RI/MOM renormalization window and Goldstone pole contamination

We perform a comparative study of the ratio of lattice (Wilson fermion) renormalization constants Z(P)/Z(S), obtained non-perturbatively from the RI/MOM renormalization conditions and from Ward Identities of on- and off-shell Green's functions. The off-shell Ward Identity used in this work relies on correlation functions with non-degenerate quark masses. We find that, due to discretization effects, there is a 10-15% discrepancy between the two Ward Identity determinations at current bare couplings (beta values). The RI/MOM result is in the same range and has a similar systematic error of 10-15%. Thus, contrary to a previous claim, the contamination of the RI/MOM result from the presence of a Goldstone pole at renormalization scales mu similar to a-(1) is subdominant, compared to finite cutoff effects. (C) 2000 Elsevier Science B.V. All rights reserved.