Nucleation is More than Critical -- A Case Study of the Electroweak Phase Transition in the NMSSM

TL;DR

This paper investigates the electroweak phase transition in the NMSSM, showing that nucleation probability analysis provides a more accurate picture of phase transition patterns than just examining critical temperatures, impacting baryogenesis viability.

Contribution

It demonstrates that nucleation probability calculations can differ from critical temperature analyses in identifying viable parameter space for electroweak baryogenesis in the NMSSM.

Findings

Nucleation analysis favors different parameter regions than critical temperature analysis.

Critical temperature analysis can be misleading for phase transition pattern assessment.

Nucleation probability is crucial for understanding the electroweak phase transition in the NMSSM.

Abstract

Electroweak baryogenesis is an attractive mechanism to generate the baryon asymmetry of the Universe via a strong first order electroweak phase transition. We compare the phase transition patterns suggested by the vacuum structure at the critical temperatures, at which local minima are degenerate, with those obtained from computing the probability for nucleation via tunneling through the barrier separating local minima. Heuristically, nucleation becomes difficult if the barrier between the local minima is too high, or if the distance (in field space) between the minima is too large. As an example of a model exhibiting such behavior, we study the Next-to-Minimal Supersymmetric Standard Model, whose scalar sector contains two SU(2) doublets and one gauge singlet. We find that the calculation of the nucleation probabilities prefers different regions of parameter space for a strong first order electroweak phase transition than the calculation based solely on the critical temperatures. Our results demonstrate that analyzing only the vacuum structure via the critical temperatures can provide a misleading picture of the phase transition patterns, and, in turn, of the parameter space suitable for electroweak baryogenesis.