An approach for evaluation of observables in analytic versions of QCD
  We present two variants of an approach for evaluation of observables in analytic QCD models. The approach is motivated by the skeleton expansion in a certain class of schemes. We then evaluate the Adler function at low energies in one variant of this approach, in various analytic QCD models for the coupling parameter, and compare with perturbative QCD predictions and the experimental results. We introduce two analytic QCD models for the coupling parameter which reproduce the measured value of the semihadronic tau decay ratio. Further, we evaluate the Bjorken polarized sum rule at low energies in both variants of the evaluation approach, using for the coupling parameter the analytic QCD model of Shirkov and Solovtsov, and compare with values obtained by the evaluation approach of Milton et al. and Shirkov. 
Gorazd Cvetic and Cristian Valenzuela