STRONG SUPERSYMMETRIC QUANTUM EFFECTS ON THE TOP-QUARK WIDTH

We compute the one-loop supersymmetric QCD quantum effects on the widt h Gamma(t --> W+ b) of the canonical main decay of the top quark withi n the framework of the MSSM. The corrections can be of either sign dep ending on whether the stop squark mass is above or below the top quark decay threshold into stop and gluino Gamma(t --> (tg) over tilde). Fo r m(i) above that threshold, the corrections are negative and can be o f the same order (and go in the same direction) as the ordinary QCD co rrections, even for stop and gluino masses of O(100) GeV. Since the el ectroweak supersymmetric quantum effects turn out to be also of the sa me sign and could be of the same order of magnitude, the total MSSM co rrection to the top quark width could potentially result in a rather l arge O(10-25)% reduction of Gamma(t --> W+ b) far beyond the conventio nal QCD expectations.