Interpreting 750 GeV diphoton excess in SU(5) grand unified theory

Ketan M Patel,Pankaj Sharma

doi:10.1016/j.physletb.2016.04.006

Abstract

The ATLAS and CMS experiments at the LHC have found significant excess in the diphoton invariant mass distribution near 750 GeV. We interpret this excess in a predictive nonsupersymmetric SU(5) grand unified framework with a singlet scalar and light adjoint fermions. The 750 GeV resonance is identified as a gauge singlet scalar. Both its production and decays are induced by 24 dimensional adjoint fermions predicted within SU(5). The adjoint fermions are assumed to be odd under $Z_2$ symmetry which forbids their direct coupling to the standard model fermions. We show that the observed diphoton excess can be explained with sub-TeV adjoint fermions and with perturbative Yukawa coupling. A narrow width scenario is more preferred while a simultaneous explanation of observed cross section and large total decay width requires some of the adjoint fermions lighter than 375 GeV. The model also provides a singlet fermion as a candidate of cold dark matter. The gauge coupling unification is achieved in the framework by introducing color sextet scalars while being consistent with the proton decay constraint.

Highlights

The first set of data collected by ATLAS and CMS experiments at the Large Hadron Colli√der (LHC) with proton–proton collisions at center-of-mass energy s = 13 TeV has recently been presented by the respective collaborations [1]
We show that such a framework can account for large enough cross section of diphoton events observed at the LHC
The BR(S → γ γ ) is much larger for this mass range of adjoint fermions which allows values of coupling |λS | to be as small as ∼ O(0.3) to explain the observed diphoton excess as it can be seen from Fig. 3

Summary

Introduction

The first set of data collected by ATLAS and CMS experiments at the Large Hadron Colli√der (LHC) with proton–proton collisions at center-of-mass energy s = 13 TeV has recently been presented by the respective collaborations [1] Both the experiments claim an excess in the diphoton channel at the invariant mass near 750 GeV. The scalar S can be produced through gluon–gluon fusion at 1-loop and can decay into two photons through similar triangle diagrams with adjoint fermions in the loop We show that such a framework can account for large enough cross section of diphoton events observed at the LHC. We discuss both the narrow and broad width scenarios of diphoton excess provided by the different ranges of the masses of adjoint fermions.

The model

Fitting diphoton excess

Gauge coupling unification and proton decay

Summary and outlook