Baryon asymmetry from electroweak tachyonic preheating

TL;DR

This work shows that a cold, tachyonic electroweak transition within the (Extended) Standard Model can generate the observed baryon asymmetry if a modest CP-violating coupling is present. Using lattice simulations of the SU(2)-Higgs model with an effective CP term, the authors track Chern-Simons number generation during tachyonic preheating and connect it to n_B/n_γ through the electroweak anomaly. They provide analytic and numerical insights into the initial CP-driven rise, the role of the Higgs-to-W mass ratio, and the post-transition sphaleron dynamics, ultimately constraining the CP-violation strength needed to match observations. The results suggest that SM CP violation, enhanced by non-equilibrium tachyonic dynamics, could be sufficient for baryogenesis, motivating further exploration of low-scale, tachyonic scenarios.

Abstract

We consider a scenario in which the baryon asymmetry was created in the early universe during a cold electroweak transition. The spinodal instability of the Higgs field caused by a rapid change of sign of its effective mass-squared parameter induces tachyonic preheating. We study the development of Chern-Simons number in this transition by numerical lattice simulations of the SU(2)-Higgs model with an added effective CP-violating term. A net asymmetry is produced, and we study its dependence on the size of CP violation and the ratio of Higgs to W mass.