A quark action for very coarse lattices

We investigate a tree-level O(a^3)-accurate action, D234c, on coarse lattices. For the improvement terms we use tadpole-improved coefficients, with the tadpole contribution measured by the mean link in Landau gauge. We measure the hadron spectrum for quark masses near that of the strange quark. We find that D234c shows much better rotational invariance than the Sheikholeslami-Wohlert action, and that mean-link tadpole improvement leads to smaller finite-lattice-spacing errors than plaquette tadpole improvement. We obtain accurate ratios of lattice spacings using a convenient ``Galilean quarkonium'' method. We explore the effects of possible O(alpha_s) changes to the improvement coefficients, and find that the two leading coefficients can be independently tuned: hadron masses are most sensitive to the clover coefficient, while hadron dispersion relations are most sensitive to the third derivative coefficient C_3. Preliminary non-perturbative tuning of these coefficients yields values that are consistent with the expected size of perturbative corrections.Comment: 22 pages, LaTe

Flavor Singlet Meson Mass in the Continuum Limit in Two-Flavor Lattice QCD

We present results for the mass of the eta-prime meson in the continuum limit for two-flavor lattice QCD, calculated on the CP-PACS computer, using a renormalization-group improved gauge action, and Sheikholeslami and Wohlert's fermion action with tadpole-improved csw. Correlation functions are measured at three values of the coupling constant beta corresponding to the lattice spacing a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams are evaluated using a noisy source method. We calculate eta-prime propagators using local sources, and find that excited state contributions are much reduced by smearing. A full analysis for the smeared propagators gives metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.Comment: 9 pages, 19 figures, 4 table