Abstract
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.
Highlights
Irrespective of whether it will stay or not, the recent excess in the 2015 LHC data with two photons in the final state at an invariant mass of about 750 GeV [1] reminds us that even after the discovery of the Higgs boson we may still not know all the details of the breaking of the electroweak (EW) symmetry
If the diphoton 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 electroweak symmetry, this resonance must be accompanied by other scalar states for perturbative unitarity in vector-boson scattering to be preserved
The custodial singlet of the model is responsible for the diphoton excess; it is mainly produced in the diphoton fusion channel, and its loop-induced coupling to the photon pairs is enhanced by the doubly charged scalar with its large coupling to the custodial singlet
Summary
Irrespective of whether it will stay or not, the recent excess in the 2015 LHC data with two photons in the final state at an invariant mass of about 750 GeV [1] reminds us that even after the discovery of the Higgs boson we may still not know all the details of the breaking of the electroweak (EW) symmetry. The simplest ( perhaps least interesting) possibility is that this resonance takes no part in the breaking of the EW symmetry In this case, it is possible to reproduce the diphoton excess by coupling the resonance—in a generic fashion—to extra scalar or fermionic degrees of freedom It is possible to reproduce the diphoton excess by coupling the resonance—in a generic fashion—to extra scalar or fermionic degrees of freedom If neither of the above is the case, perturbative unitarity cannot be preserved and the singlet resonance must belong to a nonperturbative regime. This would imply the exciting discovery of a new interaction that is strong at the EW scale. MARCO FABBRICHESI and ALFREDO URBANO model satisfying these requirements that explains the diphoton excess at the LHC for a realistic choice of its parameters
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