Transient phenomena in the axion assisted Schwinger effect

TL;DR

This paper investigates transient particle production effects in fermions within an axion background, clarifying computational subtleties and regularization issues in Schwinger pair production scenarios involving external electromagnetic fields.

Contribution

It provides a detailed analysis of transient phenomena and addresses ambiguities in defining particles at intermediate times in axion-influenced Schwinger effect calculations.

Findings

Clarified the computation of transient effects in fermionic Schwinger production.

Highlighted the importance of UV regularization in axion backgrounds.

Resolved ambiguities in defining particles during intermediate times.

Abstract

Particle production induced by a time-dependent background is well understood as the projection of the time-evolved initial state onto a set of final states. While the asymptotic initial and final states are well defined in the usual way, the definition of particles and antiparticles at intermediate times in the presence of external fields is ambiguous. These external fields moreover induce divergences which require regularization. In this paper we clarify some subtleties in the computation of transient effects in physical quantities for fermions in a homogeneous axion background, including Schwinger production in background electromagnetic fields. The presence of the axion requires particular care as well as knowledge of the UV theory when regulating the theory and computing the vacuum contribution to the fermion energy.