HIGHER-ORDER CORRECTIONS TO PRECISION OBSERVABLES IN THE STANDARD MODEL AND THE MSSM

A summary of recent results obtained for higher-order corrections to p recision observables in the Standard Model and the Minimal Supersymmet ric Standard Model is given. In the Standard Model, electroweak two-lo op results valid for arbitrary values of the masses of the top quark, the Higgs boson and the gauge bosons are discussed. For the example of two specific diagrams the exact two-loop result is compared with the result of an expansion in the top-quark mass up to next-to-leading ord er. Furthermore the Higgs-mass dependence of the two-loop corrections to the relation between the gauge-boson masses is analyzed. In the MSS M, the gluonic corrections to Delta r are derived. They are compared w ith the leading contribution entering via the rho parameter.