# Dynamics of Electroweak Phase Transition In Singlet-Scalar Extension of the Standard Model

## TL;DR

This paper investigates the electroweak phase transition in a singlet-scalar extension of the Standard Model, revealing that bubble nucleation constraints significantly limit the parameter space for successful electroweak baryogenesis.

## Contribution

It provides a detailed analysis of bubble nucleation temperatures and dynamics, identifying key constraints that restrict viable models for electroweak baryogenesis.

## Key findings

- Many parameter regions do not allow bubble nucleation at finite temperature.
- Two-step phase transition regions are largely excluded by nucleation constraints.
- Expanding bubble walls must remain subluminal to generate baryon asymmetry.

## Abstract

An addition to the Standard Model of a real, gauge-singlet scalar field, coupled via a Higgs portal interaction, can reopen the possibility of a strongly first-order electroweak phase transition (EWPT) and successful electroweak baryogenesis (EWBG). If a discrete symmetry that forbids doublet-singlet mixing is present, this model is notoriously difficult to test at the Large Hadron Collider. As a result, it emerged as a useful benchmark for evaluating the capabilities of proposed future colliders to conclusively test EWPT and EWBG. In this paper, we evaluate the bubble nucleation temperature throughout the parameter space of this model where a first-order transition is expected. We find that in large parts of this parameter space, bubbles in fact do not nucleate at any finite temperature, eliminating these models as viable EWBG scenarios. This constraint eliminates most of the region where a "two-step" phase transition is naively predicted, while the "one-step" transition region is largely unaffected. In addition, expanding bubble walls must not reach relativistic speeds during the transition for baryon asymmetry to be generated. We show that this condition further reduces the parameter space with viable EWBG.