Two-loop electroweak contributions to $\Delta r$

Abstract

A review is given on the quantum correction $\Delta r$ in the $W$--$Z$ mass correlation at the electroweak two-loop level, as derived from the calculation of the muon lifetime in the Standard Model. Exact results for $\Delta r$ and the $W$-mass prediction including ${\mathcal{O}}(\alpha^2)$ corrections with fermion loops are presented and compared with previous results of a next-to-leading order expansion in the top-quark mass.Comment: 14 pages, including 4 figures. Presented at the 5th International Symposium on Radiative Corrections, (RADCOR-2000), Carmel CA, USA, 11-15 September 200