First-order electroweak phase transition in a complex singlet model with $\mathbb{Z}_3$ symmetry

Understand

We consider an extension of the Standard Model with a complex singlet scalar, where a global $U(1)$ symmetry is explicitly broken to $\mathbb{Z}_3$ symmetry.

• We study the two-step electroweak phase transition in the model and find that it can be of first-order if the heavy scalar mass falls in the range of $1-2$~TeV and the mixing angle $\left | \theta \right |\gtrsim 0.2$ ($11.5^{\circ}$).
• The Higgs signal strength measurements at the LHC, on the other hand, restrict the mixing angle $\left | \theta \right |\lesssim 0.4$ ($23^{\circ}$).
• Future colliders including high-luminosity LHC can probe the remaining parameter space of first-order phase transition in this scenario.