ALP-Assisted Strong First-Order Electroweak Phase Transition and Baryogenesis

TL;DR

This paper explores how axion-like particles (ALPs) can induce a strong first-order electroweak phase transition, potentially explaining baryogenesis while remaining consistent with current experimental bounds.

Contribution

It introduces a detailed analysis of ALP-induced electroweak phase transition dynamics and identifies viable parameter space for baryogenesis without conflicting with existing constraints.

Findings

ALPs can have masses from MeV to GeV scale.

Baryon asymmetry can be generated without violating electric dipole moment bounds.

Future experiments can probe the viable parameter space.

Abstract

Axion-like particles (ALPs) can be naturally lighter than the electroweak scale. We consider an ALP that couples to the Standard Model Higgs to achieve the strong first-order electroweak phase transition. We discuss the two-field dynamics of the phase transition and the associated computation in detail and identify the viable parameter space. The ALP mass can be from the MeV to GeV scale. Baryon asymmetry can be explained by local baryogenesis without violating the current electron and atom electric dipole moment bound in most of the viable parameter space. The viable parameter space can be probed through Higgs exotic decay, rare kaon decay, the electron and atomic electric dipole moment, and the effective number of neutrinos in the cosmic microwave background in the future. The gravitational-wave signal is too weak to be detected.