  It is recalled why, as already stated in a previous paper, there seems to be
an inconsistency in identifying the non perturbative ZA,MOM as the
renormalisation of the axial current, or equivalently, in setting as
normalisation condition that the renormalised vertex=1 at p^2 = mu^2 at some
renormalisation scale mu, where p is the momentum in the legs. Indeed, unlike
the vector case, the Ward-Takahashi (WT) identity for the axial current is
shown to imply both the renormalisation scale independence of ZA and a mu2
dependence of ZA,MOM. This mu^2 dependence is simply related to certain
invariants in the pseudoscalar vertex and can persist in the chiral limit due
to the spontaneous breaking of chiral symmetry (pion pole). It is seen clearly
in the mu^2 dependence of some lattice calculations of ZA,MOM/ZV,MOM near the
chiral limit.
