Nonperturbative study of the electroweak phase transition in the real scalar singlet extended standard model

We perform a nonperturbative lattice study of the electroweak phase transition in the real singlet scalar extension of the Standard Model. We consider both the heavy and light singletlike scalar regimes at nonzero singlet-doublet mixing angle. After reviewing features of the lattice method relevant for phase transition studies, we analyze the dependence of phase transition thermodynamics on phenomenologically relevant parameters. In the heavy singletlike scalar regime, we find that the transition is a crossover for small doublet-singlet mixing angles, despite the presence of an energy barrier in the tree-level potential. The transition becomes first order for sufficiently large mixing angles. We find two-loop perturbation theory to agree closely with the lattice results for all thermodynamical quantities considered here (critical temperature, order parameter discontinuity, latent heat) when the transition is strongly first order. For the light singletlike scalar regime relevant to exotic Higgs decays, we update previous one-loop perturbative results using the two-loop loop dimensionally reduced effective field theory and assess the nature of the transition with lattice simulations at set of benchmark parameter points. For fixed singletlike scalar mass the transition becomes crossover when the magnitude of the Higgs-singlet portal coupling is small. We perform our simulations in the high-temperature effective theory, which we briefly review, and present analytic expressions for the relevant lattice-continuum relations. Published by the American Physical Society 2024