Observable predictions of generalised inflationary scenarios.

Abstract

Inflation is an early period of accelerated cosmic expansion, thought to be sourced by high energy physics. A key task today is to use the influx of increasingly precise observational data to constrain the plethora of inflationary models suggested by fundamental theories of interactions. This requires a robust theoretical framework for quantifying the predictions of such models; helping to develop such a framework is the aim of this thesis. We begin by providing the first complete quantization of subhorizon perturbations for the well-motivated class of multi-field inflationary models that possess a non-trivial field metric. In particular, the implications for the bispectrum of the Cosmic Microwave Background (cmb) are potentially very exciting. The subsequent evolution of perturbations in the superhorizon epoch is then considered, via a covariant extension of the transport formalism. We demonstrate appropriate matching between the subhorizon and superhorizon calculations. With the aim of developing intuition about the relation between inflationary dynamics and the evolution of cosmic observables, we investigate analytic approximations of superhorizon perturbation evolution. The validity of these analytic results is contingent on reaching a state of adiabaticity which we discuss and illustrate in depth. We then apply our analytic methods to elucidate the types of inflationary dynamics that lead to an enhanced cmb non-Gaussianity, both in its bispectrum and trispectrum. In addition to deriving a number of new simple relations between the non-Gaussianity parameters, we explain dynamically how and why different shapes of inflationary potential lead to particular observational signals. In addition to multiple scalar fields, candidate theories of high energy physics include many possible modifications to the Einstein{Hilbert action. We consider the observational viability of single field chaotic inflation with additional corrections as motivated by low energy effective string theory. These new ingredients allow for consistency of chaotic inflationary models that are otherwise in tension with observational data.