HIGHER-ORDER QCD AND QUARK MASS CORRECTIONS TO THE Z-WIDTHS IN THE STANDARD MODEL

We estimate, in the MSBAR scheme, the strengths of the higher order QCD (alpha-s2, alpha-s3) and quark mass (m(f)2, m(f)4, alpha-s(m(f)2, m(f)4)) corrections to the Z widths in the standard model (SM). Then, we give improved SM predictions of these widths. The observables GAMMA-H/GAMMA-e and sigma-H, which can be predicted and measured accurately are almost insensitive to the changes of the Higgs (40 GeV less-than-or-equal-to M(H) less-than-or-equal-to 1 TeV) and top quark (M(Z) less-than-or-equal-to M(t) less-than-or-equal-to 230 GeV) masses. Then, they should be useful in the high precision tests of the SM. Improved estimates of some quantities related to the bbBAR width which are sensitive to the top quark mass are also given.