A New Approach to QCD Sum Rules and Inclusive $\tau$ Decay
  We show that renormalization group improvement, making use of analyticity and the structure of the operator product expansion, combined with a non-perturbative expansion method allows one to describe quarkonium states via QCD sum rules without the need for explicit power corrections. This technique also allows an accurate determination of parameters related to the inclusive decay of the $\tau$ lepton. 
H. F. Jones, A. Ritz, and I. L. Solovtsov