Dark and Light: Unifying the Origins of Dark and Visible Matter

Abstract

The Standard Model of particle physics can account for neither the dark matter dominating the universe's matter density, nor the baryon asymmetry that leads to the visible matter density. This dissertation explores models of new physics that connect dark matter to baryogenesis and can naturally account for the observed quantities of both types of matter. Special emphasis is given to models incorporating new weak-scale physics, as such models often predict signatures at present and upcoming experiments and can potentially be connected to solutions of the hierarchy problem. In one class of models we study, the dark matter abundance is determined by a dark matter asymmetry connected to the baryon asymmetry. In such models, the separate dark matter, baryon, and lepton number global symmetries observed today are individually broken at or above the weak scale and lead to mixing of dark matter and Standard Model fields in the early universe. This can happen generically, with dark matter-visible matter mass mixing induced by large background energies or moduli in the early universe, and can also arise at the electroweak phase transition. Mass mixing models of asymmetric dark matter can readily accommodate dark matter masses ranging from 1 GeV to 100 TeV and expand the scope of possible relationships between the dark and visible sectors. We also consider models of symmetric dark matter in which the annihilation of dark matter particles in the early universe generates the observed baryon asymmetry. This process, called “WIMPy baryogenesis”, naturally accommodates weak-scale dark matter and explains the observed dark matter density with only order-one couplings. WIMPy baryogenesis is a new model of baryogenesis at the weak scale, avoiding problems with high reheat temperatures in supersymmetric theories, and yielding observable consequences in ongoing and future experiments for some models