we have developed a complete pipeline for analysing the polarisation maps that LiteBIRD will deliver. We have tested this pipeline on realistic simulations of the instrument with various levels of complexity. The analysis pipeline consists of three stages. The first stage involves component separation to remove foreground contamination from the maps. We optimise an agnostic method that does not rely on prior knowledge of the foreground properties. The second stage focuses on estimating power spectra from the cleaned and masked maps. To this end, we have implemented and tested various unbiased and quasi-optimal methods. Finally, we assess the performance of different likelihood functions to infer cosmological parameters. In addition to constraining primordial gravitational waves, this analysis will enhance our understanding of the epoch of reionisation, which is due to the intense radiation from the first generation of stars.In the third section of the thesis, we focus on a phenomenological study of inflation, particularly on a model of inflation situated within a particle physics framework: the minimal supersymmetric model. In collaboration with cosmologists, theorists, and particle physicists, we demonstrate that the existing data from the Planck satellite are already precise enough that systematic errors in the model's predictions dominate the error budget in an inference context. These theoretical systematics arise from the non-inclusion of radiative corrections and an incomplete understanding of the end of inflation. We have included the necessary corrections and identified points in parameter space that satisfy both the observational constraints of particle physics (such as the Higgs mass and direct SUSY searches at the LHC) and cosmology (including the dark matter fraction in the universe and the properties of scalar perturbations as observed by Planck). Our work demonstrates the feasibility of unifying particle physics and cosmology descriptions within a single self-consistent model, paving the way for a comprehensive exploration of the inflationary MSSM or other high-energy physics models.
