Publications (26)67.67 Total impact


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ABSTRACT: We present the details of simulations for the light hadron spectrum in quenched QCD carried out on the CPPACS parallel computer. Simulations are made with the Wilson quark action and the plaquette gauge action on lattices of size 323×56–643×112 at four values of lattice spacings in the range a≈0.1–0.05fm and spatial extent Lsa≈3fm. Hadronic observables are calculated at five quark masses corresponding to mPS/mV≈0.75–0.4, assuming the u and d quarks are degenerate, but treating the s quark separately. We find that the presence of quenched chiral singularities is supported from an analysis of the pseudoscalar meson data. The physical values of hadron masses are determined using mπ, mρ, and mK (or mφ) as input to fix the physical scale of lattice spacing and the u, d, and s quark masses. After chiral and continuum extrapolations, the agreement of the calculated mass spectrum with experiment is at a 10% level. In comparison with the statistical accuracy of 1%–3% and systematic errors of at most 1.7% we have achieved, this demonstrates a failure of the quenched approximation for the hadron spectrum: the hyperfine splitting in the meson sector is too small, and in the baryon sector the octet masses and mass splitting of the decuplet are both smaller than experiment. Light quark masses are calculated using two definitions: the conventional one and the one based on the axialvector Ward identity. The two results converge toward the continuum limit, yielding mud=4.29(14)0.79+0.51MeV where the first error is statistical and the second one is systematic due to chiral extrapolation. The s quark mass depends on the strange hadron mass chosen for input: ms=113.8(2.3)2.9+5.8MeV from mK and ms=142.3(5.8)0+22.0MeV from mφ, indicating again a failure of the quenched approximation. We obtain the scale of QCD, ΛMS̅ (0)=219.5(5.4)MeV with mρ used as input. An O(10%) deviation from experiment is observed in the pseudoscalar meson decay constants.  [Show abstract] [Hide abstract]
ABSTRACT: We present results of a numerical calculation of lattice QCD with two degenerate flavors of dynamical quarks, identified with up and down quarks, and with a strange quark treated in the quenched approximation. The lattice action and simulation parameters are chosen with a view to carrying out an extrapolation to the continuum limit as well as chiral extrapolations. Gauge configurations are generated with a renormalizationgroup improved gauge action and a mean field improved clover quark action at three values of $\beta$ and four sea quark masses. The sizes of lattice are chosen so that the physical spatial size is kept constant. Hadron masses, light quark masses and meson decay constants are measured at five valence quark masses. We also carry out complementary quenched simulations with the same improved actions. The quenched spectrum from this analysis agrees well in the continuum limit with the one of our earlier work using the standard action. We find the twoflavor full QCD meson masses in the continuum limit to be much closer to experimental meson masses than those from quenched QCD. We take these results as manifestations of sea quark effects in twoflavor full QCD. For baryon masses full QCD values for strange baryons are in agreement with experiment, while they differ increasingly with decreasing strange quark content, resulting in a nucleon mass higher than experiment. The pattern suggests finite size effects as a possible origin for this deviation. For light quark masses in the continuum limit we obtain values which are reduced by about 25% compared to the values in quenched QCD. We also present results for decay constants where large scaling violations obstruct a continuum extrapolation. Need for a nonperturbative estimate of renormalization factors is discussed. Comment: RevTeX, 65 pages, 42 figures  [Show abstract] [Hide abstract]
ABSTRACT: Light quark masses are calculated in lattice QCD with two degenerate flavors of dynamical quarks. The calculations are made with improved actions with lattice spacing a = 0.220.11 fm. In the continuum limit we find m(M&Smacr;)(ud)(2 GeV) = 3.44(+0.14)(0.22) MeV using the pi and rho meson masses as physical input, and m(M&Smacr;)(s)(2 GeV) = 88(+4)(6) MeV or 90(+5)(11) MeV with the K or straight phi meson mass as additional input. The quoted errors represent statistical and systematic combined, the latter including those from continuum and chiral extrapolations, and from renormalization factors. Compared to quenched results, two flavors of dynamical quarks reduce quark masses by about 25%.  [Show abstract] [Hide abstract]
ABSTRACT: We present the final results of the CPPACS calculation of the light hadron spectrum and quark masses with two flavors of dynamical quarks. Simulations are made with a renormalizationgroup improved gauge action and a meanfield improved clover quark action for sea quark masses corresponding to mPS/mV ≈ 0.80.6 and the lattice spacing a = 0.220.11 fm. For the meson spectrum in the continuum limit a clearly improved agreement with experiment is observed compared to the quenched case, demonstrating the importance of sea quark effects. For light quark masses we obtain mud (2GeV) = 3.44+0.140.22 MeV and ms (2GeV) = 88+4−6 MeV (Kinput) and ms(2GeV) = 90+5−11 MeV (φinput), which are reduced by about 25% compared to the values in quenched QCD.  [Show abstract] [Hide abstract]
ABSTRACT: We present results for light quark masses from a systematic lattice QCD study with two degenerate flavors of dynamical quarks. Simulations are made with a renormalizationgroup improved gauge action and a meanfield improved clover quark action for sea quark masses corresponding to $m_{\rm PS}/m_{\rm V} \approx 0.8$0.6 and the lattice spacing $a=0.22$0.11 fm. In the continuum limit we find $m_{ud}^{\bar{MS}}(2 {\rm GeV})=3.44^{+0.14}_{0.22}$ MeV using the $\pi$ and $\rho$ meson masses as physical input, and $m_s^{\bar{MS}}(2 {\rm GeV})=88^{+4}_{6}$ MeV or $90^{+5}_{11}$ MeV with the $K$ or $\phi$ meson mass as additional input. The quoted errors represent statistical and systematic combined, the latter including those from continuum and chiral extrapolations, and from renormalization factors. Compared to quenched results, two flavors of dynamical quarks reduce quark masses by about 25%. Comment: 4 pages, revtex, 3 eps figures. Double statistics at beta=2.1, error estimates elaborated. Accepted for publication in Phys. Rev. Lett  [Show abstract] [Hide abstract]
ABSTRACT: We present updated results of the CPPACS calculation of the light hadron spectrum in Nf = 2 full QCD. Simulations are made with an RGimproved gauge action and a tadpoleimproved clover quark action for sea quark masses corresponding to mPS/mv ~ 0.80.6 and the lattice spacing a = 0.220.09 fm. A comparison of the Nf = 2 QCD spectrum with new quenched results, obtained with the same improved action, shows clearly the existence of sea quark effects in vector meson masses. Results for light quark masses are also presented 
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ABSTRACT: We present results of the light hadron spectrum derived from largescale simulations in lattice QCD on the CPPACS computer. The spectrum calculated in the quenched approximation systematically deviates from the experiment. We find indications that the discrepancy is significantly reduced by introduction of two flavors of light dynamical quarks. The strange quark mass in full QCD turns out to be ~ 85 MeV in the MS scheme at mu = 2 GeV, which is significantly smaller than previous phenomenological estimates.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the effects of action improvement on the light hadron spectrum and the static quark potential in twoflavor QCD for a1≈1 GeV and mPS/mV=0.7–0.9. We compare a renormalization group improved action with the plaquette action for gluons and the SWclover action with the Wilson action for quarks. We find a significant improvement in the hadron spectrum by improving the quark action, while the gluon improvement is crucial for a rotationally invariant static potential. We also explore the region of light quark masses corresponding to mPS/mV>~0.4 on a 2.7 fm lattice using the improved gauge and quark action. A flattening of the potential is not observed up to 2 fm. 
Article: Quenched Light Hadron Spectrum
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ABSTRACT: We present results of a largescale simulation for the flavor nonsinglet 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 $a \approx$ 0.1  0.05 fm on lattices with a physical extent of 3 fm at five quark masses corresponding to $m_\pi/m_\rho \approx 0.75$  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.  [Show abstract] [Hide abstract]
ABSTRACT: We report on an ongoing twoflavor full QCD study on CPPACS using an RGimproved gauge action and a tadpoleimproved SW quark action. Runs are made for three lattice spacings a−1 ≈ 0.9, 1.3, and 2.5 GeV on 123 × 24, 163 × 32, and 243 × 48 lattices. Four sea quark masses having mPS/mV ≈ 0.80.6 are simulated, for each of which hadron masses are evaluated for valence quark masses corresponding to mPS/mV ≈ 0.80.5. Results for hadron and light quark masses are presented and compared with those obtained in quenched QCD.  [Show abstract] [Hide abstract]
ABSTRACT: We report results on the static quark potential in twoflavor full QCD. The calculation is performed for three values of lattice spacing a−1 ≈ 0.9, 1.3 and 2.5 GeV on 123 × 24, 163 × 32 and 243 × 48 lattices respectively, at sea quark masses corresponding to mπ/mρ ≈ 0.80.6. An RGimproved gauge action and a tadpoleimproved SW clover quark action are employed. We discuss scaling of and effects of dynamical quarks on the potential.  [Show abstract] [Hide abstract]
ABSTRACT: We report the final results of the CPPACS calculation for the quenched light hadron spectrum with the Wilson quark action. Our data support the presence of quenched chiral singularities, and this motivates us to use mass formulae based on quenched chiral perturbation theory in order to extrapolate hadron masses to the physical point. Hadron masses and decay constants in the continuum limit show unambiguous systematic deviations from experiment. We also report the results for light quark masses. Comment: LATTICE98(spectrum). The poster at Lattice98 can be obtained from http://www.rccp.tsukuba.ac.jp/people/yoshie/Lat98.Poster/  [Show abstract] [Hide abstract]
ABSTRACT: We present progress report of a CPPACS calculation of quenched QCD spectrum with the Wilson quark action. Light hadron masses and meson decay constants are obtained at β =5.9, 6.1, and 6.25 on lattices with a physical extent of 3 fm, and for the range of quark mass corresponding to mπ/mp ≈ 0.75 – 0.4. Nucleon mass at each β appears to be a convex function of quark mass, and consequently the value at the physical quark mass is much smaller than previously thought. Hadron masses extrapolated to the continuum limit exhibits a significant deviation from experimental values: with K meson mass to fix strange quark mass, strange meson and baryon masses are systematically lower. Light quark masses determined from the axial Ward identity are shown to agree with those from perturbation theory in the continuum limit. Decay constants of mesons are also discussed. 
Article: Topology in QCD
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ABSTRACT: Topology on the lattice is reviewed. In quenched QCD topological susceptibility chi is fully understood. The WittenVeneziano mechanism for the eta' mass is confirmed. The topological susceptibility drops to zero at the deconfining phase transition. Preliminary results are also presented for chi and chi' in full QCD, and for the spin content of the proton. The only problem there is the difficulty of the usual Hybrid Monte Carlo algorithm to bring topology to equilibrium.  [Show abstract] [Hide abstract]
ABSTRACT: Parallel tempering simulates at many quark masses simultaneously, by changing the mass during the simulation while remaining in equilibrium. The algorithm is faster than pure HMC if more than one mass is needed, and works better the smaller the smallest mass is. Comment: 4 pages, 2 figures, Combined proceedings for Lattice 97, Edinburgh and the International Workshop 'Lattice QCD on Parallel Computers', University of Tsukuba, Japan  [Show abstract] [Hide abstract]
ABSTRACT: We present first results from a full QCD calculation on the CPPACS, comparing various actions at $a^{1} \sim 1 GeV$ and $m_\pi/m_\rho \approx 0.7$0.9. We use the plaquette and a renormalization group improved action for the gluons, and the Wilson and the SWClover action for quarks. We find that significant improvements in the hadron spectrum results from improving the quarks, while the gluon improvement is required for a rotationally invariant static potential. An ongoing effort towards exploring the chiral limit in full QCD is described. Comment: 6 pages, based on talks presented by R. Burkhalter and T. Kaneko at Lattice97, Edinburgh  [Show abstract] [Hide abstract]
ABSTRACT: The quenched hadron spectrum in the continuum obtained with the Wilson quark action in recent simulations on the CPPACS is presented. Results for the light quark masses and the QCD scale parameter are reported. Comment: Talk presented by K. Kanaya at Lattice97, Edinburgh
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1k  Citations  
67.67  Total Impact Points  
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19972003

University of Tsukuba
 Centre for Computational Sciences
Tsukuba, Ibarakiken, Japan
