Enhanced $Z$ boson decays as a new probe of first-order electroweak phase transition at future lepton colliders

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.

8 pages, 6 figures; v2: some clarifications and references added, the version to appear in PRD

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Cited by in corpus (6)

• New Sensitivity Curves for Gravitational-Wave Signals from Cosmological Phase Transitions
• Phase transition dynamics and gravitational wave spectra of strong first-order phase transition in supercooled universe
• Bubble wall velocity during electroweak phase transition in the inert doublet model
• Sound velocity effects on the phase transition gravitational wave spectrum in the sound shell model
• Fundamental Physics and Cosmology with TianQin
• Complementary probe of dark matter blind spots by lepton colliders and gravitational waves