UC Irvine

The primary focus of this work is to explore the implications of dark matter models in which dark matter is light and interacts with the standard model quarks. In Chapter 2 we consider dark matter coupling to the quarks as a vector current interaction for two distinct cases. In the first case we take dark matter to be a new spin-1 vector particle which decays into standard model particles, and in the second case we take dark matter to be a Dirac fermion which annihilates into standard model final states. We then impose constraints on these models by comparing the resulting photon signatures of dark matter annihilation/decay to the background diffuse emission and to future observations of the dwarf spheroidal galaxy Draco. Similarly, in Chapter 3 we again consider dark matter as a sub-GeV Dirac fermion and impose model constraints by examining its photon signature that results from the decay of its standard model final states. However, in this case we take the method of dark matter communication to the standard model to be through an axial-vector interaction (as opposed to a vector-like current). In both cases, we obtain constraints on the models by comparing the estimated photon signals to current and future observations, and show that the axial-vector DM portal is significantly more conducive to photon production for lighter forms of dark matter than a pure vector-like portal; establishing itself as a prime candidate for indirect detection probes with significant discovery reach.

Then in Chapter 4 we slightly change gears by considering dark matter coupling to quarks in the early universe. We explore a nonstandard cosmology in which the strong coupling constant evolves in the early Universe, triggering an early period of QCD confinement at the time of dark matter freeze out. We find that depending on the nature of the interactions between the dark matter and the Standard Model, freeze out during an early period of confinement can lead to drastically different expectations for the relic density, allowing for regions of parameter space which realize the correct abundance but would otherwise be excluded by direct searches.