Electroweak Phase Transition in Scale Invariant Standard Model

TL;DR

This paper explores a minimal scale-invariant extension of the Standard Model with two singlet scalars, demonstrating a strong first-order electroweak phase transition suitable for baryogenesis, while also accounting for dark matter constraints.

Contribution

It introduces a minimal two-scalar extension that achieves a strong electroweak phase transition and explains dark matter relic density within experimental bounds.

Findings

Electroweak phase transition is strongly first-order.

Dark matter relic density matches observed value.

Dark matter candidate mass is constrained to be above 4.5 TeV.

Abstract

In an extension to the scale invariant standard model by two real singlet scalars $s$ and $s'$ in addition to the Higgs field, we investigate the strong first-order electroweak phase transition as a requirement for baryogenesis. This is the minimal extension to the scale invariant standard model with two extra degrees of freedom that possesses the physical Higgs mass of $125$ GeV. The scalar $s'$ being stable because of the $\mathbb Z_2$ discrete symmetry is taken as the dark matter candidate. We then show that the electroweak phase transition is strongly first-order, the dark matter relic density takes the desired value $\Omega_{\text{DM}}h^2 \sim 0.11$, and the constraints from direct detection experiments are respected only if $m_{s'}\equiv m_{\text{DM}} \gtrsim 4.5$ TeV. The model also puts a lower bound on the scalon mass, $m_s \gtrsim 200$ GeV.