Electroweak phase transition triggered by fermion sector

TL;DR

This paper explores how adding specific fermions to the Standard Model can induce a strong first-order electroweak phase transition by creating a potential barrier without relying on scalar fields.

Contribution

It demonstrates that fermion sector extensions with particular mass hierarchies and mixing can generate the necessary barrier for a first-order phase transition, a novel approach compared to scalar-driven models.

Findings

Fermion extensions can produce potential barriers for phase transition.

Two patterns of potential barriers are identified involving fermion-induced terms.

Fermion sector modifications can achieve strongly first-order electroweak phase transition.

Abstract

To realize first-order electroweak phase transition, it is necessary to generate a barrier in the thermal Higgs potential, which is usually triggered by scalar degree of freedom. We instead investigate phase transition patterns in pure fermion extensions of the standard model, and find that additional fermions with mass hierarchy and mixing could develop such barrier and realize strongly first-order phase transition in such models. In the Higgs potential with polynomial parametrization, the barrier can be generated in the following two patterns: (I) positive quadratic term, negative cubic term and positive quartic term or (II) positive quadratic term, negative quartic term and positive higher dimensional term, such as dimensional 6 operator.