Abstract
The nature of electroweak (EW) phase transition (PT) is of great importance. It may give a clue to the origin of baryon asymmetry if EWPT is strong first order. Although it is a cross over within the standard model (SM), a great many extensions of the SM are capable of altering the nature. Thus, gravitational wave (GW), which is supposed to be relics of strong first order PT, is a good complementary probe to new physics beyond SM (BSM). We in this paper elaborate the patterns of strong first order EWPT in the next to simplest extension to the SM Higgs sector, by introducing a Z3-symmetric singlet scalar. We find that, in the Z3-symmetric limit, the tree level barrier could lead to strong first order EWPT either via three or two-step PT. Moreover, they could produce two sources of GW, despite of the undetectability from the first-step strong first order PT for the near future GW experiments. But the other source with significant supercooling which then gives rise to alpha sim mathcal{O}(0.1) almost can be wholly covered by future space-based GW interferometers such as eLISA, DECIGO and BBO.
Highlights
Between the EW vacuum and a metastable vacuum at tree or loop level [3, 4]
As a matter of fact, SFOEWPT can be probed via the Higgs selfcoupling measurement [12, 23, 24, 40–52], a sufficiently good precision is unlikely until the generation of colliders such as the International Linear Collider (ILC) [53–58] and the Compact Linear Collider (CLIC) [59, 60]
After employing analytical and numerical methods, we find that the model shows remarkable new features such as the three-step phase transition (PT), realizing SFOEWPT with strong gravitational wave (GW) signals which can be well received by eLISA and DECIGO
Summary
Despite of receiving much more attention, a Z2 discrete symmetry does not take obvious advantage over Z3 from theoretical viewpoints. One can consider two loop radiative neutrino mass models with DM running in the loop [78, 83, 88], where DM candidate is well furnished, for instance, a Dirac fermion or even another singlet scalar lighter than S. Since this DM phenomenology involves other parameters and can be irrelevant to PT, we will not enter its details in this paper, keeping in mind that the Z3-symmetric extension could be a good simplified model for many BSM for DM and neutrino physics. Program CosmoTransitions [89], which we adopt to study the phase transitions in the model described .
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