The complex scalar dark matter (DM) candidate in the gauged two-Higgs-doublet model, stabilized by a peculiar hidden parity (h parity), is studied in detail. We explore the parameter space for the DM candidate by taking into account the most recent DM constraints from various experiments, in particular, the PLANCK relic density measurement and the current DM direct detection limit from XENON1T. We separate our analysis in three possible compositions for the mixing of the complex scalar. We first constrain our parameter space with the vacuum stability and perturbative unitarity conditions for the scalar potential, LHC Higgs measurements, plus Drell-Yan and electroweak precision test constraints on the gauge sector. We find that DM dominated by composition of the inert doublet scalar is completely excluded by further combining the previous constraints with both the latest results from PLANCK and XENON1T. We also demonstrate that the remaining parameter space with two other DM compositions can be further tested by indirect detection like the future Cherenkov Telescope Array gamma-ray telescope.

Pair production of Higgs bosons at the Large Hadron Collider (LHC) is known to be important for the determination of the Higgs boson self-coupling and as a probe of new physics beyond the Standard Model (SM), especially the existence of new fundamental scalar bosons. In this paper we study in detail the pair production of Higgs bosons at the LHC in a well-motivated model-the gauged two-Higgs-doublet model-in which the two Higgs doublets are properly embedded into a gauged SUð2Þ H and a dark matter candidate emerges naturally due to the gauge symmetry. Besides the deviations of the Higgs couplings from the SM predictions, the existence of new scalars could significantly enhance the production cross section of Higgs boson pairs at the LHC. However, when we take into account the relic density of dark matter and the null results of direct detection experiments, only a moderate enhancement can be obtained. We also comment on the capability of the LHC to distinguish the Higgs pair signal due to a generic 400 GeV scalar resonance in the γγbb final state from the SM prediction, assuming that their Higgs pair production cross sections are the same.

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