  If the di-photon excess at 750 GeV hinted by the 2015 data at the LHC is
explained in terms of a scalar resonance participating in the breaking of the
electro-weak symmetry, this resonance must be accompanied by other scalar
states for perturbative unitarity in vector boson scattering to be preserved.
The simplest set-up consistent with perturbative unitarity and with the data of
the di-photon excess is the Georgi-Machacek model.
