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 scales of about 2 GeV is subdominant, compared
to finite cutoff effects.Comment: LATEX, 12 pages final version to appear on Phys. Lett.
