Strong phase transition, dark matter and vacuum stability from simple hidden sectors

TL;DR

This paper explores simple hidden sector extensions of the Standard Model with scalar or fermionic singlets, demonstrating their potential to explain dark matter, enable strong electroweak phase transitions, and maintain vacuum stability up to high scales.

Contribution

It introduces and analyzes minimal portal models with singlet scalars or fermions, showing their capability to produce dark matter and facilitate electroweak baryogenesis while remaining stable and perturbative.

Findings

Dark matter can be produced via freeze-in or freeze-out.

Only the fermionic model allows a strong electroweak phase transition.

Scalar sector remains stable and perturbative up to high scales.

Abstract

Motivated by the possibility to explain dark matter abundance and strong electroweak phase transition, we consider simple extensions of the Standard Model containing singlet fields coupled with the Standard Model via a scalar portal. Concretely, we consider a basic portal model consisting of a singlet scalar with $Z_2$ symmetry and a model containing a singlet fermion connected with the Standard Model fields via a singlet scalar portal. We perform a Monte Carlo analysis of the parameter space of each model, and we find that in both cases the dark matter abundance can be produced either via freeze-out or freeze-in mechanisms, but only in the latter model one can obtain also a strong electroweak phase transition required by the successful electroweak baryogenesis. We impose the direct search limits and consider systematically the possibility that the model produces only a subdominant portion of the dark matter abundance. We also study the renormalization group evolution of the couplings of the model to determine if the scalar sector of the model remains stable and perturbative up to high scales. With explicit examples of benchmark values of the couplings at weak scale, we show that this is possible. Models of this type are further motivated by the possibility that the excursions of the Higgs field at the end of inflation are large and could directly probe the instability region of the Standard Model.