A Composite Model for the 750 GeV Diphoton Excess

TL;DR

This paper proposes a composite pseudo Nambu-Goldstone boson model to explain the 750 GeV diphoton excess, analyzing its particle spectrum, experimental signatures, and implications for physics beyond the Standard Model.

Contribution

It introduces a minimal composite model with hidden pions and explores their phenomenology, including experimental constraints and potential explanations for LHC excesses.

Findings

Two hidden pions are near current experimental limits.

The model predicts new resonances accessible at the LHC.

Extensions can produce additional singlet resonances for various excesses.

Abstract

We study a simple model in which the recently reported 750 GeV diphoton excess arises from a composite pseudo Nambu-Goldstone boson---hidden pion---produced by gluon fusion and decaying into two photons. The model only introduces an extra hidden gauge group at the TeV scale with a vectorlike quark in the bifundamental representation of the hidden and standard model gauge groups. We calculate the masses of all the hidden pions and analyze their experimental signatures and constraints. We find that two colored hidden pions must be near the current experimental limits, and hence are probed in the near future. We study physics of would-be stable particles---the composite states that do not decay purely by the hidden and standard model gauge dynamics---in detail, including constraints from cosmology. We discuss possible theoretical structures above the TeV scale, e.g. conformal dynamics and supersymmetry, and their phenomenological implications. We also discuss an extension of the minimal model in which there is an extra hidden quark that is singlet under the standard model and has a mass smaller than the hidden dynamical scale. This provides two standard model singlet hidden pions that can both be viewed as diphoton/diboson resonances produced by gluon fusion. We discuss several scenarios in which these (and other) resonances can be used to explain various excesses seen in the LHC data.