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Non-cold dark matter imprint on cosmology

par Decant, Quentin
Président du jury Tytgat, Michel
Promoteur Lopez Honorez, Laura
Publication Non publié, 2023-09-29

Thèse de doctorat

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Résumé :

By now there is a substantial amount of evidence pointing towards the existence of dark matter (DM), which makes about 83% of the matter content in the universe. Despite massive experimental and theoretical efforts, there is no indisputable detection in astroparticle experiments to date. However, DM is an essential ingredient in the process of cosmological structure formation, thanks to which information on its properties can be gathered. In this thesis, we focus on so called non-cold dark matter (NCDM) models, especially those where the DM is produced with a non-negligible kinetic energy. The latter give to DM free-streaming which can impede the formation of structures, thereby leaving a visible imprint on several cosmological observables. In this thesis we first studied two NCDM scenarios beyond standard thermal warm dark matter (WDM). We filled the gaps present in the literature and confronted those scenarios to present-day observations. The first studied NCDM scenario considers the Freeze-in and superWIMP production mechanisms, both giving rise to Feebly Interacting Massive Particles as DM particles. Generic constraints on the model parameters are derived by recasting the Lyman-α forest flux observations in three different ways. Additionally, a particular realization of these mechanisms, namely within a top-philic mediator model, was chosen for a more detailed study. In that framework, special attention was paid to the cases with a significant interplay between the Freeze-in and superWIMP mechanisms, as well as to the case of Freeze-in by scatterings. The second NCDM scenario considered in this thesis was the case of NCDM production via primordial black hole (PBH)evaporation. The phase-space distribution of the DM was for the first time used as input for the Boltzmann code CLASS. This enabled to perform a precise determination of the bounds coming form the Lyman-α forest flux power spectrum. With these, we could confirm that the total abundance of light DM can not arise from evaporating PBH during a PBH-dominated era. After having used present-day available observations to constrain NCDM models, the focus shifts towards the future, specifically towards the potential detection of the 21cm power spectrum by the Hydrogen Epoch of Reionization Array (HERA) and what it can tell us about WDM. For this, the treatment of WDM in the simulator 21cmFAST has been updated. We also present the first steps towards a forecast on the bound of the WDM mass coming from HERA, using a Simulation-Based Inference approach, with Neural Ratio estimation as the method of choice.