Abstract
We discuss some consistency tests that must be passed for a successful explanation of a diphoton excess at larger mass scales, generated by a scalar or pseudoscalar state, possibly of a composite nature, decaying to two photons. Scalar states at mass scales above the electroweak scale decaying significantly into photon final states generically lead to modifications of Standard Model Higgs phenomenology. We characterise this effect using the formalism of Effective Field Theory (EFT) and study the modification of the effective couplings to photons and gluons of the Higgs. The modification of Higgs phenomenology comes about in a variety of ways. For scalar $0^+$states, the Higgs and the heavy boson can mix. Lower energy phenomenology gives a limit on the mixing angle, which gets generated at one loop in any such theory explaining the diphoton excess. Even if the mixing angle is set to zero, we demonstrate that a relation exists between lower energy Higgs data and a massive scaler decaying to diphoton final states. If the new boson is a pseudoscalar, we note that if it is composite, it is generic to have an excited scalar partner that can mix with the Higgs, which has a stronger coupling to photons. In the case of a pseudoscalar, we also characterize how lower energy Higgs phenomenology is directly modified using EFT, even without assuming a scalar partner of the pseudoscalar state. We find that naturalness concerns can be accommodated, and that pseudoscalar models are more protected from lower energy constraints.
Highlights
Our motivation is the report of a slight excess of diphoton events in the ATLAS and CMS data [1, 2] at ∼ 750 GeV
Scalar states at mass scales above the electroweak scale decaying significantly into photon final states generically lead to modifications of Standard Model Higgs phenomenology
Lower energy phenomenology gives a limit on the mixing angle, which gets generated at one loop in any theory explaining the diphoton excess
Summary
The Landau-Yang theorem [4, 5] states that a resonance decaying to diphotons can only have spin 0 or spin 2. In a fairly general class of models, the scalar field S couples to gluons, photons and possibly quarks in order to explain the production and decay of S into photons that give the diphoton excess. The Cγγ term was reported in [6] to be 0.53 using the equivalent photon approximation, assuming that the inverse of the impact parameter scaled to the proton radius is r ∼ 0.13 This result is similar to the elastic scattering result reported in ref. Recent estimates of the combined inelasticinelastic, elastic-inelastic and elastic-elastic photoproduction [7,8,9] give a corrected Cγγ = 78.3 The latter coefficients were generated in ref. We consider the case where the scalar field S couples via the operators. We note that the running effect on the production and decay of the scalar particle is higher order in the power counting, and neglected. One naturally expects Λg ∼ Λγ and cB and cG to differ only by group theory factors, in scenarios where a common mediator generates the two decays
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