Dark Matter Minihalos from Primordial Magnetic Fields

Abstract

Primordial magnetic fields (PMF) can enhance baryon perturbations on scales below the photon mean free path. However, a magnetically driven baryon fluid becomes turbulent near recombination, thereby damping out baryon perturbations below the turbulence scale. In this Letter, we show that the initial growth in baryon perturbations gravitationally induces growth in the dark matter perturbations, which are unaffected by turbulence and eventually collapse to form $10^{-11}-10^3\ M_{\odot}$ dark matter minihalos. If the magnetic fields purportedly detected in the blazar observations are PMFs generated after inflation and have a Batchelor spectrum, then such PMFs could potentially produce dark matter minihalos.