PUB - Publikationen an der Universität Bielefeld

The most reliable prediction for the Higgs-boson mass, M(H). is obtained in a fit to the leptonic Z-resonance observables Gamma(1) and (s) over bar(W)(2) combined with the W-boson mass, M(W), and top-quark mass, m(t), measurements. The corresponding bounds on M(H) are independent of potential uncertainties related to R(b), R(c), and alpha(s)(M(Z)(2)), and they are not significantly further improved by including also the experimental information on the inclusive (hadronic and total) Z-boson decays. At the 1 sigma level, we obtain M(H) less than or similar to 360 GeV using (s) over bar(W)(2)(LEP + SLD) and M(H) less than or similar to 540 GeV using (s) over bar(W)(2)(LEP). Our analysis in terms of effective parameters confirms previous conclusions with increased accuracy. In the mass parameter, Delta x, and the mixing parameter, epsilon, pure fermion loops are sufficient, while for the coupling parameter, Delta y, (M(H)-insensitive) bosonic contributions are essential for consistency with experiment, thus providing indirect empirical evidence for the non-Abelian structure of the theory.