Three-loop non-diagonal current correlators in QCD and NLO corrections to single-top-quark production

The non-diagonal correlators of vector and scalar currents are considered a t three-loop order in QCD. The full mass dependence is computed in the case where one of the quarks is massless and the other one carries the mass M. As applications we consider the single-top-quark production via the process q (q) over bar --> t (b) over bar and the decay rate of a charged Higgs in to hadrons. In both cases the computed NLO corrections are shown to be nume rically much less important than the leading ones. (C) 2001 Published by El sevier Science B.V.