Enhanced Disruption of Axion Minihalos by Multiple Stellar Encounters in the Milky Way

TL;DR

This paper demonstrates that multiple stellar encounters more effectively disrupt axion minihalos in the Milky Way than previously thought, significantly impacting axion dark matter detection strategies.

Contribution

It introduces a more accurate model of stellar disruptions by including multiple encounters and relaxation timescales, refining predictions of minihalo survival.

Findings

Stellar interactions reduce minihalo mass retention to ~30%.

Enhanced disruption increases axion density in inter-minihalo space.

Results suggest improved prospects for axion detection.

Abstract

If QCD axion dark matter formed post-inflation, axion miniclusters emerged from isocurvature fluctuations and later merged hierarchically into minihalos. These minihalos, potentially disrupted by stellar encounters in the Milky Way, affect axion detectability. We extend prior analyses by more accurately incorporating multiple stellar encounters and dynamical relaxation timescales, simulating minihalo orbits in the Galactic potential. Our results show stellar interactions are more destructive than previously estimated, reducing minihalo mass retention at the solar system to ~30%, compared to earlier estimates of ~60%. This enhanced loss arises from cumulative energy injections when relaxation periods between stellar encounters are accounted for. The altered minihalo mass function implies a larger fraction of axion dark matter occupies inter-minihalo space, potentially increasing the local axion density and improving haloscope detection prospects. This work highlights the significance of detailed modeling of stellar disruptions in shaping the axion dark matter distribution.