Renormalization Scheme and Higher Loop Stability in Hadronic $\tau$   Decay within Analytic Perturbation Theory
  We apply an analytic description to the inclusive decay of the $\tau$ lepton. We argue that this method gives not only a self-consistent description of the process both in the timelike region by using the initial expression for $R_\tau$ and in the spacelike domain by using the analytic properties of the hadronic correlator, but also leads to the fact that theoretical uncertainties associated with unknown higher-loop contributions and renormalization scheme dependence can be reduced dramatically. 
K. A. Milton, I. L. Solovtsov, O. P.Solovtsova, V. I. Yasnov