Wilson fermions quark bilinears to three loops
  Quark currents renormalization constants can in principle be safely computed in lattice perturbation theory. In practice, traditional lattice perturbative computations are quite cumbersome, so that so far only the first loop results were available. By making use of Numerical Stochastic Perturbation Theory we reached three (and with less statistical precision even four) loops, both in quenched and in unquenched theory. Convergence properties of the series can be assessed and omparison with non perturbative results (where available) can be made: high loops computations of renormalization constants can be a valuable tool for lattice QCD. 
F. Di Renzo, A. Mantovi, V. Miccio, C. Torrero and L. Scorzato