Testing the Fundamental Properties of Dark Matter

Abstract

Although the existence of dark matter has been concretely established for decades, very little is known about the substance that makes up approximately 25% of the energy density and 85% of the matter density of the Universe. A dedicated experimental paradigm exists to test many viable candidate models of dark matter, but in the absence of decisive experimental signatures to guide the development of the field, it is crucial that all possible sources of data are utilized to constrain the dark matter theory space. This thesis discusses several new methods for gleaning information about the fundamental properties of different models of dark matter from various data sources. The first portion of this thesis investigates the phenomenology of some non-minimal dark sector models at neutrino facility fixed-target experiments. These experiments feature high-luminosity beams of particles that impinge upon a dense target, from which neutrinos (and possibly dark matter) can propagate downstream to a highly shielded detector. Data from several previous and ongoing experiments are used to place limits on well-motivated models of thermal-origin pseudo-Dirac dark matter. The second portion of this thesis focuses on alternatives to traditional dark matter models that feature new long-range forces or modifications to gravity in galactic dynamics. Although such models have already been challenged by results in galaxy clusters and cosmology, their behavior within galaxies may be an emergent property and therefore independent of the behavior of themodel at large scales. For the first time, data from photometric and astrometric stellar surveys in the Milky Way are used to differentiate between models with galactic dynamics dominated by cold dark matter halos and by new long-range forces, finding a distinct preference for cold dark matter. The final portion of this thesis studies direct detection of ultralight bosonic dark matter. If the mass of the dark matter is light enough, the dark matter is best understood as an oscillating classical field. This field is coherent on short timescales but decoheres stochastically on long timescales, which can have non-trivial effects on the discovery potential of direct detection experiments.