Dark Matter Minihalos from Primordial Magnetic Fields

TL;DR

This paper explores how primordial magnetic fields can induce the formation of small dark matter minihalos by affecting baryon perturbations and their gravitational growth, even in turbulent conditions.

Contribution

It demonstrates that primordial magnetic fields can lead to the formation of dark matter minihalos in the mass range of $10^{-11}$ to $10^3$ solar masses, a novel mechanism linking magnetic fields to small-scale structure formation.

Findings

Primordial magnetic fields can induce baryon perturbations that gravitationally grow into dark matter minihalos.

Dark matter minihalos of mass $10^{-11}$ to $10^3$ solar masses can form due to magnetic field effects.

Magnetic fields from post-inflationary origins could produce observable dark matter minihalos.

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.