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A. Ukawa

Publications and source records attributed to A. Ukawa.

At least 181 records · Page 10Linked to original sources
arXiv1997

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.

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arXiv1997

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

We report on a study of two-flavor finite-temperature chiral phase transition employing the Kogut-Susskind quark action and the plaquette gluon action in lattice QCD for a lattice with $N_t=4$ temporal size. Hybrid R simulations of $10^4$ trajectories are made at quark masses of $m_q=0.075, 0.0375, 0.02, 0.01$ in lattice units for the spatial sizes $8^3, 12^3$ and $16^3$. The spatial size dependence of various susceptibilities confirm the previous conclusion of the absence of a phase transition down to $m_q=0.02$. At $m_q=0.01$ an increase of susceptibilities is observed up to the largest volume $16^3$ explored in the present work. We argue, however, that this increase is likely to be due to an artifact of too small a lattice size and it cannot be taken to be the evidence for a first-order transition. Analysis of critical exponents estimated from the quark mass dependence of susceptibilities shows that they satisfy hyperscaling consistent with a second-order transition located at $m_q=0$. The exponents obtained from larger lattice, however, deviate significantly from both those of O(2), which is the exact symmetry group of the Kogut-Susskind action at finite lattice spacing, and those of O(4) expected from an effective sigma model analysis in the continuum limit.

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arXiv1997

Finite-temperature chiral transitions in QCD with the Wilson quark action

We investigate the finite-temperature phase structure and the scaling of the chiral condensate in lattice QCD with two degenerate light quarks, using a renormalization group improved gauge action and the Wilson quark action. We obtain a phase diagram which is consistent with that from the parity-flavor breaking scenario. The scaling relation for the chiral condensate assuming the critical exponents and the scaling function of the three dimensional O(4) model is remarkably satisfied for a wide range of parameters. This indicates that the chiral transition in two flavor QCD is of second order in the continuum limit.

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arXiv1997

CP-PACS Result for the Quenched Light Hadron Spectrum

The quenched hadron spectrum in the continuum obtained with the Wilson quark action in recent simulations on the CP-PACS is presented. Results for the light quark masses and the QCD scale parameter are reported.

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arXiv1997

Full QCD simulation on CP-PACS

A status report is made of an on-going full QCD study on the CP-PACS aiming at a comparative analysis of the effects of improving gauge and quark actions on hadronic quantities and static quark potential. Simulations are made for four action combinations, the plaquette or an RG-improved action for gluons and the Wilson or SW-clover action for quarks, at $a^{-1} \approx 1.1$-1.3GeV and $m_π/m_ρ\approx 0.7$-0.9. Results demonstrate clearly that the clover term markedly reduces discretization errors for hadron spectrum, while adding six-link terms to the plaquette action leads to much better rotational symmetry in the potential. These results extend experience with quenched simulations to full QCD.

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arXiv1997

Scaling Analysis of Chiral Phase Transition for Two Flavors of Kogut-Susskind Quarks

Report is made of a systematic 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. Our finite-size data show that a phase transition is absent for $m_q\geq 0.02$, and quite likely also at $m_q=0.01$. The scaling behavior of susceptibilities as a function of $m_q$ is consistent with a second-order transition at $m_q=0$. However, the exponents deviate from the O(2) or O(4) values theoretically expected.

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arXiv1997

Lattice QCD Calculation of the Kaon B-parameter with the Wilson Quark Action

The kaon B parameter is calculated in quenched lattice QCD with the Wilson quark action. The mixing problem of the Δs=2 four-quark operators is solved non-perturbatively with full use of chiral Ward identities, and this method enables us to construct the weak four-quark operators exhibiting good chiral behavior. We find B_K(NDR, 2GeV)=0.562(64) in the continuum limit, which agrees with the value obtained with the Kogut-Susskind quark action.

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arXiv1996

Finite-Temperature QCD on the Lattice

Recent developments in finite-temperature studies of lattice QCD are reviewed. Topics include (i) tests of improved actions for the pure gauge system, (ii) scaling study of the two-flavor chiral transition and restoration of $U_A(1)$ symmetry with the Kogut-Susskind quark action, (iii) present understanding of the finite-temperature phase structure for the Wilson quark action. New results for finite-density QCD are briefly discussed.

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arXiv1996

Finite-Temperature Phase Structure of Lattice QCD with the Wilson Quark Action for Two and Four Flavors

We present further analyses of the finite-temperature phase structure of lattice QCD with the Wilson quark action based on spontaneous breakdown of parity-flavor symmetry. Results are reported on (i) an explicit demonstration of spontaneous breakdown of parity-flavor symmetry beyond the critical line, (ii) phase structure and order of chiral transition for the case of $N_f=4$ flavors, and (iii) approach toward the continuum limit.

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arXiv1996

Topics in Light Hadron Mass Spectrum in Quenched QCD

Several topics concerning the light hadron spectrum are discussed. Flavor symmetry breaking effects and the problem of quenched chiral logarithm are examined with pion mass data for the Kogut-Susskind quark action, and light meson decay constants for the Wilson action calculated with non-perturbative renormalization constants are discussed. Results for quark masses are also given both for the Kogut-Susskind and Wilson actions.

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arXiv1996

Continuum Limit of the Heavy-Light Decay Constant with the Quenched Wilson Quark Action

We explore the problems in calculating the decay constant for heavy-light mesons using the quenched Wilson quark action for both heavy and light quarks. We find that the continuum limit of the decay constant is reasonably converged among different prescriptions after the continuum limit is taken. A number of technical problems associated with prescriptions are also addressed.

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arXiv1996

Toward the Continuum Limit of $B_K$ with the Quenched Kogut-Susskind Quark Action

We present new results of our ongoing project toward a precision determination of the kaon $B$ parameter with the Kogut-Susskind quark action in quenched QCD. New results taken at $β$=6.4 and $β=5.7$ suggest that an apparently linear $a$ dependence of $B_K$ previously observed for $β=5.85-6.2$ arises from a change of curvature from convex to concave as the lattice spacing is reduced. Fitting data for $β\geq 5.93$ with an $O(a^2)$ form yields $B_K$(NDR,2 GeV)=0.587(7)(17) in the continuum limit. We also describe a finite-size study of $B_K$ at $β=$ 6.0 and 6.4, and a reanalysis of the theoretical argument for $O(a^2)$ behavior.

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arXiv1995

Fate of the Critical Line and Chiral Transition in Finite-Temperature Lattice QCD with the Wilson Quark Action

Finite-temperature phase structure of lattice QCD with the Wilson quark action is analyzed. We show that the critical line at finite temperatures, defined to be the line of vanishing pion screening mass, turns back toward strong coupling, forming a cusp on the $(β, K)$ plane, and that the line of thermal transition runs past the tip of the cusp without touching the critical line. Previous results are discussed in the light of our findings.

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arXiv1995

Proton Spin Structure from Lattice QCD

A lattice QCD calculation of the proton matrix element of the flavor singlet axial-vector current is reported. Both the connected and disconnected contributions are calculated, for the latter employing the variant method of wall source without gauge fixing. From simulations in quenched QCD with the Wilson quark action on a $16^3\times 20$ lattice at $β=5.7$ (the lattice spacing $a\approx 0.14$fm), we find $ΔΣ=Δu+Δd+Δs=+0.638(54)-0.347(46)-0.109(30) = +0.18(10)$ with the disconnected contribution to $Δu$ and $Δd$ equal to $-0.119(44)$, which is reasonably consistent with the experiment.

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arXiv1995

Finite-Temperature Phase Structure of Lattice QCD with Wilson Quark Action

The long-standing issue of the nature of the critical line of lattice QCD with the Wilson quark action at finite-temperatures, defined to be the line of vanishing pion screening mass, and its relation to the line of finite-temperature chiral tansition is examined. Analytical and numerical evidence are presented that the critical line forms a cusp at a finite gauge coupling, and the line of chiral transition runs past the tip of the cusp without touching the critical line. Implications on the continuum limit and the flavor dependence of chiral transition are discussed.

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arXiv1995

Hadron Scattering Lengths in Lattice QCD

Lattice QCD calculation of s-wave hadron scattering lengths in the channels π-π, π-N, K-N, {\bar K}-N and N-N is carried out in the quenched QCD at $β=6/g^2=5.7$. A variant of the method of wall sourceis developed for this purpose, which reduces the computer time by a factor L^3 on an L^3xT lattice compared to the conventional point source method and avoids the Fierz mixing problem. A version of the method in which gauge configurations are not fixed to any gauge can be extended to calculate disconnected quark loop con- tributions in hadron two- and three-point functions. An analytical estimate of statistical errors for this method is worked out, and the magnitude of errors without and with gauge fixing is compared for the case of π-πfour-point functions calculated with the KS quark action. For π-πscattering both I=0 and 2 scattering lengths are evaluated using the KS and Wilson quark actions on a 12^3x20 lattice. For the same size of lattice, π-N, K-N and {\bar K}-N scattering lenghts are calculated with the Wilson quark action. For the π-πand π-N cases simulation results are consistent with the predictions of current algebra and PCAC within one to two standard deviations up to quite heavy quark masses corresponding to $m_π/m_ρ\approx 0.74$, while for the K-N and {\bar K}-N cases the agreement is within a factor of two. For N-N scat- tering simulations with the Wilson action on a 20^4 lattice with heavy quarks with $m_π/m_ρ\approx 0.74-0.95$, where the deuteron is expected to become unbound from a phenomenological study with one-boson exchange potentials, show that the nucleon-nucleon force is attractive for both spin triplet and singlet channels, and that the scattering lengths are substantially larger compared to those for the π-πand π-N cases even for such heavy quarks.

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arXiv1994

Status of the CP-PACS Project

The CP-PACS Project, which started in April 1992, is a five-year plan to develop a massively parallel computer for carrying out research in computational physics with primary emphasis on lattice QCD. This article describes the architectural design of the CP-PACS computer, the entire computing system including the front end and mass storage, and results of benchmarks for the expected performance for lattice QCD applications.

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