Evolution of the Primordial Axial Charge across Cosmic Times

TL;DR

This paper studies how the axial charge decays in a hot electron-photon plasma, revealing a faster decay rate than previously thought, which impacts theories of leptogenesis and cosmic magnetogenesis.

Contribution

It demonstrates that the axial charge decay rate is first order in the fine-structure constant and significantly larger than earlier estimates due to infrared divergence effects.

Findings

Decay rate is proportional to α m_e^2 / T

Decay rate is much faster than previous estimates

Infrared divergences regularized by environmental effects

Abstract

We investigate collisional decay of the axial charge in an electron-photon plasma at temperatures 10 MeV - 100 GeV. We demonstrate that the decay rate of the axial charge is first order in the fine-structure constant $\Gamma_{\rm flip}\propto \alpha m_{e}^{2}/T$ and thus orders of magnitude greater than the naive estimate which has been in use for decades. This counterintuitive result arises through infrared divergences regularized at high temperature by environmental effects. The decay of axial charge plays an important role in the problems of leptogenesis and cosmic magnetogenesis.