Axion Miniclusters and Bose Stars

Abstract

Evolution of inhomogeneities in the axion field around the QCD epoch is studied numerically, including for the first time important non-linear effects. It is found that perturbations on scales corresponding to causally disconnected regions at $T\sim 1\mathrm{GeV}$ can lead to very dense axion clumps, with present density $ρ_a \ga 10^{-8}\,{\rm g \, cm^{-3}}$. This is high enough for the collisional $2a\to 2a$ process to lead to Bose--Einstein relaxation in the gravitationally bound clumps of axions, forming Bose stars.

12 pages plus 3 eps figures (available via e-mail: [email protected]), LaTeX, FERMILAB--PUB--93/066-A