The diphoton resonance as a gravity mediator of dark matter

TL;DR

This paper explores interpreting the 750 GeV diphoton excess as a spin-two graviton mediator connecting dark matter and the Standard Model, analyzing its couplings, relic density, and experimental constraints.

Contribution

It models non-universal couplings of a KK graviton to gauge bosons and dark matter, and assesses its viability as an explanation for the diphoton excess and dark matter relic density.

Findings

Scalar, fermion, or vector dark matter can account for relic density.

Invisible decay of the resonance into dark matter is subdominant.

The model is compatible with existing collider constraints.

Abstract

We consider the possibility of interpreting the recently reported diphoton excess at 750 GeV as a spin-two massive particle (such as a Kaluza-Klein graviton in warped extra-dimensions) which serves as a mediator to Dark Matter via its gravitational couplings to the dark sector and to the Standard Model (SM). We model non-universal couplings of the resonance to gauge bosons in the SM and to Dark Matter as a function on their localization in the extra dimension. We find that scalar, fermion or vector dark matter can saturate the dark matter relic density by the annihilation of dark matter into a pair of the SM particles or heavy resonances, in agreement with the diphoton resonance signal strength. We check the compatibility of our hypothesis with other searches for the KK graviton. We show that the invisible decay rate of the resonance into a pair of dark matter is subdominant in the region of the correct relic density, hence leading to no constraints from the mono-jet bound at 8 TeV via the gluon coupling. We also discuss the kinematic features of the decay products of a KK graviton to distinguish the KK graviton from the SM backgrounds or a scalar particle interpretation of the diphoton resonance.