Higher-order corrections to precision observables in the Standard Model and the MSSM

A summary of recent results obtained for higher-order corrections to precision observables in the Standard Model and the Minimal Supersymmetric Standard Model is given. In the Standard Model electroweak two-loop 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 order. Furthermore the Higgs-mass dependence of the two-loop corrections to the relation between the gauge-boson masses is analyzed. In the MSSM the exact gluonic corrections to ∆r are derived. They are compared with the leading contribution entering via the ρ parameter. 1 Talk presented at the XXI School of Theoretical Physics, “Recent progress in theory and phenomenology of fundamental interactions”, Ustron, September 19–24, 1997.