Estimate of the primordial magnetic field helicity

Abstract

Electroweak baryogenesis proceeds via changes in the non-Abelian Chern-Simons number. It is argued that these changes generate a primordial magnetic field with left-handed helicity. The helicity density of the primordial magnetic field today is then estimated to be given by $\sim 10^2{n}_b$ where $n_b\sim 10^{-6}$ /cm${}^3$ is the present cosmological baryon number density. With certain assumptions about the inverse cascade we find that the field strength at recombination is $\sim 10^{-13}$ G on a comoving coherence scale $\sim 0.1$ pc.

Comments: Several improvements; version accepted for publication in PRL