Study of the Standard Model on the Lattice with Massively Parallel Computer CP-PACS

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This project carried out an extensive Nf=2+1 lattice QCD simulation including dynamical effects of all three light quarks, u, d, s using the fully O(a) improved Wilson-clover quark action and RG-improved gluon action at three lattice spacings a=0.071fm, 0.1fm and 0.12fm. Detailed study was made of the light hadron spectrum, light quark masses and heavy quark physics, taking a systematic continuum extrapolation. The main results are as follows :(1) Light hadron spectrumIn quenched QCD a systematic deviation of up to 10% is known to exist in the meson and baryon spectrum. The present calculation has shown that this deviation goes away in the Nf=2+1 calculations, the results showing an agreement with experiment at a 1% level. Systematic errors, however, arising from the fact that quarks are still relatively heavy in the simulations need to be assessed using Wilson chiral perturbation theory. Preliminary analyses show that they are consistent with polynomial extrapolation.(2) Light quark m … More assesThe meson spectrum results allow us to evaluate the light quark masses, for which we find in the continuum limit, m=3.49(15)MeV for the average of u and d quark mass in the MS scheme at μ=2GeV, and m=90.9(3.7)MeV for s quark. These values are about 2/3 of the phenomenologically widely used values.(3) Heavy quark physicsExtensive tests were made of the relativistic heavy quark action proposed by the members of the project. Test calculations in quenched QCD for the bottomonium spectrum and B meson decay constants with a non-perturbative tuning of speed of light showed excellent scaling behavior. Encouraged by the success, calculations on the dynamical Nf=2+1 flavor configurations are being made.(4) Future perspectiveThe results obtained in this project have been presented at Lattice Symposia and various international conferences. A limitation encountered in the present calculation is difficulty of penetrating into the light quark mass region. Application of the domain-decomposed HMC algorithm recently proposed has been tested, and encouraging results were obtained for their use on the next generation PACS-CS computer. Less