Discovering charged Higgs bosons in the W plus dark vector boson decay mode

In two-Higgs doublet extensions of the Standard Model, flavor-changing neutral current constraints can be addressed by introducing a U(1)' gauge symmetry, under which the Higgs doublets carry different charges. That scenario implies the presence of a H(+/-)W(-/+)Z' vertex at tree level. For the light dark Z model (Z' = Z(d)) with m(Zd) < 10 GeV, such a coupling leads to the dominant decay mode H-+/- -> W-+/- + Z(d) (for m(II +/-) less than or similar to 175 GeV), rather than the usual type I model decay H-+/- -> tau(+/-)upsilon, for a broad range of parameters. We find that current analyses do not place significant bounds on this scenario. Over much of the parameter space considered, the decay of a pair-produced t((t)over bar) into H+ b (H-(b)over bar) provides the dominant H-+/- production. Analysis of available LHC data can likely cover significant ranges of our parameters, if Z(d) -> mu(+) mu(-) has a branching ratio of similar to 20%. If the Z(d) decays mainly invisibly then probing the entire relevant parameter space would likely require additional data from future LHC runs. We briefly discuss the phenomenology for m(II +/-) greater than or similar to 175 GeV.