UC Irvine

Dark matter remains the foremost sign of particle physics beyond the Standard Model. Little is known about its microscopic properties, but there are compelling astrophysical and cosmological reasons to believe that it resides in a ``dark sector'' with its own forces, and with weak coupling to the Standard Model. One popular theory which may explain these dark matter interactions is known as the ``kinetic mixing portal'' wherein a ``dark photon'' of a new abelian gauge symmetry is induced to mix with the Standard Model photon, and thus to mediate interactions with the visible sector. In this dissertation we will examine the phenomenology of this theory. As dark matter travels through the galaxy it may scatter off of nuclei through dark photon exchange, losing enough energy to become gravitationally trapped and accumulate in astrophysical bodies. We propose and examine in detail a search for the dark photons radiated by this trapped population of dark matter in Chapters 2, 3, and 4, finding that there are viable regions of parameter space that cannot be probed by direct detection but would be amenable to discovery by this search. In Chapter 5 we perform a detailed calculation of the dark matter abundance in theories where dark matter annihilates through the kinetic mixing portal. We find that the reach of current dark photon search experiments are remarkably sensitive to the mass of the dark photon near resonance and place an absolute lower limit on the thermal relic parameters of scalar dark matter coupled to a dark photon.