Phenomenological study of a gauged Lμ-Lτ model with a scalar leptoquark

A Z′ gauge boson with sub-GeV mass has acquired a significant interest in phenomenology, particularly in view of the muon g-2 anomaly and coherent elastic neutrino-nucleon scattering. The latter is challenged by the nuclear recoil energy of a few tens of keV but has been observed by the COHERENT experiment. To further reconcile the observed excesses in R(D(∗)) from semileptonic charmful B decays and in the W boson mass, we investigate a model with a gauged U(1)Lμ-Lτ symmetry and a scalar leptoquark. In contrast to the mechanism that involves kinetic mixing between the gauge bosons of U(1)em and U(1)Lμ-Lτ, we adopt a dynamical symmetry breaking of U(1)Lμ-Lτ by incorporating an additional Higgs doublet. Through mixing with the U(1)Lμ-Lτ-charged Higgs doublet, new Higgs decay channels h→Z1Z1/Z1Z2 occur at percent-level branching ratios, which could be accessible at the LHC. The W-mass anomaly observed by CDF II can be potentially resolved through the enhancement in the oblique parameter T. Due to the flavored gauge symmetry, the introduced scalar leptoquark S13=(3¯,1,2/3) exhibits a unique coupling to the τ lepton, offering an explanation for the excesses observed in R(D(∗)). Moreover, τ→μ(Z1→)e-e+ via the resonant light gauge boson decay can reach the sensitivity of Belle II at an integrated luminosity of 50 ab-1.