Two-loop light fermion contribution to Higgs production and decays

We compute the electroweak corrections due to the light fermions to the production cross section sigma(gg --> H) and to the partial decay widths Gamma(H --> gammagamma) and Gamma(H --> gg). We present analytic results for these corrections that are expressed in terms of Generalized Harmonic Polylogarithms. We find that for the gluon fusion production cross section and for the decay width Gamma(H --> gg) the corrections are large in the Higgs mass region below 160 GeV, where they grow from 4 to 9% of the lowest order term, while above 160 GeV they are small. For the decay width Gamma(H --> gammagamma) the corrections for Higgs mass above 160 GeV are typically below -5% of the lowest order term but they may reach O(-10%) for m(H) similar to 2m(W). (C) 2004 Elsevier B.V. All rights reserved.