Speaker
Description
In this talk three-loop QCD corrections to heavy quark form factors
are presented. They constitute the virtual corrections for various
processes as, e.g., top quark production in $e^+ e^-$ annihilation or
Higgs decay into heavy quarks. A semi-numerical method is discussed,
which is based on expansions around singular and regular kinematical
points. They are matched at intermediate values of the squared
partonic center-of-mass energy $s$ which allows to cover the whole
kinematic range. The method permits a systematic increase of the
precision by varying the expansion depth and the choice of the
intermediate matching points. Results are presented for various
choices of external currents.