Global charge conservation in the symmetric phase of the early Universe

TL;DR

This paper investigates how anomalous effects and perturbative processes in the early Universe's symmetric phase influence charge conservation, revealing that hypermagnetic helicity mainly converts into Chern-Simons numbers rather than matter-antimatter asymmetry.

Contribution

It introduces a method to compute the evolution of hypermagnetic helicity and Chern-Simons numbers considering non-equilibrium sphaleron effects, confirming global charge conservation.

Findings

Hypermagnetic helicity predominantly converts into Chern-Simons numbers.

Only a small fraction (10^{-3}) of hypermagnetic helicity converts into matter-antimatter asymmetry.

Global charge involving B+L, h_B, and N_CS,w is conserved.

Abstract

In the Standard Model at high temperatures, anomalous effects contribute to the violation of baryon number ($B$) and lepton number ($L$), separately, while $B-L$ remains conserved. There are also corresponding changes in the helicity of the hypermagnetic field ($h_B$) and the Chern-Simons numbers of the non-Abelian gauge fields ($N_{\rm CS,w}$ and $N_{\rm CS,s}$). In this study, we investigate a baryogenesis process in the symmetric phase of the early Universe by taking into account the Abelian and non-Abelian anomalous effects as well as the perturbative chirality-flip processes of all fermions. We calculate the time evolution of all relevant physical quantities, including the asymmetries of all fermions and the Higgs, as well as $h_B$ and $N_{\rm CS,w}$. We present a method to compute the latter, for which it is crucial to consider the minute departure from equilibrium of the sphaleron processes. We then verify explicitly the conservation of a global charge, involving the total matter-antimatter asymmetry $B+L$, the hypermagnetic helicity $h_B$ and $N_{\rm CS,w}$, the existence of which had been inferred earlier. In particular we show that, in the scenario that we study, an initial $h_B$ decays mostly to $N_{\rm CS,w}$, with only $10^{-3}$ conversion ratio into $B+L$ asymmetry.