The Electroweak Vacuum Angle at Finite Temperature and Implications for Baryogenesis

TL;DR

This paper investigates how the electroweak vacuum angle at finite temperature could influence baryogenesis, suggesting a potential new source of CP-violation that might explain matter-antimatter asymmetry.

Contribution

It introduces a novel analysis of sphaleron-mediated CP-violation effects from the electroweak vacuum angle at finite temperature and derives a higher-order kinetic equation for baryon number.

Findings

CP-violation from the vacuum angle affects sphaleron processes.

Impact on existing baryogenesis models appears minor.

Vacuum angle alone could potentially enable baryogenesis.

Abstract

We initiate a study of cosmological implications of sphaleron-mediated CP-violation arising from the electroweak vacuum angle under the reasonable assumption that the semiclassical suppression is lifted at finite temperature. In this article, we explore the implications for existing scenarios of baryogenesis. Many compelling models of baryogenesis rely on electroweak sphalerons to relax a $(B+L)$ charge asymmetry. Depending on the sign of the CP-violating parameter, it is shown that the erasure of positive $(B+L)$ will proceed more or less quickly than the relaxation of negative $(B+L)$. This is a higher order effect in the kinetic equation for baryon number, which we derive here through order $n_{B+L}^2$. Its impact on known baryogenesis models therefore seems minor, since phenomenologically $n_{B+L}$ is much smaller than the entropy density. However, there remains an intriguing unexplored possibility that baryogenesis could be achieved with the vacuum angle alone providing the required CP-violation.