[PhD Thesis Presentation] -Daisuke Takahashi- Minimal Gauged U(1) Extension of the Standard Model with Classical Scale Invariance and Phenomenology

Speaker: Daisuke Takahashi

Titile: Minimal Gauged U(1) Extension of the Standard Model with Classical Scale Invariance and Phenomenology

Although the Standard Model (SM) is the best theory in describing phenomena among elementary particles, it suffers from several problems, such as the gauge hierarchy problem, origin of the electroweak symmetry breaking, non-zero neutrino mass, and no candidate of dark matter. For solving these problems, we consider minimal U(1) extension of the SM with the classically conformal invariance, where an anomaly-free U(1) gauge symmetry is introduced along with a U(1) Higgs field and three right-handed neutrinos (RHNs) for the seesaw mechanism generating neutrino masses. With no mass term allowed by the classically conformal invariance, the U(1) gauge symmetry is broken through the Coleman-Weinberg mechanism, which subsequently triggers the electroweak symmetry breaking. We perform parameter scan and identify regions resolving the SM Higgs vacuum instability, while satisfying the LHC Run-2 bound on the U(1) gauge boson production and the naturalness constraint. We also investigate cosmological aspects of the model. Introducing Z2 parity, one RHN being an unique parity-odd particle in the model serves as dark matter. A successful inflation scenario is possible by identifying the U(1) Higgs boson with inflaton and introducing its non-minimal gravitational coupling. Interestingly, the LHC physics and cosmological observations are complementary narrowing down the model parameter space.