Inflationary Consistency Conditions and Shift-Symmetric Cosmologies

Abstract

The UV-sensitivity of the slow-roll conditions of Inflation requires stabilization of the inflaton field. One way to realize this, is through an (approximate) shift-symmetry. In this thesis, we review the necessary background of inflation and subsequently study the consequences of a shift-symmetry in this context. In the decoupling limit of gravity, such a symmetry is non-linearly realized by the Goldstone boson of spontaneously broken time translations, leading to consistency conditions among correlation functions which can be obtained in a number of ways. We derive these consistency conditions using the wavefunction and all results are verified using Ward identities. In the presence of gravity, the shift-symmetry gives rise to a new residual symmetry for which we find the corresponding adiabatic mode. This shift-symmetric adiabatic mode is non-linearly realized by the scalar curvature perturbation and hence also leads to consistency conditions.