THE DECAY-RATE ASYMMETRY OF THE TOP-QUARK

The asymmetries A(k) = [GAMMA(t --> W+d(k))-GAMMA(tBAR --> W-d(k)BAR)] /[GAMMA(t --> W+d(k))+GAMMA(tBAR --> W-d(k)BAR)] in the partial widths of the top quark decays are discussed within the Standard Model (SM), the Two-Higgs-Doublet Model (2HDM) and supersymmetric extensions of t he SM (SSM). The leading contributions to these asymmetries in the SM and in the 2HDM are induced by the up-type quark self-energy diagrams and are found to be very small. However, in the SSM, the asymmetry A(b ) can be substantial, O (alpha(QCD)), provided the CP-violating phase of gluino-top-stop couplings is not suppressed. Within the SSM A(b) is generated by the vertex corrections.