Development of Research on the Standard Model on the Lattice using the Massively Parallel Computer CP-PACS

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This research program aimed to exploit the high computational power of the CP-PACS computer for significantly advancing the study of the non-perturbative aspects of the Standard Model using the lattice formulation of QCD. Specifically, we concentrated on the following subjects :(i) To obtain precise light hadron spectrum in quenced lattice QCD, we carried out an extensive simulation with the standard plaquette gauge action and the Wilson quark action employing large lattices and high statistics. For the first time, we clearly showed that the quenched light hadron spectrum deviates from the experiment by about 10% due to the quenched approximation.(ii) From a systematic study of full GCD with two flavors of light dynamical quarks using an improved action, we showed that the hadron spectrum becomes much closer to experiment than the quenched approximation. The values for light quark masses from full QCD are 20-30% smaller than those in the quenched QCD. The decay constant for B and Bs me … More sons, which are important in a study of the weak interaction, is larger by about 10% in full QCD. The η' meson mass in the continuum limit is close to the experiment, suggesting that the U(1) problem is solved in QCD.(iii) We studied the finite-temperature phase transition and equation of state of QCD using the same improved action as employed in (ii). For the pure gluon theory, we found that the equation of state in the continuum limit agrees well with that obtained with the standard action, demonstrating high reliability of our methods. This work has been extended to full QCD with two flavors of quarks. The phase structure was explored and the equation of state was calculated on an NィイD2tィエD2 = 4 lattice.(iv) Domain-wall QCD offers a possibility to resolve the problem of broken chiral symmetry in the conventional formulations of lattice quarks. As a first step to establish its viability, we studied chiral properties as a function of various parameters of the formalism. We found that exact chiral symmetry is realized for sufficiently fine lattices, while the formalism does not work on coarse lattices. Here, an improved gauge action shows improved chiral symmetry. Work is now extended to calculations of physical matrix elements relevant for CP violation studies. Less