Two and three loops computations of renormalization constants for   lattice QCD
  Renormalization constants can be computed by means of Numerical Stochastic Perturbation Theory to two/three loops in lattice perturbation theory, both in the quenched approximation and in the full (unquenched) theory. As a case of study we report on the computation of renormalization constants of the propagator for Wilson fermions. We present our unquenched (N_f=2) computations and compare the results with non perturbative determinations. 
F. Di Renzo, A. Mantovi, V. Miccio, L. Scorzato, C. Torrero