Revisiting axion-electron bremsstrahlung emission rates in astrophysical environments

TL;DR

This paper refines the calculation of axion-electron bremsstrahlung emission rates in astrophysical environments, providing a general formula applicable to various plasma conditions and axion masses, with implications for stellar bounds.

Contribution

It introduces a comprehensive formulation for axion-electron bremsstrahlung emission rates valid across different plasma degeneracies and axion masses, improving previous approximations.

Findings

Approximate emissivity calculations agree within 10% of exact results in red giants.

The new formulation extends stellar bounds to massive axions.

Validated the accuracy of previous approximations in astrophysical contexts.

Abstract

The axion-electron coupling $g_{ae}$ is a generic feature of non-hadronic axion models. This coupling may induce a variety of observable signatures, particularly in astrophysical environments. Here, we revisit the calculation of the axion-electron bremsstrahlung and provide a general formulation valid for a non-relativistic plasma with any level of degeneracy and for any axion mass. We apply our result to the Sun, red giant stars and white dwarfs. In particular, we prove that the approximations used to evaluate the axion emissivity in red giants agree with the exact result within $10\%$, comparable with other uncertainties in these studies. In addition, this prescription allows the red giant and white dwarf bounds to be extended to massive axions.