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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/193152
Dark Matter and Massive Neutrinos: Cosmological Probes of Physics Beyond the Standard Model
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[eng] The overwhelming evidence for the existence of dark matter in the Universe, and the discovery of the neutrino masses, are striking indicators of the need for new physics beyond the ΛCDM and Standard Model paradigms. Dark matter (DM) constitutes 85 % of the matter in the Universe, but its fundamental nature remains a mystery. Moreover, the physical mechanism responsible for the neutrino masses is unknown. A complete theoretical framework – consistent with all observations – that incorporates a microscopic description of dark matter into the standard models of cosmology and particle physics, as well as an understanding of the origin and scale of the neutrino masses, is a key common goal. Cosmological observables are promising in this regard and can provide unique insights into the nature of these elusive particles. This thesis focuses on the synergy between cosmology and particle physics in answering these fundamental questions. To this end, I present examples of how upcoming measurements probing the high-redshift Universe can unveil new insights into the nature of dark matter and the complementarity between cosmological observations and terrestrial experiments in determining the neutrino mass hierarchy. The first part of the research presented in this thesis studies the signatures of non-gravitational DM interactions on cosmological observables. I compute the effects of DM decay and annihilation on the thermal and ionisation history of the Universe, and the imprint on the 21 cm line intensity mapping signal from the dark ages. I examine the potential to detect such a signature with forthcoming 21 cm line intensity mapping measurements, presenting forecasted constraints for both upcoming and next-generation experiments. Next, the effects of DM-baryon scattering in the post-recombination Universe are explored. In this work, I consider for the first time the direct contribution of such interactions on the baryon and dark matter temperature perturbations and the resulting evolution of cosmological density perturbations. In particular, I show that these contributions lead to a large enhancement of the baryon temperature power spectrum and a further suppression of matter clustering at small scales, which can alter both the amplitude and time evolution of the 21 cm signal from cosmic dawn and reionization. In the second part of this thesis, I look at the question of neutrino masses and the mass hierarchy from the lens of cosmology. Cosmological surveys provide the tightest constraints on the absolute mass scale of neutrinos, and are closing in on the minimum mass bound allowed under the inverted hierarchy. Using the latest results from global fits to neutrino oscillations experiments combined with cosmological constraints on the sum of the masses, I perform a Bayesian analysis to constrain the individual neutrino masses and evaluate the Bayesian Evidence for each of the neutrino mass orderings. The results show that current data provide strong Bayesian preference for the normal mass hierarchy, even under widely different prior assumptions, which has important implications for particle physics. Finally, I conclude the thesis with a summary of the key results and examine their relevance within the broader context of the field. Moreover, I discuss future prospects and potential avenues to follow up this work.
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SHORT, Kathleen. Dark Matter and Massive Neutrinos: Cosmological Probes of Physics Beyond the Standard Model. [consulta: 8 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/193152]