Broad Diphotons from Narrow States

TL;DR

This paper proposes a weakly coupled model where a broad diphoton resonance at 750 GeV arises from off-shell production of narrow particles, explaining recent experimental excesses with a novel decay mechanism.

Contribution

It introduces simplified models and a minimal UV completion that produce broad diphoton signals from narrow states, with distinctive experimental signatures.

Findings

Broad resonance can result from off-shell production of narrow particles.

The model predicts asymmetric diphoton peaks with additional missing energy or jets.

The minimal UV completion involves a singlet scalar and heavy vector-like fermions.

Abstract

ATLAS and CMS have each reported a modest diphoton excess consistent with the decay of a broad resonance at ~ 750 GeV. We show how this signal can arise in a weakly coupled theory comprised solely of narrow width particles. In particular, if the decaying particle is produced off-shell, then the associated diphoton resonance will have a broad, adjustable width. We present simplified models which explain the diphoton excess through the three-body decay of a scalar or fermion. Our minimal ultraviolet completion is a weakly coupled and renormalizable theory of a singlet scalar plus a heavy vector-like quark and lepton. The smoking gun of this mechanism is an asymmetric diphoton peak recoiling against missing transverse energy, jets, or leptons.