Power corrections in the single dressed gluon approximation - the average thrust as a case study

Infrared power corrections for Minkowskian QCD observables are analyzed in the framework of renormalon resummation, motivated by analogy with the skeleton expansion in QED and the BLM approach. Performing the ''massive gluon'' renormalon integral a renormalization scheme invariant result is obtained. Various regularizations of the integral are studied. In particular, we compare the infrared cutoff regularization with the standard principal value Borel sum and show that they yield equivalent results once power terms are included. As an example the average thrust < T > in e+e- annihilation is analyzed. We find that a major part of the discrepancy between the known next-to-leading order calculation and experiment can be explained by resummation of higher order perturbative terms. This fact does not preclude the infrared finite coupling interpretation with a substantial 1/Q power term. Fitting the regularized perturbative sum plus a 1/Q term to experimental data yields αsMSbar(MZ) = 0.110 /pm 0.006. (author)