Discovering charged Higgs bosons in theWplus 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^'=Zd) with m_Zd<10 GeV, such a coupling leads to the dominant decay mode H^±→W^±+Zd (for m_H^±175 GeV), rather than the usual type I model decay H^±→τ^±ν, 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 (t̄) into H⁺b (H^-b̄) provides the dominant H^± production. Analysis of available LHC data can likely cover significant ranges of our parameters, if Zd→μ⁺μ^- has a branching ratio of ~20%. If the Zd 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_H^±175 GeV.