On the prospects of thermalization of axion-SU(2) inflation

TL;DR

This paper investigates whether gauge field interactions in axion-$SU(2)$ inflation models can lead to thermalization during inflation, analyzing parameter space and effects of gauge field vacuum expectations.

Contribution

It provides criteria for sustained thermalization in axion-$SU(2)$ inflation and explores the impact of gauge field VEVs on inflation dynamics.

Findings

Cold inflation regime is prevalent in the parameter space.

Thermalization is possible with non-zero gauge field VEVs.

Analysis includes dynamically generated gauge field VEVs.

Abstract

Axion inflation models coupled to a gauge sector via a Chern-Simons term exhibit an array of interesting phenomenology including a chiral gravitational wave spectrum and primordial black hole production. They may also provide a useful mechanism for generating lepton asymmetry. The possibility to embed this class of models in UV-finite theories and their intriguing, testable, signatures make for a compelling candidate for early acceleration. Due to the Chern-Simons coupling, gauge modes may undergo a finite tachyonic growth during which non-linearities become important. Naturally, this raises the question of whether such (self) interactions can lead to thermalization during inflation. We provide a set of useful criteria for sustained thermalization in an axion-$SU(2)$ model and chart the parameter space of the model accordingly. We find that the cold inflation regime constitutes a very significant fraction of the parameter space. Our analysis accounts for a initially vanishing as well as non-zero gauge field vacuum expectation value (VEV). We also consider the possibility of a dynamically generated VEV.