Two-loop electroweak heavy-fermion corrections to Higgs-boson production and decay

The dominant electroweak corrections to the production cross sections and partial decay widths of a light Standard Model Higgs boson, with mass MH ⪡ 2mt, are due to top-quark loops. By means of a low-energy theorem, we study at the two-loop level the leading shifts in the Higgsboson couplings to pairs of light fermions and gauge bosons induced by a sequential isodoublet of high-mass fermions. For tree-level and loop-induced Higgs-boson couplings, these corrections are of relative order O(Gμ2mF4)) and O(GμmF2), respectively, where mF represents a generic heavy-fermion mass, with mF ⪢ MW, MH. Except for the Hbb coupling, all results carry over to the case of the top-quark-induced corrections. We discuss possible phenomenological consequences of our results.