Abstract:
In this thesis I study the physics of the early universe, speci cally in ation and the subsequent reheating process. In ation was proposed in the early 1980s to solve observational problems in the present day universe by introducing a very early period of near-exponential growth and has become a standard assumption in cosmology although its exact mechanism is not known. In the rst part of this thesis I describe the general dynamics of a single canonically coupled in aton with a fourth order polynomial potential. This model can produce an in ationary spectrum consistent with a wide range of observations. However, there are possible observations that it would not explain and constraints from planned experiments may have the ability to rule it out. This has implications for the overall in ationary paradigm: next generation experiments may rule out the most general renormalizable in ationary potential. The second part concerns the transition from in ation to big bang nucleosynthesis, known as reheating. This phase is important as it can a ect the details of the in ationary power spectrum and the present dark matter abundance. In simple models, the universe is dominated by a nearly-homogeneous in aton condensate when in ation ends. In some models, self interactions or couplings to other particles can quickly disrupt this condensate or lead to quick reheating. There are other models in which this does not happen and in ation can be followed by a long period in which the universe is dominated by an oscillating in aton condensate. I study the slow gravitational growth of perturbations in this condensate and its eventual breakup into isolated overdensities. I show that this growth is well described by the Schr odinger-Poisson equations, describe a code that solves them and use it to do the rst simulations of nonlinear perturbations in this phase.