MEAN-LINK TADPOLE IMPROVEMENT OF SW AND D234 ACTIONS

We investigate a tadpole-improved tree-level-O(a(3))-accurate action, D234c, on coarse lattices, using the mean link in Landau gauge to meas ure the tadpole contribution. We find that D234e shows much better rot ational invariance than Sheikholeslami-Wohlert, and that mean-link tad pole improvement gives much better hadron mass scaling than plaquette tadpole improvement, with finite-a errors at 0.25 fm of only a few per cent. We explore the effects of possible O(a(s)) changes to the improv ement coefficients, and find that the two leading coefficients can be independently tuned: hadron masses are only sensitive to the clover co efficient C-F, while hadron dispersion relations are only sensitive to the third derivative coefficient C-3. Preliminary non-perturbative tu ning of these coefficients yields values that are consistent with the expected size of perturbative corrections.