Rays of light from the LHC

TL;DR

This paper investigates various theoretical models to explain the 13 TeV di-photon resonance observed at the LHC, proposing four viable scenarios involving new particles and decay mechanisms, and discusses their experimental signatures.

Contribution

The paper introduces four novel theoretical models for the di-photon resonance, expanding beyond simple single-resonance explanations and predicting diverse experimental signatures.

Findings

No conflict between 13 TeV signal and 8 TeV constraints.

Four viable models for the di-photon resonance are proposed.

Multiple new states imply rich signatures at LHC Run-2.

Abstract

We consider models for the di-photon resonance observed at ATLAS (with 3.6 fb^{-1}) and CMS (with 2.6 fb^{-1}). We find there is no conflict between the signal reported at 13 TeV, and the constraints from both experiments at 8 TeV with 20.3 fb^{-1}. We make a simple argument for why adding only one new resonance to the standard model (SM) is not sufficient to explain the observation. We explore four viable options: (i): resonance production and decay through loops of messenger fermions or scalars; (ii): a resonant messenger which decays to the di-photon resonance + X; (iii): an edge configuration where A -> B gamma -> C gamma gamma, and (iv): Hidden Valley-like models where the resonance decays to a pair of very light (sub-GeV) states, each of which in turn decays to a pair of collimated photons that cannot be distinguished from a single photon. Since in each case multiple new states have been introduced, a wealth of signatures is expected to ensue at Run-2 of LHC.