Constraining Light QCD Axions with Isolated Neutron Star Cooling

TL;DR

This paper investigates how light QCD axions influence neutron star cooling, using observational data to constrain axion properties without assuming they are dark matter.

Contribution

It introduces a novel method to constrain light QCD axions by analyzing their impact on neutron star thermal evolution and cooling patterns.

Findings

Axion fields can significantly alter neutron star cooling behavior.

Existing neutron star data can exclude certain axion parameter ranges.

The analysis does not depend on axions being dark matter.

Abstract

The existence of light QCD axions, whose mass depends on an additional free parameter, can lead to a new ground state of matter, where the sourced axion field reduces the nucleon effective mass. The presence of the axion field has structural consequences, in particular, it results in a thinner (or even prevents its existence) heat-blanketing envelope, significantly altering the cooling patterns of neutron stars. We exploit the anomalous cooling behavior to constrain previously uncharted regions of the axion parameter space by comparing model predictions with existing data from isolated neutron stars. Notably, this analysis does not require the light QCD axion to be the dark matter candidate.