Understanding perturbative results for decays of \tau leptons into   hadrons
  We review some results obtained by us and others concerning the structure of higher order perturbation series in perturbative QCD and their resummation using the renormalization group equation. We illustrate our results by a number of examples involving hadronic \tau decays and e^+ e^- annihilation. 
S. Groote, J. G. K\"orner, A. A. Pivovarov
hep-ph