Minimal Electroweak Baryogenesis via Domain Walls

TL;DR

This paper proposes a minimal electroweak baryogenesis mechanism involving domain walls in a singlet-extended Standard Model, which can be tested by various experimental searches due to its distinctive features.

Contribution

It introduces a novel EWBG mechanism via domain walls in a singlet scalar extension, highlighting conditions for domain wall dynamics and experimental testability.

Findings

Domain walls can generate baryon asymmetry during EW phase transition.

Parameter space includes singlet masses from sub-eV to 15 GeV with Higgs mixing.

The scenario is testable by fifth force, meson decay, and EDM experiments.

Abstract

The Standard Model extended by a real scalar singlet $S$ with an approximate $\mathbb{Z}_2$ symmetry offers a minimal framework for realizing electroweak baryogenesis (EWBG) during a first-order electroweak phase transition. In this work, we explore a novel mechanism where spontaneous $\mathbb{Z}_2$ breaking enables EWBG via domain walls separating two distinct phases of the $S$ field. These domain walls feature restored (or weakly broken) EW symmetry in their cores and sweep through space, generating the baryon asymmetry below the temperature of EW symmetry breaking. We identify the key conditions for the existence of EW-symmetric domain wall cores and analyze the dynamics required for wall propagation over sufficient spatial volumes. Additionally, we outline the CP-violating sources necessary for baryogenesis under different regimes of domain wall evolution. The parameter space accommodating this mechanism spans singlet masses from sub-eV to 15 GeV, accompanied by a non-vanishing mixing with the Higgs boson. Unlike the standard realization of EWBG in the minimal singlet-extended SM, which is notoriously difficult to test, our scenario can be probed by a wide range of existing and upcoming experiments, including fifth force searches, rare meson decays, and EDM measurements.