Incorporation of QCD effects in basic corrections of the electroweak theory

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Abstract
We study the incorporation of QCD effects in the basic electroweak corrections Δ^r, Δ^rW, and Δr. They include perturbative O(ααs) contributions and t¯t threshold effects. The latter are studied in the resonance and Green-function approaches, in the framework of dispersion relations that automatically satisfy relevant Ward identities. Refinements in the treatment of the electroweak corrections, in both the modified minimal subtraction (−−−−MS) and the on-shell schemes of renormalization, are introduced, including the decoupling of the top quark in certain amplitudes, its effect on ^e2(mZ) and sin2^θW(mZ), the incorporation of recent results on the leading irreducible O(α2) corrections, and simple expressions for the residual, i.e., "nonelectromagnetic," parts of Δ^r, Δ^rW, and Δr. The results are used to obtain accurate values for mW and sin2^θW(mZ), as functions of mt and mH. The higher-order effects induce shifts in these parameters comparable to the expected experimental accuracy, and they increase the prediction for mt derived from current measurements. The −−−−MS and the on-shell calculations of Δr, in a recently proposed formulation, are compared and found to be in excellent agreement over the wide ranges 60 GeV≤mH≤1 TeV, mZ≤mt≤250 GeV
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