Revealing the Structure of the Inflationary Landscape through Primordial non-Gaussianity

Abstract

In this thesis, we show how the structure of the landscape potential of the primordial Universe may be probed through the primordial density perturbations responsible for the origin of the cosmic microwave background anisotropies and the large-scale structure of our Universe. Isocurvature fields may have fluctuated across the barriers separating local minima of the landscape potential during inflation. We analyze how this process could have impacted the evolution of the primordial curvature perturbations. If the typical distance separating consecutive minima of the landscape potential and the height of the potential barriers are smaller than the Hubble expansion rate parametrizing inflation, the probability distribution function of isocurvature fields becomes non-Gaussian due to the appearance of bumps and dips associated with the structure of the potential. We show that this non-Gaussianity can be transferred to the statistics of primordial curvature perturbations. The type of non-Gaussian structure that emerges in the distribution of curvature perturbations cannot be fully probed with the standard methods of polyspectra; instead, the probability distribution function is needed. To substantiate our claims, we offer a concrete model consisting of an isocurvature perturbation with a sinusoidal potential and a linear derivative coupling between the isocurvature and curvature field. This result is generalized to arbitrary potentials and briefly studied beyond first-order perturbation theory. Finally, we undertake a study of primordial non-Gaussianity of the local type, where we use our results to reconstruct and constrain the shape of the landscape potential with the help of Cosmic Microwave Background observations by the Planck telescope and explore prospects for observable quantities in the Large-Scale Structure of our universe towards constraining its primordial statistics.