Gauge-preheating and the end of axion inflation

TL;DR

This paper investigates how axion inflation models can efficiently transfer energy to gauge fields during preheating, with implications for early universe dynamics and observable signatures.

Contribution

It demonstrates that preheating can be highly efficient in axion inflation with gauge couplings, including in axion monodromy models, and explores the effects on oscillons formation.

Findings

Preheating can transfer all inflaton energy to gauge fields within a few oscillations.

Gauge fields end preheating in an unpolarized state due to rescattering.

Coupling strength influences oscillon creation in axion monodromy models.

Abstract

We study the onset of the reheating epoch at the end of axion-driven inflation where the axion is coupled to an Abelian, $U(1)$, gauge field via a Chern-Simons interaction term. We focus primarily on $m^2\phi^2$ inflation and explore the possibility that preheating can occur for a range of coupling values consistent with recent observations and bounds on the overproduction of primordial black holes. We find that for a wide range of parameters preheating is efficient. In certain cases the inflaton is seen to transfer all its energy to the gauge fields within a few oscillations. In most cases, we find that the gauge fields on sub-horizon scales end preheating in an unpolarized state due to the existence of strong rescattering between the inflaton and gauge-field modes. We also present a preliminary study of an axion monodromy model coupled to $U(1)$ gauge fields, seeing a similarly efficient preheating behavior as well as indications that the coupling strength has an effect on the creation of oscillons.