Vacuum structure and electroweak phase transition in singlet scalar dark matter

TL;DR

This paper analytically studies the electroweak phase transition in a singlet scalar dark matter model, identifying conditions for first- and second-order transitions and comparing them with dark matter and collider constraints.

Contribution

It provides a comprehensive analysis of all possible electroweak phase transition scenarios in the model, highlighting the unique two-step first-order transition and its experimental implications.

Findings

Only the two-step transition can be first-order.

Second-order one-step transition can evade dark matter constraints.

Two-step first-order transition is testable at future colliders.

Abstract

In the presence of a real singlet scalar field with $\mathbb{Z}_2$ symmetry in addition to the Higgs field in the Standard Model, we analytically investigate all possible one-step and two-step electroweak phase transitions (EWPT) in the high-temperature expansion limit. In particular, we examine the possibility of a first-order phase transition in an intermediate temperature interval of the universe for two-step scenarios. In all scenarios, we provide with necessary conditions on the parameters of the model to address a first- or second-order phase transition if ever possible in the high-temperature approximation. We show that among all possible EWPT channels in this model, only the two-step phase transition $(0,0)\to(0,w)\to (v,0)$ can be of first-order type, either in the first or second step. The conditions obtained for EWPT is confronted with the dark matter (DM) and collider constraints. It is shown that the second-order one-step $(0,0)\to(v,0)$ scenario can evade the DM constraints, but it is not accessible to future colliders. The two-step first-order EWPT scenario $(0,0)\to(0,w)\to (v,0)$, except for small DM masses, is excluded by direct detection experiments XENON1T/LUX, but it is accessible in future colliders ILC/TLEP.