The LHC diphoton resonance and dark matter

A resonance with a mass of approximately 750 GeV has recently been “observed” at the LHC in its diphoton decay. If this state is not simply a statistical fluctuation which will disappear with more data, it could have important implications not only for particle physics but also for cosmology. In this note, we analyze the implications of such a resonance for the dark matter (DM). Assuming a spin-12 DM particle, we first verify that indeed the correct relic density can be obtained for a wide range of the particle mass and weak scale coupling, that are compatible with present data. We then show that the combination of near future direct and indirect detection experiments will allow to probe the CP-nature of the mediator resonance, i.e. discriminate whether it is a scalar or a pseudoscalar like particle.