High energy problems in cosmology

In recent years, cosmological data has become a valuable tool in constraining models high energy particle physics. At the same time, explanations of the data often require new particles and fields beyond those of the standard model of particle physics. This thesis examines several areas of cosmology where high energy physics plays a crucial role. We will focus on the physics of inflation, reheating and dark matter and explain their sensitivity to high energy processes. New models of each of these phenomena are proposed and their consequences are studied. The models will be evaluated both on their merits as models of high energy physics and their ability to explain cosmological data.