Axion Minicluster Streams in the Solar Neighborhood.

Area of Science:

• Cosmology and Particle Physics
• Astrophysics and Dark Matter Research

Background:

• Post-inflationary QCD axion dark matter models predict small-scale structures called miniclusters.
• These miniclusters could hinder direct axion detection experiments due to their small size and density.
• Stellar encounters are known to tidally strip mass from dark matter structures, forming tidal streams.

Purpose of the Study:

• To investigate if stellar tidal stripping of miniclusters rescues prospects for direct axion detection.
• To determine the impact of tidal streams on the local dark matter density relevant for experiments.
• To explore observational signatures that could distinguish between different axion cosmological scenarios.

Main Methods:

• Simulations and theoretical modeling of minicluster evolution under stellar tidal forces.
• Analysis of dark matter density profiles in the solar neighborhood considering tidal stream contributions.
• Investigation of the spectral line shape of axion signals within these stream-dominated environments.

Main Results:

• Stellar stripping maintains local dark matter density at 70%-90% of the average local density.
• The solar neighborhood's dark matter is expected to be dominated by debris from numerous overlapping tidal streams.
• Axion signals in these streams exhibit a spiky line shape, deviating from the standard smooth Maxwellian distribution.

Conclusions:

• Tidal stripping by stars prevents axions from remaining bound in unobservably small miniclusters, preserving detection prospects.
• The predicted spiky spectral line shape offers a unique observational signature to differentiate between pre- and post-inflationary axion cosmologies.
• This work highlights the importance of considering astrophysical environments when interpreting dark matter detection experiments.