Extragalactic magnetic fields unlikely generated at the electroweak phase transition

TL;DR

This paper argues that magnetic fields from the electroweak phase transition are likely too weak to account for observed cosmic void magnetic fields unless they possess significant helicity, implying the need for alternative generation mechanisms.

Contribution

It demonstrates that electroweak-generated magnetic fields are insufficient unless they have substantial helicity, highlighting the necessity for new primordial helicity generation mechanisms.

Findings

Electroweak-generated fields are too weak without helicity.

Helicity produced during baryogenesis is too small to explain observations.

New mechanisms are needed to generate primordial magnetic helicity.

Abstract

In this letter we show that magnetic fields generated at the electroweak phase transition are most likely too weak to explain the void magnetic fields apparently observed today unless they have considerable helicity. We show that, in the simplest estimates, the helicity naturally produced in conjunction with the baryon asymmetry is too small to explain observations, which require a helicity fraction at least of order $10^{-14}-10^{-10}$ depending on the void fields constraint used. Therefore new mechanisms to generate primordial helicity are required if magnetic fields generated during the electroweak phase transition should explain the extragalactic fields.