Inflation: Connecting Theory with Observables

Abstract

Information about the very early universe can be accessed from observations of the cosmic microwave background (CMB) radiation and the later formation of large-scale structure (LSS) that are produced from cosmological perturbations of the early universe. The most developed theoretical explanation for the origin of these perturbations is the theory of inflation, in which the early universe undergoes a period of accelerated expansion, amplifying quantum fluctuations to macroscopic size, which act as the seeds for the CMB anisotropies and the cosmic web of the LSS. The work in this thesis aims to connect the theory of inflation to properties of these observables in a highly detailed way, suitable for future high-precision astronomical surveys. After some introductory review chapters, we begin with new research on a study of inflation from string theory, deriving an observably-large value of the tensor-to-scalar ratio, which had been previously difficult to achieve theoretically. The next study investigates the link between the observed CMB power asymmetry and non-Gaussianity, including a novel non-zero value for the trispectrum. Next we study soft limits of non-Gaussian inflationary correlation functions, focussing first on the squeezed limit of the bispectrum and then generalizing to soft limits of higher-point correlation functions, giving results valid for multi-fi eld models of inflation.