Diphoton resonance confronts dark matter

TL;DR

This paper proposes a model linking a 750 GeV diphoton excess to dark matter, exploring how scalar mediators and effective couplings can explain experimental signals while satisfying relic density and detection constraints.

Contribution

It introduces a simple extension of the Standard Model with a Dirac fermion dark matter and a singlet scalar, explaining the diphoton excess via scalar decays and analyzing experimental constraints.

Findings

Mono-jet and gamma-ray observations constrain the model parameters.

Cascade decay scenarios allow smaller effective couplings for scalars.

Future LHC and gamma-ray searches can test the model.

Abstract

As an interpretation of the 750 GeV diphoton excesses recently reported by both ATLAS and CMS collaborations, we consider a simple extension of the Standard Model with a Dirac fermion dark matter where a singlet complex scalar field mediates between dark matter and SM particles via effective couplings to SM gauge bosons and/or Higgs-portal. In this model, we can accommodate the diphoton events through the direct and/or cascade decays of pseudo-scalar and real scalar partners of the complex scalar field. We show that mono-jet searches and gamma-ray observations are complementary in constraining the region where the width of the diphoton resonance can be enhanced due to the couplings of the resonance to dark matter and the correct relic density is obtained. In the case of cascade decay of the resonance, the effective couplings of singlet scalars can be smaller, but the model is still testable by the future discrimination between single photon and photon-jet at the LHC as well as the gamma-ray searches for the cascade annihilation of dark matter.