Singlet Higgs Phenomenology and the Electroweak Phase Transition

TL;DR

This work assesses whether a minimal SM extension with a real gauge singlet can support electroweak baryogenesis by producing a strong first-order electroweak phase transition. Using a finite-temperature effective potential, it derives a compact criterion for a strong transition and identifies five routes—primarily tree-level singlet interactions and pre-existing high-T minima—that enhance $\varphi_c/T_c$; it maps the viable parameter space under LEP and electroweak precision constraints. The zero-temperature phenomenology is then tied to collider observables: Higgs mixing alters production and decays, enabling exotic signatures such as $h_1\to h_2h_2$ and, in $Z_2$-symmetric cases, potential dark matter candidates. The results show that many EWPT-viable singlet scenarios are testable at the LHC and a future Linear Collider via Higgs measurements and possible exotic final states, providing a concrete path to probe EWPT dynamics in extended scalar sectors.

Abstract

We study the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. We determine the conditions on the scalar potential parameters that lead to a strong first order phase transition as needed to produce the observed baryon asymmetry of the universe. We analyze the constraints on the potential parameters derived from Higgs boson searches at LEP and electroweak precision observables. For models that satisfy these constraints and that produce a strong first order phase transition, we discuss the prospective signatures in future Higgs studies at the Large Hadron Collider and a Linear Collider. We argue that such studies will provide powerful probes of phase transition dynamics in models with an extended scalar sector.