| Summary: | 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. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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