Vector Dark Matter in a $U(1)_X$ extended 2HDM

Abstract: We investigate the possibility of having a vector boson dark matter in a $U(1)_X$ extended two-Higgs-doublet model (2HDM) setup. The gauge boson gains mass when a SM singlet complex scalar, which is charged under the dark $U(1)_X$ symmetry, acquires vacuum expectation value (\textit{vev}). This scalar acts as the connection between the SM sector and DM via the Higgs portal. An additional exact charge conjugation symmetry inhibits the mixing of this gauge boson with the photon, thereby confirming the stability of DM. On the other hand, 2HDM with Type I $Z_2$ restriction can offer a non-standard Higgs in the lighter mass range. This freedom allows us to accommodate dark matter mass in the (40-60) GeV regime where the direct detection constraints are strongest. We study the dark matter phenomenology of such a model while taking care of all possible theoretical and experimental constraints.