NONPERTURBATIVE EXPANSION, RENORMALONS, AND TAU-DECAY

We analyze inclusive tau-decay using a modified version of the a expan sion, a nonperturbative technique in which the effective coupling is a nalytic in the infrared region. The modification involves renormalizat ion group improvement of the integrand in a spectral representation fo r the D-function prior to implementing the a expansion. The advantage of this approach is that it enables us to monitor the structure of the induced power corrections and to ensure that these are consistent wit h the operator product expansion. Numerically the method agrees well w ith experiment: the comparison is made with the physical quantity R-z using R-tau as input.