Observational constraint on axion dark matter in a realistic halo profile with gravitational waves

Abstract

Axions are considered as a potential candidate of dark matter. The axions form coherent clouds, which can delay and amplify gravitational waves (GWs) at a resonant frequency and produce secondary GWs following a primary wave. All GWs detected so far from compact binary mergers propagate in the Milky Way halo, which is composed of axion dark matter clouds, resulting in the production of the secondary GWs. The properties of these secondary GWs depend on the axion mass and its coupling with the parity-violating sector of gravity. In our previous study, we have developed a search method optimized for the axion signals and obtained a constraint on the coupling that was approximately ten times stronger than the previous best constraint for the axion mass range, [1.7×10-13,8.5×10-12] eV. However, the previous search assumed that dark matter was homogeneously distributed in the Milky Way halo, which is not realistic. In this paper, we extend the dark matter profile to a more realistic one called the core Navarro-Frenk-White (NFW) profile. The results show that the previous study's constraint on the axion coupling is robust to the dark matter profile.