Pa. Raczka et A. Szymacha, IMPROVED ANALYSIS OF THE RENORMALIZATION SCHEME AMBIGUITIES IN THE QCD CORRECTIONS TO THE SEMILEPTONIC DECAY OF THE TAU-LEPTON, Zeitschrift fur Physik. C, Particles and fields, 70(1), 1996, pp. 125-132
The perturbative QCD corrections to the semileptonic decay width of th
e tau lepton are evaluated in the next-next-to-leading order from the
contour integral representation in various renormalization schemes, us
ing numerical solution of the renormalization group equation for compl
ex energies. A quantitative estimate of the ambiguities resulting from
the freedom of choice of the renormalization scheme is obtained by ta
king into account predictions in all schemes that do not involve large
cancellations in the expression for the scheme invariant combination
of the expansion coefficients. The problem of an optimal choice of the
renormalization scheme for the improved perturbative expression is di
scussed. A fit of Lambda((M) over bar (S) over bar)is made using the a
vailable experimental data.