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Long wavelength cosmological perturbations and preheating Zibin, James Peter

Abstract

This thesis is concerned with the evolution of long wavelength cosmological perturbations in the very early inflationary and post-inflationary stages of the universe. I first provide a thorough review of the relevent theoretical background. This material is presented in a completely original manner, with essentially all of the required results exposed together. Emphasis is made throughout on elucidating the physical meaning of the results. I next perform a study of a particular inflationary model for which there can be explosive growth of long wavelength perturbations due to the process of parametric resonance, and I try to determine whether the backreaction of small scale perturbations is sufficient to save the standard inflationary predictions. I conclude that, for certain parameter values, it is not. Then I describe in considerable detail general aspects of the evolution of long wavelenth modes. I provide a careful link between the evolution of a set of homogeneous background scalar fields, treated as a dynamical system, and the evolution of physical, long wavelength modes. I show that in general we expect several physical modes which cannot be gauged away, and whose evolution depends on the behaviour of the background system. In parametric resonance the resonance can be seen as the instability of a periodic orbit in the background phase space. Finally I demonstrate that another type of background instability, dynamical chaos, can similarly lead to the rapid growth of long wavelength modes.

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