UC San Diego

This dissertation contains works spanning several topics in cosmology and astrophysics. They are tied together by themes of dark matter and the Cosmic Microwave Background (CMB), but with a highly varied methodology spanning theory, data analysis, and hardware. Chapter 2 introduces a novel production mechanism for sterile neutrino dark matter involving multiple interacting sterile neutrinos. Chapter 3 presents a search for axion-like particle dark matter using the CMB telescope POLARBEAR. Finally, Chapter 4 describes the building and testing of the Small Aperture Telescope for the next-generation CMB experiment the Simons Observatory.