Gauge Field Amplification during Axion Inflation

Abstract

This thesis studies the interaction of different fields during inflation and resultant phenomenology at different scales. It particularly focuses on one of the most well motivated inflationary models, called Axion inflation. Axions are pseudo-scalars that possess the shift symmetry at least at the approximate level, which protects their potential from quantum corrections and elevates them as a strong inflaton candidate. However, in the particle inventory of UV complete theories, axion particles are abundant, which motivates studying axions as inflaton or spectator field during inflation. In this work, we study a chiral shift symmetric dimension-five operator arising naturally in any axion theory. Due to this coupling, the gauge field'Äôs dispersion relation is modified and one helicity of the gauge field is produced abundantly as a function of a dimensionless parameter proportional to speed of the axion. This breaks the parity conservation. Furthermore, this amplified gauge quanta inversely decays (ie. sources back) to scalar and tensor degrees of freedom via two-to-one way; hence, the sourced perturbations obey non-Gaussian statistics. These sourced modes leave unique imprints on cosmological observables such as : Chiral gravitational wave (GW) background, large tensor non-Gaussianity, non-zero TB and EB correlators, detectable GW background at interferometer scales and the production of primordial black holes.