750 GeV diphoton excess and a dark matter messenger at the Galactic Center

The first data from the LHC run 2 have shown a possible excess in diphoton events with invariant mass $\ensuremath{\sim}750\text{ }\text{ }\mathrm{GeV}$, suggesting the existence of a new resonance which may decay dominantly into dark matter (DM) particles. We show in a simple model that the reported diphoton excess at the LHC is consistent with another photon excess, the 2 GeV excess in cosmic gamma-ray fluxes towards the Galactic Center observed by the Fermi-LAT. Both the excesses can be simultaneously explained by a $\ensuremath{\sim}60\text{ }\text{ }\mathrm{GeV}$ scalar DM particle annihilating dominantly into two gluons with a typical thermal annihilation cross section, which leads to the prediction of a width-to-mass ratio $\mathrm{\ensuremath{\Gamma}}/M\ensuremath{\approx}\mathcal{O}({10}^{\ensuremath{-}2})$ of the resonance. The upper limit on the dijet search at LHC run 1 leads to a lower limit on the predicted cross section for DM annihilating into $\ensuremath{\gamma}\ensuremath{\gamma}$ final states $⟨\ensuremath{\sigma}v{⟩}_{\ensuremath{\gamma}\ensuremath{\gamma}}\ensuremath{\gtrsim}\mathcal{O}({10}^{\ensuremath{-}30})\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. Both the predictions can be tested by the LHC, Fermi-LAT, and future experiments.