Axion in an External Electromagnetic Field

TL;DR

This paper explores how external electromagnetic fields can enhance axion interactions with photons, potentially increasing axion-related processes and energy losses in astrophysical environments.

Contribution

It provides a detailed analysis of axion-photon interactions in external fields, revealing field-induced enhancements and their astrophysical implications.

Findings

External fields remove suppression of axion processes.

Strong catalysis of axion-photon interactions occurs.

Potential new energy loss mechanisms in astrophysics.

Abstract

We investigate the effective interaction of a pseudoscalar particle with two photons in an external electromagnetic field in the general case of all external particles being off the mass shell. This interaction is used to study the radiative decay $a \to \gamma \gamma$ of the axion, a pseudoscalar particle associated with the Peccei-Quinn symmetry, and the crossing channel of photon splitting $\gamma \to \gamma a$. It is shown that the external field removes the suppression associated with the smallness of the axion mass and so leads to the strong catalysis of these processes. The field-induced axion emission by photon is analyzed as one more possible source of energy losses by astrophysical objects.