Spontaneous CP violation electroweak baryogenesis and gravitational wave through multi-step phase transitions

TL;DR

This paper explores how multi-step phase transitions in an extended two-Higgs-doublet model can facilitate spontaneous CP violation electroweak baryogenesis and produce detectable gravitational waves.

Contribution

It introduces a novel multi-step phase transition framework for electroweak baryogenesis with spontaneous CP violation in a singlet pseudoscalar extended model.

Findings

Two-step phase transitions can generate baryon asymmetry during the first step.

Gravitational wave spectra from these transitions may have one or two peaks.

Future detectors could potentially observe these gravitational wave signals.

Abstract

In a singlet pseudoscalar extension of the two-Higgs-doublet model we discuss spontaneous CP violation electroweak baryogenesis via two different patterns of phase transitions (PTs): (i) two-step PTs whose first-step and second-step are strongly first-order; (ii) three-step PTs whose first-step is second-order and the second-step and third-step are strongly first-order. For the case of the two-step pattern, the first-step PT takes place at a high temperature, converting the origin phase into an electroweak symmetry broken phase and breaking the CP symmetry spontaneously. Thus, the baryon number is produced during the first-step PT. At the second-step PT, the phase is converted into the observed vacuum at zero temperature, and the CP-symmetry is restored. In both phases the sphaleron processes are sufficiently suppressed, which keep the baryon number unchanged. For the case of the three-step PTs, the pseudoscalar field firstly acquires a nonzero VEV, and VEVs of other fields still remain zero during the first-step PT. The following PTs and electroweak baryogenesis are similar to the case of the two-step PTs. In addition, the gravitational wave spectra can have one or two peaks through the two-step and the three-step PTs, and we discuss the detectability at the future gravitational wave detectors.