Strongly first-order electroweak phase transition by relatively heavy additional Higgs bosons

TL;DR

This paper explores how heavy additional Higgs bosons can induce a strong first-order electroweak phase transition, with implications for collider phenomenology and gravitational wave signals.

Contribution

It demonstrates that heavy scalar bosons near 1 TeV can still facilitate a first-order phase transition, providing new bounds and phenomenological insights.

Findings

Mass bounds on additional scalars are at the TeV scale.

Large deviations in triple Higgs coupling indicate phase transition.

Gravitational wave signals are weaker with heavier scalars.

Abstract

We discuss first-order electroweak phase transition in models with extended Higgs sectors for the case with relatively heavy additional scalar bosons. We first show that, by the combination of the sphaleron decoupling condition, perturbative unitarity and vacuum stability, mass upper bounds on additional scalar bosons can be obtained at the TeV scale even at the alignment limit where the lightest Higgs boson behaves exactly like the SM Higgs boson at tree level. We then discuss phenomenological impacts of the case with the additional scalar bosons with the mass near 1 TeV. Even when they are too heavy to be directly detected at current and future experiments at hadron colliders, the large deviation in the triple Higgs boson coupling can be a signature for first-order phase transition due to quantum effects of such heavy additional Higgs bosons. On the other hand, gravitational waves from the first-order phase transition are found to be weaker in this case as compared to that with lower masses of additional scalar bosons.