RADIATIVE-CORRECTIONS TO TOP-QUARK DECAY

We calculate all radiative corrections to one-loop order for the main decay of the top quark, t --> b + W, in the standard model, retaining exact dependence on all masses. For m(t) = 150 GeV and M(H) = 100 GeV we find a -2.9% ( -6.9%) correction with a very weak dependence on the Higgs-boson mass, in renormalization schemes that use alpha, G(F), and M(Z) (G(F), M(W), and M(Z) as input parameters. Out of the above results, -8.5% is due to QCD. The m(t), and M(H) dependence is given up to 300 and 1000 GeV, respectively. The inadequacy of a leading m(t) calculation is pointed out.