O(α2GFmt2) contributions to H → γγ

The rare decay H → γγ is a promising detection channel for an intermediate mass Higgs boson. We compute its two-loop O(α2GFmt2) correction in the standard model and find that the relative correction to the decay rate runs between 0.7% and 0.5% for MH = 80−150 GeV, which is of the same order as the corresponding QCD correction. The analogous correction to the amplitude for gg → H is recovered as a special case. The generalization of our result to other models is also briefly indicated.