We consider a dark sector with SU(3)C×U(1)Y×U(1)X and three families of dark fermions that are chiral under dark U(1)X gauge symmetry, whereas scalar dark matter X is the SM singlet. U(1)X dark symmetry is spontaneously broken by nonzero VEV of dark Higgs field 〈Φ〉, generating the masses of dark fermions and dark photon Z′.
The resulting dark Higgs boson ϕ can be produced at the LHC by dark quark loop (involving 3 generation) and will decay into a pair of photon through charged dark fermion loop. Its decay width can be easily ∼45 GeV due to its possible decays into a pair of dark photon, which is not strongly constrained by the current LHC searches pp→ϕ→Z′Z′ followed by Z′ decays into the SM fermion pairs.
The scalar DM can achieve thermal relic density without conflict with direct detection bound or the invisible ϕ decay into a pair of DM.