Leptogenesis in the Symmetric Phase of the Early Universe: Baryon Asymmetry and Hypermagnetic Helicity Evolution

TL;DR

This paper models the evolution of baryon asymmetry in the early universe's symmetric phase, considering hypermagnetic fields with a spectrum, and finds conditions under which the observed asymmetry can be generated.

Contribution

It introduces a continuous hypermagnetic helicity spectrum into leptogenesis calculations, providing new insights into BAU growth mechanisms in the early universe.

Findings

BAU growth increases with maximum wave number $k_{max}$.

Large initial right-handed electron asymmetry can lead to negative BAU.

Small initial asymmetry allows BAU to reach observed levels.

Abstract

We investigate the evolution of the baryon asymmetry of the Universe (BAU) in its symmetric phase before the electroweak phase transition (EWPT) induced by leptogenesis in the hypermagnetic field of an arbitrary structure and with a maximum hypermagnetic helicity density. The novelty of this work is that the BAU has been calculated for a continuous hypermagnetic helicity spectrum. The observed BAU $B_{obs} = 10^{-10}$ that can be in large-scale hypermagnetic fields satisfying the wave number inequality $k \leq k_{max}$ grows with increasing $k_{max}$. We will also show that the initial right-handed electron asymmetry $\xi_{eR}(\eta_0)$ used in our leptogenesis model as a free parameter cannot take too large values, $\xi_{eR}(\eta_0) = 10^{-4}$, because this leads to a negative BAU by the EWPT time. In contrast, a sufficiently small initial right-handed electron asymmetry, $\xi_{eR}(\eta_0)$, provides its further growth and the corresponding BAU growth from zero to some positive value,including the observed $B_{obs} = 10^{-10}$.