Diphoton Excess and Running Couplings

TL;DR

This paper derives a model-independent upper bound on the diphoton production cross section at the LHC based on the relationship between loop contributions to diphoton signals and gauge coupling beta functions, considering running couplings and perturbativity.

Contribution

It establishes a universal upper limit on the diphoton cross section linked to the cutoff scale and particle masses, connecting diphoton signals with gauge coupling running in a model-independent way.

Findings

Derived an upper bound on diphoton cross section based on beta functions.

Linked diphoton signal strength to the perturbativity of Yukawa couplings.

Provided explicit bounds for specific models considering running couplings.

Abstract

The recently observed diphoton excess at the LHC may suggest the existence of a singlet (pseudo-) scalar particle with a mass of 750 GeV which couples to gluons and photons. Assuming that the couplings to gluons and photons originate from loops of fermions and/or scalars charged under the Standard Model gauge groups, we show that here is a model-independent upper bound on the cross section $\sigma(pp\to S\to \gamma\gamma)$ as a function of the cutoff scale $\Lambda$ and masses of the fermions and scalars in the loop. Such a bound comes from the fact that the contribution of each particle to the diphoton event amplitude is proportional to its contribution to the one-loop $\beta$ functions of the gauge couplings. We also investigate the perturbativity of running Yukawa couplings in models with fermion loops, and show the upper bounds on $\sigma(pp\to S\to \gamma\gamma)$ for explicit models.