Structure of Axion Miniclusters

Understand

The Peak-Patch algorithm is used to identify the densest minicluster seeds in the initial axion density field simulated from string decay.

• The fate of these dense seeds is found by tracking the subsequent gravitational collapse in cosmological $N$-body simulations.
• We find that miniclusters at late times are well described by NFW profiles, although for around 80\% of simulated miniclusters a single power-law density profile of $r^{-2.9}$ is an equally good fit due to the unresolved scale radius.
• Under the assumption that all miniclusters with an unresolved scale radius are described by a power-law plus axion star density profile, we identify a significant number of miniclusters that might be dense enough to give rise to gravitational microlensing if the axion mass is $0.2 \,\mathrm{meV}\lesssim m_a \lesssim 3\,\mathrm{meV}$.