Formation and mass growth of axion stars in axion miniclusters
  We study the formation and the subsequent mass growth of axion stars inside
axion miniclusters. Numerically solving the Schr\"odinger-Poisson equations
with realistic initial conditions we find that the axion stars exhibit similar
properties to solitonic cores in ultralight bosonic dark matter halos in terms
of their radial density profiles and large-amplitude oscillations. A merger of
two axion stars confirms a previously found empirical law for the mass of the
merged axion star. Monitoring the axion star masses over time, we observe a
mass growth consistent with the mass increase of Bose stars in the kinetic
regime reported by Levkov et al., confirming that the mass evolution of axion
stars can be understood in terms of wave condensation. Based on this result, we
predict a saturation of mass growth in relation to the minicluster mass
consistent with the core-halo mass relation previously found for ultra-light
bosonic dark matter halos.
