Axion assisted Schwinger effect

TL;DR

The paper demonstrates that a classical axion-like background can significantly enhance fermion pair production in strong electric fields, especially at high momenta, with potential implications for axion cosmology.

Contribution

It introduces the axion assisted Schwinger effect, showing how axion fields can amplify pair production rates and validates the result through invariance and anomaly reproduction.

Findings

Enhanced pair production rate at high momenta due to axion coupling

Invariance under field redefinitions and chiral anomaly reproduction

Potential implications for axion inflation and dark matter detection

Abstract

We point out an enhancement of the pair production rate of charged fermions in a strong electric field in the presence of time dependent classical axion-like background field, which we call axion assisted Schwinger effect. While the standard Schwinger production rate is proportional to $\exp(-\pi(m^2+p_T^2 )/E)$, with $m$ and $p_T$ denoting the fermion mass and its momentum transverse to the electric field $E$, the axion assisted Schwinger effect can be enhanced at large momenta to $\exp(-\pi m^2/E)$. The origin of this enhancement is a coupling between the fermion spin and its momentum, induced by the axion velocity. As a non-trivial validation of our result, we show its invariance under field redefinitions associated with a chiral rotation and successfully reproduce the chiral anomaly equation in the presence of helical electric and magnetic fields. We comment on implications of this result for axion cosmology, focussing on axion inflation and axion dark matter detection.