Diphoton signature of neutral pseudo-Goldstone boson in the E6CHM at the CERN LHC

The breakdown of the SU(6) global symmetry to its SU(5) subgroup, that contains the standard model (SM) gauge group, in the $E_6$ inspired composite Higgs model (E$_6$CHM) results in a set of pseudo-Nambu-Goldstone bosons (pNGBs). This set, in particular, involves the SM--like Higgs doublet and a SM singlet boson. In the limit when CP is conserved the SM singlet scalar A is a CP-odd state that does not mix with the SM-like Higgs. The interactions of A with exotic matter beyond the SM, which ensures anomaly cancellation and approximate gauge coupling unification, can induce couplings of this pseudoscalar to the SM gauge bosons. As a consequence, we argue that the SM singlet pNGB state can be identified with the 750 GeV diphoton resonance recently reported by the LHC experiments. Such an interpretation requires that either all or some of the exotic states have masses below 1 TeV. We specify the interactions of the SM singlet pNGB state with the exotic vector-like fermions, top quark and SM gauge bosons as well as examining the dependence of the LHC diphoton production cross section, the total width of the pseudoscalar A and its branching ratios on the parameters of the E6CHM.