Evolution of the Primordial Axial Charge across Cosmic Times

Understand

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.