The problem of summation of the perturbation expansion in QCD is discussed. It is argued that this expansion is summable by a modified Borel method. The QCD corrections to the semileptonic width of a heavy lepton are considered as an example. The possible differences between the predictions from the resummed expansion and the truncated expansion are illustrated. It is shown that the use of a Borel-type approximant may eliminate certain discrepancy between the theoretical prediction for the $\tau$ lepton and experiment.

• Received 12 July 1990

DOI:https://doi.org/10.1103/PhysRevD.43.R9