Axion effects in the stability of hybrid stars

TL;DR

This paper explores how axion fields, which violate charge-parity symmetry, influence the stability of massive hybrid neutron stars by affecting their phase transition properties, potentially aligning models with astrophysical observations.

Contribution

It introduces the role of axions in stabilizing hybrid neutron stars and demonstrates their impact on the deconfinement phase transition within the star's core.

Findings

Axions weaken the deconfinement phase transition.

Presence of axions stabilizes massive hybrid stars.

Results align with astrophysical constraints.

Abstract

We investigate the effects of including strong charge-parity (CP) violating effects through axion fields in the microscopic equation of state of massive hybrid neutron stars. We assume that their cores contain deconfined quark matter and include the effects of axions via an effective 't Hooft determinant interaction. The hadronic crusts are described using different approaches in order to make our results more general. We find that the presence of axions stabilizes massive hybrid neutron stars against gravitational collapse by weakening the deconfinement phase transition and bringing it to lower densities. This enables to reproduce hybrid neutron stars in agreement with modern astrophysical constraints.