The axion-electron coupling $g_{ae}$ is a generic feature of nonhadronic 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 nonrelativistic 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.

• Received 23 April 2021
• Accepted 4 June 2021

DOI:https://doi.org/10.1103/PhysRevD.103.123024

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society