Symmetries of Hot SM, Magnetic Flux & Baryogenesis from Helicity Decay

TL;DR

This paper explores the electroweak crossover in the early Universe, focusing on symmetries, magnetic flux, and baryogenesis, revealing new effects and uncertainties in baryon asymmetry estimates from magnetic helicity decay.

Contribution

It introduces a gauge-invariant mixing angle, analyzes symmetry breaking patterns, and identifies a previously overlooked non-perturbative process affecting baryogenesis from magnetic helicity decay.

Findings

Baryon asymmetry is affected by a factor of order one due to the mixing angle definition.

Approximate conservation of magnetic flux influences baryogenesis calculations.

A new non-perturbative process impacts magnetic helicity decay and baryon asymmetry estimates.

Abstract

We revisit the electroweak crossover of the Standard Model (SM) in the early Universe, focusing on the interplay between generalized global symmetries, magnetic flux dynamics, and baryogenesis. Employing the dimensionally reduced 3d effective field theory of the SM at high temperature, we identify the symmetry structure -- including higher-form and magnetic symmetries -- and analyze their spontaneous breaking patterns across the crossover. We further define a gauge-invariant mixing angle that interpolates between $\mathrm{U}(1)_Y$ and $\mathrm{U}(1)_\mathrm{em}$ magnetic fields. Based on this framework, we examine baryogenesis via decaying magnetic helicity and identify three key effects: the baryon asymmetry is modified by an $\mathcal{O}(1)$ factor due to (1) the gauge-invariant definition of the mixing angle and (2) the approximate conservation of the unconfined magnetic flux; (3) a novel non-perturbative process in the presence of magnetic flux, which has been overlooked in previous analyses. Our findings suggest that the previous estimation of baryon asymmetry from the magnetic helicity decay may have sizable uncertainties, and we caution against relying on it, calling for further investigation.