Naturally inflating on steep potentials through electromagnetic dissipation

TL;DR

This paper demonstrates that electromagnetic dissipation can enable natural inflation with steep potentials by slowing the axion through gauge field coupling, producing a quasi-scale invariant spectrum with large amplitude.

Contribution

It introduces a mechanism where gauge field coupling induces dissipation, allowing inflation on steep potentials in natural inflation models.

Findings

Gauge field quanta production slows the axion.

Inflation occurs despite steep potentials due to dissipation.

Perturbation spectrum is quasi-scale invariant but with large amplitude.

Abstract

In models of natural inflation, the inflaton is an axion-like particle. Unfortunately, axion potentials in UV-complete theories appear to be too steep to drive inflation. We show that, even for a steep potential, natural inflation can occur if the coupling between axion and gauge fields is taken into account. Due to this coupling, quanta of the gauge field are produced by the rolling of the axion. If the coupling is large enough, such a dissipative effect slows down the axion, leading to inflation even for a steep potential. The spectrum of perturbations is quasi-scale invariant, but in the simplest construction its amplitude is larger than $10^{-5}$. We discuss a possible way out of this problem.