Probing axions with neutron star inspirals and other stellar processes

TL;DR

This paper explores how axions could mediate detectable forces between neutron stars, which can be observed through gravitational wave signals, providing a novel way to probe axion properties beyond traditional constraints.

Contribution

It introduces the idea that axion-mediated forces between neutron stars can be as strong as gravity and detectable via gravitational wave observations, expanding methods to test axion models.

Findings

Axion forces can be comparable to gravity between neutron stars.

Future LIGO observations can probe extensive axion parameter space.

Axion forces evade fifth force constraints due to sourcing only from dense objects.

Abstract

In certain models of a QCD axion, finite density corrections to the axion potential can result in the axion being sourced by large dense objects. There are a variety of ways to test this phenomenon, but perhaps the most surprising effect is that the axion can mediate forces between neutron stars that can be as strong as gravity. These forces can be attractive or repulsive and their presence can be detected by Advanced LIGO observations of neutron star inspirals. By a numerical coincidence, axion forces between neutron stars with gravitational strength naturally have an associated length scale of tens of kilometers or longer, similar to that of a neutron star. Future observations of neutron star mergers in Advanced LIGO can probe many orders of magnitude of axion parameter space. Because the axion is only sourced by large dense objects, the axion force evades fifth force constraints. We also outline several other ways to probe this phenomenon using electromagnetic signals associated with compact objects.