Primordial magnetogenesis before recombination

TL;DR

This paper proposes a primordial magnetogenesis mechanism before recombination based on known physics, generating extremely weak magnetic fields on small scales that are sustainable and comparable to existing theories on similar scales.

Contribution

It introduces a novel mechanism for seed magnetic field generation before recombination using photon fluctuations, producing smaller but sustainable fields on small scales.

Findings

Generated magnetic fields are of order 10^{-49} G on 10 kpc scale.

Fields are sustainable and not erased by resistive diffusion.

Compared to other theories, fields are weaker but on smaller scales.

Abstract

The origin of large magnetic fields in the Universe remains currently unknown. We investigate here a mechanism before recombination based on known physics. The source of the vorticity is due to the changes in the photon distribution function caused by the fluctuations in the background photons. We show that the magnetic field generated in the MHD limit, due to the Coulomb scattering, is of the order $10^{-49}$~G on a coherence scale of 10 kpc. We explicitly show that the magnetic fields generated from this process are sustainable and are not erased by resistive diffusion. We compare the results with current observations and discuss the implications. Our seed magnetic fields are generated on small scales whereas the main mechanisms studied in the literature are on scale bigger than 1 Mpc. However, compared to more exotic theories generating seed magnetic fields on similar scales, the strength of our fields are generally smaller.