We present results of a large-scale simulation for the flavor non-singlet light hadron spectrum in quenched lattice QCD with the Wilson quark action. Hadron masses are calculated at four values of lattice spacing in the range a ≈ 0.1 -0.05 fm on lattices with a physical extent of 3 fm at five quark masses corresponding to m π /m ρ ≈ 0.75 -0.4. The calculated spectrum in the continuum limit shows a systematic deviation from experiment, though the magnitude of deviation is contained within 11%. Results for decay constants and light quark masses are also reported.

We present an overview of recent results from the CP-PACS computer on the quenched light hadron spectrum and an on-going two-flavour full QCD study. We find that our quenched hadron mass results are compatible with the mass formulae predicted by quenched chiral perturbation theory, which we adopt in our final analysis. Quenched hadron masses in the continuum limit show unambiguous and systematic deviations from experiment. For our two-flavour full QCD simulation we present preliminary results on the light hadron spectrum, quark masses and the static potential. The question of dynamical sea quark effects in these quantities is discussed.

We define a fixed point topological charge for the two-dimensional O(3) lattice σ-model which is free of topological defects. We use this operator in combination with the fixed point action to measure the topological susceptibility for a wide range of correlation lengths. The results strongly suggest that it is not a physical quantity in this model. The procedure, however, can be applied to other asymptotically free theories as well.

We report on a study of heavy quark bound states containing an additional excitation of the gluonic degrees of freedom. To this end we employ the nonrelativistic QCD approach on coarse and asymmetric lattices, where we discard vacuum polarization effects and neglect all spin-correction terms. We find a clear hybrid signal on all our lattices (a s 0.15, . . . , 0.47 fm). We have studied in detail the lattice spacing artifacts, finite volume effects, and mass dependence. Within the above approximations we predict the lowest lying hybrid excitation in charmonium to be 1.323(13) GeV above the ground state, where we use the 1P-1S splitting to set the scale. The bottomonium hybrid was found to be 1.542(8) GeV above its ground state. [S0031-9007(99)

A lattice study of the equation of state for pure SU͑3͒ gauge theory using a renormalization-group ͑RG͒ improved action is presented. The energy density and pressure are calculated on a 16 3 ϫ4 and a 32 3 ϫ8 lattice employing the integral method. Extrapolating the results to the continuum limit, we find the energy density and pressure to be in good agreement with those obtained with the standard plaquette action within the error of 3-4 %. ͓S0556-2821͑99͒07819-4͔