Dark sector shining through 750 GeV dark Higgs boson at the LHC

Abstract

We consider a dark sector with $SU(3)_C \times U(1)_Y \times U(1)_X$ 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 $\langle Φ\rangle$, generating the masses of dark fermions and dark photon $Z^\prime$. 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 $\sim 45$ GeV due to its possible decays into a pair of dark photon, which is not strongly constrained by the current LHC searches $pp \rightarrow ϕ\rightarrow Z^\prime Z^\prime$ followed by $Z^\prime$ 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.