Generation of hypermagnetic helicity and leptogenesis in early universe

TL;DR

This paper explores how hypermagnetic helicity and lepton asymmetry evolve in the early universe, revealing their roles in baryogenesis and the generation of the observed baryon asymmetry through hypermagnetic fields and lepton dynamics before the electroweak phase transition.

Contribution

It introduces a scenario where hypermagnetic helicity and lepton asymmetry interplay to produce the baryon asymmetry, emphasizing the importance of hypermagnetic fields in leptogenesis.

Findings

Hypermagnetic helicity evolution is linked to lepton asymmetry growth.

The scenario supports baryogenesis with hypermagnetic fields near maximum helicity.

Sphaleron transitions are negligible in this leptogenesis model.

Abstract

We study hypermagnetic helicity and lepton asymmetry evolution in plasma of the early Universe before the electroweak phase transition (EWPT) accounting for chirality flip processes via inverse Higgs decays and sphaleron transitions which violate the left lepton number and wash out the baryon asymmetry of the Universe (BAU). In the scenario where the right electron asymmetry supports the BAU alone through the conservation law $B/3 - L_{eR}=const$ at temperatures $T>T_{RL}\simeq 10~TeV$ the following universe cooling leads to the production of a non-zero left lepton (electrons and neutrinos) asymmetry. This is due to the Higgs decays becoming more faster when entering the equilibrium at $T=T_{RL}$ with the universe expansion, $\Gamma_{RL}\sim T> H\sim T^2$ , resulting in the parallel evolution of the right and the left electron asymmetries at $T<T_{RL}$ through the corresponding Abelian anomalies in SM in the presence of a seed hypermagnetic field. The hypermagnetic helicity evolution proceeds in a self-consistent way with the lepton asymmetry growth. The role of sphaleron transitions decreasing the left lepton number turns out to be negligible in given scenario. The hypermagnetic helicity plays a key role in lepto/baryogenesis in our scenario and the more hypermagnetic field is close to the maximum helical one the faster BAU grows up the observable value , $B_{obs}\sim 10^{-10}$.