First-order phase transitions in Twin Higgs models

Abstract: We revisit phase transitions in Twin Higgs (TH) models. We show that strong first-order phase transitions (FOPTs) can occur provided that appropriate source of $\mathbb{Z}_2$ symmetry breaking between the twin and Standard Model (SM) sectors is present. We found FOPTs in two classes of models. First: with hard $\mathbb{Z}_2$ breaking in the scalar potential allowing for FOPT. Second: with $\mathbb{Z}_2$ broken by enhanced Yukawa couplings of twin leptons. We also considered supersymmetric UV completion of the second scenario with light sleptons. The signal of gravitational waves produced during these phase transitions is typically small but can be close to the reach of AEDGE and Einstein Telescope in the case of the FOPT induced by light twin sleptons. Our results open a way to generate SM baryon asymmetry in TH models.