Lepton asymmetries and primordial hypermagnetic helicity evolution

TL;DR

This paper investigates the evolution of hypermagnetic helicity during the electroweak phase transition, highlighting its potential primordial origin and implications for the development of galactic magnetic fields.

Contribution

It provides a comprehensive calculation of hypermagnetic helicity evolution, completing previous models and emphasizing the importance of primordial helicity in galactic magnetic field scenarios.

Findings

Hypermagnetic helicity density exceeds galactic magnetic helicity by many orders of magnitude.

Primordial magnetic fields are likely to be substantially helical.

The results impact models of galactic magnetic field evolution.

Abstract

The hypermagnetic helicity density at the electroweak phase transition (EWPT) exceeds many orders of magnitude the galactic magnetic helicity density. Together with previous magnetic helicity evolution calculations after the EWPT and hypermagnetic helicity conversion to the magnetic one at the EWPT, the present calculation completes the description of the evolution of this important topological feature of cosmological magnetic fields. It suggests that if the magnetic field seeding the galactic dynamo has a primordial origin, it should be substantially helical. This should be taken into account in scenarios of galactic magnetic field evolution with a cosmological seed.