Diphoton and Dark Matter from Cascade Decay

We propose a simplified model to study the possible new heavy diphoton resonance from cascade decay of a heavier particle at colliders, which may be related to the dark matter or other new physics beyond the standard model. Model-independent constraints and predictions on the allowed couplings for generating the observed diphoton data are studied in detail. We demonstrate that this scenario can be tested by the possible four-photon signal or the $WW\mathrm{/}ZZ\mathrm{/}Z\gamma$ resonances. Meanwhile, this cascade decay scenario also provides us with the dark matter candidates, which is consistent with the observed dark matter relic density.