Strongly first-order electroweak phase transition and classical scale invariance

Abstract

In this work, we examine the possibility of realizing a strongly rst-order electroweak phase transi- tion within the minimal classically scale invariant extension of the standard model (SM), previously proposed and analyzed as a potential solution to the hierarchy problem. By introducing one com- plex gauge-singlet scalar and three (weak scale) right-handed Majorana neutrinos, the scenario was successfully capable of achieving a radiative breaking of the electroweak symmetry (by means of the Coleman-Weinberg Mechanism), inducing non-zero masses for the SM neutrinos (via the seesaw mechanism), presenting a pseudoscalar dark matter candidate (protected by the CP symmetry of the potential), and predicting the existence of a second CP-even boson (with suppressed couplings to the SM content) in addition to the 125 GeV scalar. In the present treatment, we construct the full nite-temperature one-loop eective potential of the model, including the resummed thermal daisy loops, and demonstrate that nite-temperature eects induce a rst-order electroweak phase transition. Requiring the thermally-driven rst-order phase transition to be suciently strong at the onset of the bubble nucleation (corresponding to nucleation temperatures TN 100-200 GeV) further constrains the model's parameter space; in particular, an O(0:01) fraction of the dark matter in the universe may be simultaneously accommodated with a strongly rst-order electroweak phase transition. Moreover, such a phase transition disfavors right-handed Majorana neutrino masses above several hundreds of GeV, connes the pseudoscalar dark matter masses to 1-2 TeV, pre- dicts the mass of the second CP-even scalar to be 100-300 GeV, and requires the mixing angle between the CP-even components of the SM doublet and the complex singlet to lie within the range 0:2 . sin ! . 0:4. The obtained results are displayed in comprehensive exclusion plots, identifying the viable regions of the parameter space. Many of these predictions lie within the reach of the next LHC run.