Multi-Higgs doublet models with local $U(1)_H$ gauge symmetry and neutrino physics therein

Abstract

Multi-Higgs doublet models appear in many interesting extensions of the standard model (SM). But they suffer from Higgs-mediated flavor changing neutral current (FCNC) problem which is very generic. In this talk, I describe that this problem can be resolved or mitigated if we introduce local $U(1)_H$ Higgs flavor gauge symmetry. As examples, I describe chiral $U(1)_{H}$ models where the right-handed up-type quarks also carry $U(1)_H$ charges and discuss the top forward-backward asymmetry (FBA) and $B\rightarrow D^{(*)} \tau \nu$ puzzle. Next I describe the two-Higgs doublet models where the usual $Z_2$ symmetry is implemented to $U(1)_H$ and show how the Type-I and Type-II models are extended. One possible extension of Type-II has the same fermion contents with the leptophobic $E_6$ $Z^{'}$ model by Rosner, and I discuss the neutrino sector in this model briefly.