On the contribution from the light quarks to $H\to\gamma\gamma , \gamma Z$

Abstract

This Letter addresses the contribution from the light $u , d , s$ quarks to the amplitudes for the decay modes of the Brout-Englert-Higgs scalar boson $H$ into two photons ($H\to\gamma\gamma$) or to a photon and a neutral weak gauge boson ($H\to\gamma Z$), taking into account the non-perturbative aspects of QCD. Contrary to a recent claim, the contribution from the light quarks does not vanish. Rather, it is shown that, in contrast to the perturbative evaluations usually considered in the literature, this contribution to the amplitudes starts with a term that is linear, and not quadratic, in the masses of the light quarks, thus pointing toward a sizeable enhancement of their contribution to $H \to \gamma \gamma$.