Abstract
We study phenomenological consequences of the strong first-order electroweak phase transition in an extension of the standard model with an inert doublet and vector-like leptons motivated by the muon $g-2$ anomaly and dark matter. We find that a condition for the strong first-order electroweak phase transition inevitably induces a large logarithmic enhancement in $Z$ boson decays, which relegates the explanation of the anomalous muon $g-2$ at below 2$\sigma$ level. Our analysis shows that future lepton collider experiments, especially the Giga-$Z$ at the International Linear Collider and Tera-$Z$ at the Circular Electron Positron Collider as well as Future Circular Collider have great capability to explore the nature of the electroweak phase transition, which is complementary to conventional approaches via measurements of the triple Higgs boson coupling and gravitational waves.
Highlights
From cosmological observations, the baryon asymmetry of the Universe (BAU) is found to be nB=nγ 1⁄4 ð6.09 Æ 0.06Þ × 10−10 [1], where nB denotes the baryon number density and nγ represents the photon number density
We show that the regions of the strong first-order electroweak phase transition (SFOEWPT) and dark matter (DM) in our scenario can be thoroughly probed by the future lepton collider experiments, especially the precise measurements
We have studied the possibility of a SFOEWPT and its phenomenological consequences in the VLIDM
Summary
The baryon asymmetry of the Universe (BAU) is found to be nB=nγ 1⁄4 ð6.09 Æ 0.06Þ × 10−10 [1], where nB denotes the baryon number density and nγ represents the photon number density. The scalar extensions of the SM are motivated by other fundamental problems, Such as dark matter (DM), inflation and neutrino masses and mixings, and some of the extended models could provide a solution of the muon magnetic dipole moment [ðg − 2Þμ] anomaly as well. Among such extensions, the SM augmented by an inert Higgs doublet [6], right-handed neutrinos and vectorlike leptons (denoted as VLIDM for short) has been studied from the viewpoints of DM and neutrino physics [7], or DM and the ðg − 2Þμ anomaly [8], or DM and inflation [9]. One-loop functions appearing in the Z boson decays are listed in the Appendix
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