Local Z2 scalar dark matter model confronting galactic GeV-scale γ-ray

Abstract

We present a scalar dark matter (DM) model where DM (XI) is stabilized by a local Z2 symmetry originating from a spontaneously broken local dark U(1)X. Compared with the usual scalar DM with a global Z2 symmetry, the local Z2 model possesses three new extra fields, dark photon Z′, dark Higgs ϕ and the excited partner of scalar DM (XR), with the kinetic mixing and Higgs portal interactions dictated by local dark gauge invariance. The resulting model can accommodate thermal relic density of scalar DM without conflict with the invisible Higgs branching ratio and the bounds from DM direct detections, thanks to the newly opened channels, XIXI→Z′Z′,ϕϕ. In particular, due to the new particles, the GeV scale γ-ray excess from the Galactic Center (GC) can be originated from the decay of dark Higgs boson which is produced in DM annihilations.