On the interpretation of a possible ∼ 750 GeV particle decaying into γγ

We consider interpretations of the recent ∼ 3σ reports by the cms and atlas collaborations of a possible x (∼750 gev) state decaying into γγ final states. we focus on the possibilities that this is a scalar or pseudoscalar electroweak isoscalar state produced by gluon-gluon fusion mediated by loops of heavy fermions. we consider several models for these fermions, including a single vector-like charge 2/3 t quark, a doublet of vector-like quarks (t, b), and a vector-like generation of quarks, with or without leptons that also contribute to the x → γγ decay amplitude. we also consider the possibility that x (750) is a dark matter mediator, with a neutral vector-like dark matter particle. these scenarios are compatible with the present and prospective direct limits on vector-like fermions from lhc runs 1 and 2, as well as indirect constraints from electroweak precision measurements, and we show that the required yukawa-like couplings between the x particle and the heavy vector-like fermions are small enough to be perturbative so long as the x particle has dominant decay modes into gg and γγ. the decays x → zz, zγ and w + w − are interesting prospective signatures that help distinguish between different vector-like fermion scenarios.