On the Schwinger effect during axion inflation

TL;DR

This paper refines the understanding of the Schwinger effect during axion inflation by incorporating non-collinear electric and magnetic fields and scale-dependent damping, leading to significantly different predictions for gauge field production.

Contribution

It introduces a new framework for modeling Schwinger pair production during axion inflation, accounting for non-collinear fields and scale-dependent effects, improving accuracy over previous models.

Findings

Energy densities of gauge fields can differ by over an order of magnitude from previous estimates.

The new model provides a more accurate description of gauge field damping during axion inflation.

Incorporating non-collinear fields and scale dependence significantly impacts physical predictions.

Abstract

Pair-creation of charged particles in a strong gauge-field background - the renowned Schwinger effect - can strongly alter the efficiency of gauge-field production during axion inflation. It is therefore crucial to have a clear understanding and proper description of this phenomenon to obtain reliable predictions for the physical observables in this model. In the present work, we revisit the problem of Schwinger pair production during axion inflation in the presence of both electric and magnetic fields and improve on the state of the art in two ways: (i) taking into account that the electric- and magnetic-field three-vectors are in general not collinear, we derive the vector decomposition of the Schwinger-induced current in terms of these fields and determine the corresponding effective electric and magnetic conductivities; (ii) by identifying the physical momentum scale associated with the pair-creation process, we incorporate Schwinger damping of the gauge field in a scale-dependent fashion in the relevant equations of motion. Implementing this new description in the framework of the gradient-expansion formalism, we obtain numerical results in a benchmark scenario of axion inflation and perform a comprehensive comparison with earlier results in the literature. In some cases, the resulting energy densities of the produced gauge fields differ from the old results by more than one order of magnitude, which reflects the importance of taking the new effects into account.