Recombination era magnetic fields from axion dark matter

Abstract

We introduce a new mechanism for generating magnetic fields in the recombination era. This Harrison-like mechanism utilizes vorticity in baryons that is sourced through the Bose-Einstein condensate of axions via gravitational interactions. The magnetic fields generated are on the galactic scales $\sim 10\mathrm{kpc}$ and have a magnitude of the order of $B\sim 10^{-23}\mathrm{G}$ today. The field has a greater magnitude than those generated from other mechanisms relying on second order perturbation theory, and is sufficient to provide a seed for battery mechanisms.

Comments: 4 pages; v2: minor changes, references added