Searching for Dark Matter in the Early and Late Universe

Abstract

The particle nature of dark matter is a defining problem of modern particle physics, arguably the most blatant and most elusive sign of physics beyond the Standard Model. Over the past decades, it has also become a proving ground for diverse scientific collaboration, as a vast array of cosmological, astrophysical, tabletop, and underground probes are harnessed in tandem to address this puzzle. In the past several years, cosmology and astrophysics in particular have surged into prominence, and the ensuing influx of data have offered us new and exciting pathways to search for new physics.

In this dissertation we will present several fronts of progress, showcasing how observables from the early and late universe can uncover various facets of dark sector interactions: At the largest scales, we derive model-independent limits on the elastic scattering cross-section between baryons and dark matter using Cosmic Microwave Background data from the Planck satellite and measurements of the Lyman-alpha forest flux power spectrum from the Sloan Digital Sky Survey. At lower redshifts, we consider minimal extensions to the SM by new massive light relics, and forecast the significance at which these new particles, with different masses and temperatures, can be detected by upcoming Large-Scale Structure surveys. We then obtain state-of-the-art constraints from presently available cosmological data. Zooming in further, we illustrate the potential of Local Group dwarf galaxy shapes to elucidate dark matter substructure and self-interactions. We consider methods to infer 3D morphological information on Local Group dwarf spheroidals, and test the fitness of CDM+hydrodynamics simulations to the observed galaxy shapes. We find that the subpopulation of dwarf galaxies with high mass-to-light ratio reflects an oblate morphology, discrepant with simulations of CDM-sourced galaxies which are explicitly prolate. Finally, and closest to us, we analyze the implications of the robust Galactic Center gamma-ray Excess and prospects of forthcoming antideuteron experiments for annihilating dark matter, showcasing the phenomenology of two particle models in particular: one where Majorana fermion dark matter annihilates through a CP-violating Higgs portal, and one where Dirac fermion dark matter annihilates to kinetically-mixed dark photons.