VIRTUAL TOP-QUARK EFFECTS ON THE H-]B(B)OVER-BAR DECAY AT NEXT-TO-LEADING ORDER IN QCD

By means of a heavy-top-quark effective Lagrangian, we calculate the t hree-loop corrections of O (alpha(s)(2)G(F)(.)M(t)(2)) to the <H --> ( b)over bar b> partial decay width of the standard-model Higgs boson wi th intermediate mass M-H much less than 2M(t). We take advantage of a soft-Higgs theorem to construct the relevant coefficient functions. We present our result both in the <(MS)over bar> and on-shell schemes of mass renormalization. The <(MS)over bar> formulation turns out to be favorable with regard to the convergence behavior. We also test a rece nt idea concerning the naive nonabelianization of QCD.