  We study Higgs and dark matter physics in the type-II two-Higgs-doublet model
(2HDM) with an extra U(1)_H gauge symmetry, inspired by the E_6 grand unified
theory (GUT). From the viewpoint of the bottom-up approach, the additional
U(1)_H gauge symmetry plays a crucial role in avoiding the tree-level flavor
changing neutral currents mediated by neutral Higgs bosons in general 2HDMs. In
the model with U(1)_H gauge symmetry, which has Type-II Yukawa couplings, we
have to introduce additional chiral fermions that are charged under the U(1)_H
gauge symmetry as well as under the Standard-Model (SM) gauge symmetry in order
to cancel chiral gauge anomalies. For the U(1)_H charge assignment and the
extra matters, we adopt the ones inspired by the E_6 GUT: the extra quark-like
and lepton-like fermions with the non-trivial U(1)_H charges. We discuss their
contributions to the physical observables, such as the measurements of Higgs
physics and electro-weak interactions, and investigate the consistency with the
experimental results. Furthermore, we could find extra neutral particles like
the SM neutrinos after the electro-weak symmetry breaking, and they could be
stable, because of the remnant symmetry after U(1)_H symmetry breaking. We also
discuss the thermal relic density and the (in)direct-detections of this dark
matter candidate.
