Stacie Moltner (The University of Texas at Austin)

"Constraining new physics with cosmological and astrophysical data"

Abstract: Dark matter (DM) accounts for approximately 85% of matter in the Universe, yet much is unknown about its fundamental properties beyond its gravitational interactions. In particular, our current understanding of DM interactions with the Standard Model (SM) of particle physics relies in part on placing constraints on model-dependent parameter spaces. Cosmological and astrophysical observations provide an abundance of data with which to constrain possible interactions between DM and the SM. In this defense I will discuss constraining DM-baryon interactions from both astrophysical and cosmological perspectives.

Part I investigates an alternative to the indirect detection search channels of DM annihilation and decay, in which a pseudoscalar DM particle is absorbed by a nucleus, resulting in nuclear excitation and the prompt emission of a photon through de-excitation. For carbon and oxygen in the Galactic Centre of the Milky Way, the de-excitation photon spectra are on the order of 10 MeV and could therefore be detected by gamma-ray telescopes. From existing COMPTEL data we provide current constraints on the DM-nucleus coupling as well as projections for future experiments AMEGO-X, e-ASTROGAM, and GRAMS. We find the absorption process to be very sensitive to the DM mass, and find that the future experiments considered would improve constraints by over an order of magnitude.

Part II investigates scattering between DM and helium and hydrogen in the early Universe, placing constraints on DM-helium scattering using Cosmic Microwave Background (CMB) data. We consider DM interactions with nucleons via scalar, pseudoscalar, and vector mediators, which would result in scattering with hydrogen and helium with cross sections that have a power-law dependence on the relative DM-baryon velocity. Three coupling scenarios are considered: DM coupling only to neutrons, only to protons, and equally to neutrons and protons. Using Planck 2018 data for CMB temperature, polarization, and lensing anisotropies, we place constraints on DM scattering with helium and hydrogen for DM masses between 10 keV and 1 TeV. For scenarios with both hydrogen and helium scattering, we find helium scattering dominates constraints for DM masses above the proton mass.