Stellar disruption of axion miniclusters in the Milky Way

Abstract

Axion miniclusters are dense bound structures of dark matter axions that are predicted to form in the postinflationary Peccei-Quinn symmetry breaking scenario. Although dense, miniclusters can easily be perturbed or even become unbound by interactions with baryonic objects such as stars. Here, we characterize the spatial distribution and properties of miniclusters in the Milky Way (MW) today after undergoing these stellar interactions throughout their lifetime. We do this by performing a suite of Monte Carlo simulations which track the miniclusters’ structure and, in particular, accounts for partial disruption and mass loss through successive interactions. We consider two density profiles—Navarro-Frenk-White (NFW) and power-law (PL)—for the individual miniclusters in order to bracket the uncertainties on the minicluster population today due to their uncertain formation history. For our fiducial analysis at the solar position, we find a survival probability of 99% for miniclusters with PL profiles and 46% for those with NFW profiles. Our work extends previous estimates of this local survival probability to the entire MW. We find that towards the Galactic Center, the survival probabilities drop drastically. Although we present results for a particular initial halo mass function, our simulations can be easily recast to different models using the provided data and code (github.com/bradkav/axion-miniclusters). Finally, we comment on the impact of our results on lensing, direct, and indirect detection.