Electroweak Phase Transitions with BSM Fermions

TL;DR

This paper investigates how adding BSM fermions charged under SM gauge groups influences the electroweak phase transition in a 2HDM, showing a significant enhancement that aids in achieving a strong first order transition.

Contribution

It demonstrates that light BSM fermions can strengthen the electroweak phase transition in 2HDMs, providing a new approach to reconcile scalar mass constraints with phase transition requirements.

Findings

EWPT strength increased by about 40% with BSM fermions

Light fermions help reconcile scalar mass constraints with strong EWPT

Relevance for split supersymmetry scenarios

Abstract

We study the impact of additional beyond-the-Standard Model (BSM) fermions, charged under the Standard Model (SM) $SU(2)_L \otimes U(1)_Y$ gauge group, on the electroweak phase transition (EWPT) in a 2-Higgs-Doublet-Model (2HDM) of type II. We find that the strength of the EWPT can be enhanced by about 40% compared to the default 2HDM. Therefore, additional light fermions are a useful tool to weaken the tension between increasing mass constraints on BSM scalars and the requirement of additional light scalar degrees of freedom to accommodate a strong first order EWPT. The findings are of particular interest for a variety of (non-minimal) split supersymmetry scenarios which necessarily introduce additional light fermion degrees of freedom.