De. Soper et Lr. Surguladze, TOP-QUARK CONTRIBUTION TO HADRONIC DECAYS OF THE Z-BOSON AT O(ALPHA(2)(S)) IN QCD, Physical review letters, 73(22), 1994, pp. 2958-2961
We evaluate the effect of a virtual top quark on the coefficient of al
pha(s)(2) in the decay rates Gamma(Z --> hadrons) and Gamma(Z --> b (b
) over bar). We treat the dependence on the top quark mass exactly ins
tead of using a large mass expansion. The present work completes the e
valuation of the alpha(s)(2) contributions to these quantities. The ca
lculation uses both the modified minimal subtraction and Collins-Wilcz
ek-Zee renormalization prescriptions. The results can be applied to th
e hadronic decays of the tau lepton.