Renormalization schemes and renormalons
  We describe some ways how higher order corrections can reveal themselves if integrated over the infrared region. We show that in different renormalization group (RG) schemes and for some observables one has no factorial divergences. We argue that for treating things in the infrared region it is preferable to start with a RG scheme without the infrared Landau pole in the running coupling constant. The uncertainties for the $\tau$ lepton width resulting from accounting for higher order corrections are discussed. 
N.V. Krasnikov, A.A. Pivovarov