Axion cooling of neutron stars. II. Beyond hadronic axions

Abstract

We study the axion cooling of neutron stars within the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) model, which allows for tree level coupling of electrons to the axion and locks the Peccei-Quinn charges of fermions via an angle parameter. This extends our previous study [Phys. Rev. D 93, 065044 (2016)] limited to hadronic models of axions. We explore the two-dimensional space of axion parameters within the DFSZ model by comparing the theoretical cooling models with the surface temperatures of a few stars with measured surface temperatures. It is found that axions masses ma ≥ 0.06 to 0.12 eV can be excluded by x-ray observations of thermal emission of neutron stars (in particular by those of Cas A), the precise limiting value depending on the angle parameter of the DFSZ model. It is also found that axion emission by electron bremsstrahlung in neutron star crusts is negligible except for the special case where neutron Peccei-Quinn charge is small enough, so that the coupling of neutrons to axions can be neglected.

Quantum chromodynamics axion in a hot and magnetized medium

“…Axions have also been associated with the anomalous stellar cooling problem [13,14], including neutron stars [15][16][17]. This is because axions could be produced in hot astrophysical plasmas and, thus, could take part of the energy transport in stellar objects.…”

Gaia and the use of White Dwarfs as Advanced Physics laboratories

“…Axions with the properties described here not only would perturb the cooling of white dwarfs but they would also modify in a subtle way the evolution of other kind of stars. An extensive review can be found in Giannotti et al, (2017), while Sedrakian (2019) provides a recent analysis of the cooling by DFSZ axions of the neutron star in Cas A. Here only the two more restrictive tests are presented.…”

The axion-baryon coupling in SU(3) heavy baryon chiral perturbation theory

“…As a consequence of its (model-dependent) coupling to standard model particles, the axion of course also couples to composite particles such as mesons or baryons. One possible method of estimating constraints on the axion decay constant (or equivalently its mass) rests upon this coupling to baryons, in particular to nucleons, namely through nuclear bremsstrahlung processes in stellar objects [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] (see also the overviews [4,33,52,53]). The leading order aN coupling has been derived several times since the early days [23,35,[54][55][56].…”