Results for Precision Observables in the Electroweak Standard Model at Two-Loop Order and Beyond

Abstract

Higher-order contributions to the precision observables Δr, \sin^2θ_eff and Γ_l are discussed. The Higgs-mass dependence of the observables is investigated at the two-loop level, and exact results are derived for the Higgs-dependent two-loop corrections associated with fermions. The top-quark corrections are compared with the results obtained by an expansion in the top-quark mass up to next-to-leading order. For the pure fermion-loop contributions to Δr results up to four-loop order are derived. They allow to investigate the validity of the commonly used resummation of the leading fermionic contributions to Δr.

8 pages, 2 figures, presented at the Zeuthen Workshop on Elementary Particle Physics, "Loops and Legs in Gauge Theories", Rheinsberg, April 19-24, 1998, to appear in Acta Phys Pol