Improved QCD expansion and the problem of determination of alpha_s and the condensates from the tau decays

Abstract

The problem of determination of ${\alpha }_s$ and the condensates from the moments of invariant mass distribution in the semileptonic tau decays is considered. It is investigated how the extracted values of alpha_s(m^{2}_{tau}) and the condensates are affected by the the renormalization scheme dependence of the next-to-next-to-leading order perturbative corrections to the spectral moments. A simplified approach is used, in which the nonperturbative contributions are approximated by the terms of dimension six in the SVZ expansion, which arise from the four-quark condensates. \\

Comments: 4 pages Latex, to appear in the Proceedings of the High Energy Physics International Euroconference on Quantum Chromodynamics, 3--9 July 1997, Montpellier, France