Abstract
We systematically examine various proposals which aim at increasing the
accuracy in the determination of the renormalization of two-fermion lattice
operators. We concentrate on three finite quantities which are particularly
suitable for our study: the renormalization constants of the vector and axial
currents and the ratio of the renormalization constants of the scalar and
pseudoscalar densities. We calculate these quantities in boosted perturbation
theory, with several running boosted couplings, at the öptimal" scale q*. We
find that the results of boosted perturbation theory are usually (but not
always) in better agreement with non-perturbative determinations of the
renormalization constants than those obtained with standard perturbation
theory. The finite renormalization constants of two-fermion lattice operators
are also obtained non-perturbatively, using Ward Identities, both with the
Wilson and the tree-level Clover improved actions, at fixed cutoff (\$\beta\$=6.4
and 6.0 respectively). In order to amplify finite cutoff effects, the quark
masses (in lattice units) are varied in a large interval 0<am<1. We find that
discretization effects are always large with the Wilson action, despite our
relatively small value of the lattice spacing (\$a^-1 3.7\$ GeV). With
the Clover action discretization errors are significantly reduced at small
quark mass, even though our lattice spacing is larger (\$a^-1 2\$ GeV).
However, these errors remain substantial in the heavy quark region. We have
implemented a proposal for reducing O(am) effects, which consists in matching
the lattice quantities to their continuum counterparts in the free theory. We
find that this approach still leaves appreciable, mass dependent,
discretization effects.
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