Status of the CP-PACS Project

The CP-PACS computer with a peak speed of 300 Gflops was completed in March 1996 and has started to operate. We describe the final specification and the hardware implementation of the CP-PACS computer, and its performance for QCD codes. A plan of the grade-up of the computer scheduled for fall of 1996 is also given.Comment: Talk presented at LATTICE96(machines), 3 pages including 5 PS figure

Two-Nucleon Bound States in Quenched Lattice QCD

We address the issue of bound state in the two-nucleon system in lattice QCD. Our study is made in the quenched approximation at the lattice spacing of a = 0.128 fm with a heavy quark mass corresponding to m_pi = 0.8 GeV. To distinguish a bound state from an attractive scattering state, we investigate the volume dependence of the energy difference between the ground state and the free two-nucleon state by changing the spatial extent of the lattice from 3.1 fm to 12.3 fm. A finite energy difference left in the infinite spatial volume limit leads us to the conclusion that the measured ground states for not only spin triplet but also singlet channels are bounded. Furthermore the existence of the bound state is confirmed by investigating the properties of the energy for the first excited state obtained by 2x2 diagonalization method. The scattering lengths for both channels are evaluated by applying the finite volume formula derived by Luscher to the energy of the first excited states.Comment: 34 pages, 28 figure

An Exploratory Study of Nucleon-Nucleon Scattering Lengths in Lattice QCD

An exploratory study is made of the nucleon-nucleon $s$-wave scattering lengths in quenched lattice QCD with the Wilson quark action. The $\pi$-$N$ and $\pi$-$\pi$ scattering lengths are also calculated for comparison. The calculations are made with heavy quarks corresponding to $m_\pi/m_\rho\approx 0.73-0.95$. The results show that the $N$-$N$ system has an attractive force in both spin-singlet and triplet channels, with their scattering lengths significantly larger than those for the $\pi$-$N$ and $\pi$-$\pi$ cases, a trend which is qualitatively consistent with the experiment. Problems toward a more realistic calculation for light quarks are discussed.Comment: 9 pages. Latex file. Figures are also included as ps file

The Light Quark Masses with the Wilson Quark Action using Chiral Ward Identities

We present results for the light quark masses for the Wilson quark action obtained with the PCAC relation for the one-link extended axial vector current in quenched QCD at $\beta=5.9-6.5$. This method leads to a remarkable improvement of scaling behavior of the light quark masses compared to the conventional method. We obtain ${\bar m}_l=3.87(37)$MeV for the averaged up and down quark mass and ${\bar m}_s=97(9)$MeV for the strange quark mass in the {\barMS} scheme at $\mu=2$GeV.Comment: 3 pages, latex source-file, 2 figures as epsf-file, uses espcrc2.sty. Poster presented at Lattice 97: 15th International Symposium on Lattice Field Theory, Edinburgh, Scotland, 22-26 Jul 199

Two-Flavor Chiral Phase Transition in Lattice QCD with the Kogut-Susskind Quark Action

A summary is presented of a scaling study of the finite-temperature chiral phase transition of two-flavor QCD with the Kogut-Susskind quark action based on simulations on $L^3\times4$ ($L$=8, 12 and 16) lattices at the quark mass of $m_q=0.075, 0.0375, 0.02$ and 0.01. We find a phase transition to be absent for $m_q\geq 0.02$, and also quite likely at $m_q=0.01$. The quark mass dependence of susceptibilities is consistent with a second-order transition at $m_q=0$. The exponents, however, deviate from the O(2) and O(4) values theoretically expected.Comment: 3 pages, Latex(espcrc2,epsf), 3 ps figures, Poster presented at Lattice 9

The end point of the first-order phase transition of the SU(2) gauge-Higgs model on a four-dimensional isotropic lattice

We report results of a study of the end point of the electroweak phase transition of the SU(2) gauge-Higgs model defined on a four-dimensional isotropic lattice with N_t=2. Finite-size scaling study of Lee-Yang zeros yields lambda_c=0.00116(16) for the end point. Combined with a zero-temperature measurement of Higgs and W boson masses, this leads to M_{H,c}=68.2+-6.6 GeV for the critical Higgs boson mass. An independent analysis of Binder cumulant gives a consistent value lambda_c=0.00102(3) for the end point.Comment: LATTICE98(electroweak), 3 pages of LaTeX, 4 figure

Light quark masses from unquenched lattice QCD

We calculate the light meson spectrum and the light quark masses by lattice QCD simulation, treating all light quarks dynamically and employing the Iwasaki gluon action and the nonperturbatively O(a)-improved Wilson quark action. The calculations are made at the squared lattice spacings at an equal distance a^2~0.005, 0.01 and 0.015 fm^2, and the continuum limit is taken assuming an O(a^2) discretization error. The light meson spectrum is consistent with experiment. The up, down and strange quark masses in the \bar{MS} scheme at 2 GeV are \bar{m}=(m_{u}+m_{d})/2=3.55^{+0.65}_{-0.28} MeV and m_s=90.1^{+17.2}_{-6.1} MeV where the error includes statistical and all systematic errors added in quadrature. These values contain the previous estimates obtained with the dynamical u and d quarks within the error.Comment: 4 pages, 3 figures, revtex4; v2: contents partly modified, published versio