TTP07-05 Two-Loop Formfactors in Theories with Mass Gap and Z-Boson Production

The non-factorizable two-loop corrections to the formfactor both for a $U(1)\times U(1)$ and a $SU(2)\times U(1)$ gauge theory with massive and massless gauge bosons respectively are evaluated at arbitrary momentum transfer $q^2$. The asymptotic behaviour for $q^2\to\infty$ is compared to a recent calculation of Sudakov logarithms. The result is an important ingredient for the calculation of radiative corrections to $Z$-boson production at hadron and lepton colliders.