Dark Matter and Dark Force in the Type-I Inert 2HDM with Local U(1)H Gauge Symmetry
Abstract
We discuss dark matter (DM) physics in the Type-I inert two-Higgs-doublet model (2HDM) with local U(1)H Higgs gauge symmetry. The local U(1)H gauge symmetry is assigned to the extra Higgs doublet in order to avoid the Higgs-mediated flavor problems, and it spontaneously breaks down to its discrete subgroup. The lightest neutral scalar component H of the U(1)H-charged Higgs doublet, which does not have Yukawa couplings with the Standard-Model (SM) fermions, is stable because of the remnant discrete symmetry, and it interacts with the SM particles through the U(1)H gauge boson (ZH) exchange as well as the SM boson exchange. We first investigate the constraint on the U(1)H gauge interaction, especially through the kinetic and mass mixing between the SM gauge bosons and the extra gauge boson. Then we discuss dark matter physics in our 2HDM: thermal relic density, and direct/indirect detections of dark matter. The additional U(1)H gauge interaction plays a crucial role in reducing the DM thermal relic density. The most important result within the inert DM model with local U(1)H symmetry is that ~ O(10) GeV dark matter scenario, which is strongly disfavored in the usual Inert Doublet Model (IDM) with Z2 symmetry, is revived in our model because of newly open channels, H H -> ZH ZH , ZH Z. Exotic Higgs decays, h -> ZH ZH, Z ZH, would be distinctive signatures of the inert 2HDM with local U(1)H symmetry.
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