No abstract

The renormalization factor relating the bare to the renormalization group invariant quark masses is accurately calculated in quenched lattice QCD using a recursive finite-size technique. The result is presented in the form of a product of a universal factor times another factor, which depends on the details of the lattice theory but is easy to compute, since it does not involve any large scale differences. As a byproduct the Lambda-parameter of the theory is obtained with a total error of 8%.Comment: 36 pages, 8 postscript figures, LaTeX, typo corrected in Table

We study the contributions Σ 0 and Σ 1 , proportional to a 0 and a 1 , to the fermion selfenergy in Wilson's formulation of lattice QCD with UV-filtering in the fermion action. We derive results for m crit and the renormalization factors Z S , Z P , Z V , Z A to 1-loop order in perturbation theory for several filtering recipes (APE, HYP, EXP, HEX), both with and without a clover term. The perturbative series is much better behaved with filtering, in particular tadpole resummation proves irrelevant. Our non-perturbative data for m crit and Z A /(Z m Z P ) show that the combination of filtering and clover improvement efficiently reduces the amount of chiral symmetry breaking -we find residual masses am res = O(10 −2 ).

We report on our calculation of the nucleon axial charge gA in QCD with two flavours of dynamical quarks. A detailed investigation of systematic errors is performed, with a particular focus on contributions from excited states to three-point correlation functions. The use of summed operator insertions allows for a much better control over such contamination. After performing a chiral extrapolation to the physical pion mass, we find gA = 1.223 ± 0.063 (stat) +0.035 −0.060 (syst), in good agreement with the experimental value.