First Order Electroweak Phase Transition from (Non)Conformal Extensions of the Standard Model

TL;DR

This paper investigates how certain extensions of the Standard Model can produce a first order electroweak phase transition, with implications for dark matter and testability at the LHC, focusing on conformal and non-conformal scenarios.

Contribution

It compares conformal and non-conformal extensions of the Standard Model in generating a first order electroweak phase transition and explores their dark matter implications.

Findings

First order phase transition achievable in specific parameter regions.

Models with light new particles are testable at LHC Run 2.

Additional degrees of freedom are needed for dark matter and phase transition compatibility.

Abstract

We analyse and compare the finite-temperature electroweak phase transition properties of classically (non)conformal extensions of the Standard Model. In the classically conformal scenarios the breaking of the electroweak symmetry is generated radiatively. The models feature new scalars coupled conformally to the Higgs sector as well as new fermions. We uncover the parameter space leading to a first order phase transition with(out) the Veltman conditions. We also discuss dark (matter) aspects of some of the models and compare with existing literature when appropriate. We observe that to accommodate both, a first order electroweak phase transition, and a phenomenologically viable dark matter candidate requires to go beyond the simplest extensions of the Standard Model. Furthermore these extensions must all feature new degrees of freedom that are naturally lighter than a TeV and therefore the associated models are testable at the upcoming Large Hadron Collider run two experiments.