Strong backreaction of gauge quanta produced during inflation

TL;DR

This paper investigates how gauge quanta produced during inflation, influenced by axion dynamics and backreaction effects, affect the energy density oscillations and gravitational wave spectrum, revealing dependencies on coupling strength and potential slope.

Contribution

It introduces a toy model analyzing strong backreaction effects of gauge quanta during inflation, highlighting how coupling and potential slope influence energy density and gravitational waves.

Findings

Gauge quanta energy density oscillates quasiperiodically under strong backreaction.

Peak amplitude of energy density increases with steeper axion potential slope.

Strong coupling decreases the peak amplitude of gauge field energy density.

Abstract

During inflation an axion field coupled to a gauge field through a Chern-Simons term can trigger the production of gauge quanta due to a tachyonic instability. The amplification of the gauge field modes exponentially depends on the velocity of the axion field, which in turn slows down the rolling of the axion field when backreaction is taken into account. To illustrate how the strength of the Chern-Simons coupling and the slope of the axion potential influence the particle production, in this paper we consider a toy model in which the axion field is a spectator with a linear potential. In the strong backreaction regime, the energy density of the gauge field quasiperiodically oscillates. The steep slope of the axion potential linearly increases the peak amplitude of the energy density while the strong coupling linearly decreases the peak amplitude. Additionally, we calculate the energy spectrum of gravitational waves.