Abstract
Motivated by the 750 GeV diphoton excess found at LHC, we compute the maximal width into $\gamma\gamma$ that a neutral scalar can acquire through a loop of charged fermions or scalars as function of the maximal scale at which the theory holds, taking into account vacuum (meta)stability bounds. We show how an extra gauge symmetry can qualitatively weaken such bounds, and explore collider probes and connections with Dark Matter.
Highlights
In the scalar case, the loop that mediates S → γγ can be enhanced by a large cubic κS|X|2 [9,10,11]
A large cubic leads to extra minima in the potential V (S, X) and is thereby subject to vacuum stability bounds
In this work we consider absolute stability and meta-stability. After imposing such bounds, the maximal Γγγ given by a scalar loop is similar to the maximal Γγγ produced by a fermion loop
Summary
Assuming g = 0 and ignoring eq (2.3d) we reproduce the results of [3, 7, 8], that we plot in figure 1 as the maximal value of Γγγ as function of the Landau poles scale. Combining eq (2.2) with eq (2.3a) shows that the maximal Γγγ is obtained for small N = 1 and for Y as large as allowed by Landau poles for hypercharge, which corresponds to uninteresting values Y ∼ 10. Perturbative g allows to obtain qualitatively larger values of y and thereby of Γγγ without hitting Landau poles than in the g = 0 limit.
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