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 ${\mathit{m}}_{\mathit{t}}$=150 GeV and ${\mathit{M}}_{\mathit{H}}$=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 α, ${\mathit{G}}_{\mathit{F}}$, and ${\mathit{M}}_{\mathit{Z}}$ (${\mathit{G}}_{\mathit{F}}$, ${\mathit{M}}_{\mathit{W}}$, and ${\mathit{M}}_{\mathit{Z}}$) as input parameters. Out of the above results, -8.5% is due to QCD. The ${\mathit{m}}_{\mathit{t}}$ and ${\mathit{M}}_{\mathit{H}}$ dependence is given up to 300 and 1000 GeV, respectively. The inadequacy of a leading ${\mathit{m}}_{\mathit{t}}$ calculation is pointed out.