Non-perturbative renormalization of the axial current with dynamical   Wilson fermions
  We present a new normalization condition for the axial current, derived from the PCAC relation with non-vanishing quark mass. This condition is expected to reduce mass effects in the chiral extrapolation of the results for the normalization factor Z_A. The application to the two-flavor theory with improved Wilson fermions shows that this expectation is indeed fulfilled. Using the Schroedinger functional setup we calculate Z_A(g_0^2) as well as the vector current normalization factor Z_V(g_0^2) for beta = 6/g_0^2 >= 5.2. 
Michele Della Morte, Roland Hoffmann, Francesco Knechtli, Rainer   Sommer and Ulli Wolff