Recombination era magnetic fields from axion dark matter

TL;DR

This paper proposes a novel mechanism for generating magnetic fields during the recombination era, driven by axion Bose-Einstein condensates inducing vorticity in baryons, resulting in seed magnetic fields on galactic scales.

Contribution

It introduces a new Harrison-like mechanism linking axion condensates to magnetic field generation, surpassing previous second-order perturbation methods in magnitude.

Findings

Magnetic fields of order 10^{-23} G are generated on galactic scales.

The mechanism produces stronger seed fields than existing second-order perturbation theories.

Generated fields can serve as seeds for further magnetic amplification processes.

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 $\sim 10\,{\rm kpc}$ and have a magnitude of the order of $B\sim10^{-23}\,{\rm G}$ 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.