A pseudoscalar decaying to photon pairs in the early LHC Run 2 data

TL;DR

This paper investigates whether a pseudoscalar particle at 750 GeV could explain the diphoton excess observed at the LHC, analyzing model requirements, potential theoretical frameworks, and related experimental signatures.

Contribution

It proposes a viable pseudoscalar explanation for the 750 GeV excess, including model considerations and expected signals in other channels.

Findings

A pseudoscalar can account for the diphoton excess with appropriate couplings.

Composite Higgs models can naturally produce a 750 GeV pseudoscalar.

Signals in $Zeta$, $ZZ$, and $WW$ channels are expected if the resonance is a pseudoscalar.

Abstract

In this paper we explore the possibility of a pseudoscalar resonance to account for the 750 GeV diphoton excess observed both at ATLAS and at CMS. We analyze the ingredients needed from the low energy perspective to obtain a sufficiently large diphoton rate to explain the signal while avoiding constraints from other channels. Additionally, we point out composite Higgs models in which one can naturally obtain a pseudoscalar at the 750 GeV mass scale and we estimate the pseudoscalar couplings to standard model particles that one would have in such models. A generic feature of models that can explain the excess is the presence of new particles in addition to the 750 GeV state. Finally, we note that due to the origin of the coupling of the resonance to photons, one expects to see comparable signals in the $Z\gamma$, $ZZ$, and $WW$ channels.