Dark Matter and Dark Force in the Type-I Inert 2HDM with Local U(1)_H Gauge Symmetry

TL;DR

This paper explores a dark matter model within a two-Higgs-doublet framework featuring a local U(1)_H gauge symmetry, revealing new viable dark matter scenarios and distinctive experimental signatures.

Contribution

It introduces a novel inert 2HDM with local U(1)_H symmetry, enabling a ~10 GeV dark matter candidate and unique decay channels not present in traditional models.

Findings

U(1)_H gauge interaction constrains the model parameters.

The model revives the ~10 GeV dark matter scenario.

Exotic Higgs decays like h -> Z_H Z_H are predicted.

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 (Z_H) 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 Z_2 symmetry, is revived in our model because of newly open channels, H H -> Z_H Z_H , Z_H Z. Exotic Higgs decays, h -> Z_H Z_H, Z Z_H, would be distinctive signatures of the inert 2HDM with local U(1)_H symmetry.