著者

Tsutsui N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.11, pp.111501, 2004-12

被引用文献数

24 15

---

We present a quenched lattice QCD calculation of the alpha and beta parameters of the proton decay matrix element. The simulation is carried out using the Wilson quark action at three values of the lattice spacing in the range a[approximate]0.1-0.064 fm to study the scaling violation effect. We find only mild scaling violation when the lattice scale is determined by the nucleon mass. We obtain in the continuum limit,

著者

Yoshimi K Kaneko T Voigt B Mashimo T

出版者

Nature Publishing Group

雑誌

Nature communications (ISSN:20411723)

巻号頁・発行日

vol.5, 2014-06-26

被引用文献数

152

---

CRISPR/Casシステムを用いたアレル特異的ゲノム編集とラット毛色突然変異の修復!.京都大学プレスリリース. 2014-06-27.

著者

Ohki H. Takeda K. Aoki S. Hashimoto S. Kaneko T. Matsufuru H. Noaki J. Onogi T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.87, no.3, pp.034509, 2013-02

被引用文献数

61

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We calculate the strange quark content of the nucleon ⟨N

著者

Aoki S. Fukugita M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Ukawa A. Yamazaki T. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.9, pp.094504, 2005-05

被引用文献数

68

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We calculate the two-pion wave function in the ground state of the I=2 S-wave system and find the interaction range between two pions, which allows us to examine the validity of the necessary condition for the finite-volume method for the scattering length proposed by Lüscher. We work in the quenched approximation employing a renormalization group improved gauge action for gluons and an improved Wilson action for quarks at 1/a=1.207(12) GeV on 163×80, 203×80, and 243×80 lattices. We conclude that the necessary condition is satisfied within the statistical errors for the lattice sizes L>=24 (3.92 fm) when the quark mass is in the range that corresponds to mpi2=0.273–0.736 GeV2. We obtain the scattering length with a smaller statistical error from the wave function than from the two-pion time correlator.

著者

Yamada N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Tsutsui N. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.5, pp.054505, 2005-03

被引用文献数

16 19

---

We perform a nonperturbative determination of the O(a)-improvement coefficient cSW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0–5.2 on a single lattice size of 83×16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for cSW and the critical hopping parameter Kc as a function of the bare coupling. This enables us to remove the O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for cSW suggests that finite volume effects in cSW are not large on the 83×16 lattice. We investigate Nf dependence of cSW by additional simulations for Nf=4, 2, and 0 at beta=9.6. As a preparatory step for this study, we also determine cSW in two-flavor QCD at beta=5.2. At this beta, several groups have carried out large-scale calculations of the hadron spectrum, while no systematic determination of cSW has been performed.

著者

Yamada N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Tsutsui N. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.5, pp.054505, 2005-03

被引用文献数

16 19

---

We perform a nonperturbative determination of the O(a)-improvement coefficient cSW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0–5.2 on a single lattice size of 83×16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for cSW and the critical hopping parameter Kc as a function of the bare coupling. This enables us to remove the O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for cSW suggests that finite volume effects in cSW are not large on the 83×16 lattice. We investigate Nf dependence of cSW by additional simulations for Nf=4, 2, and 0 at beta=9.6. As a preparatory step for this study, we also determine cSW in two-flavor QCD at beta=5.2. At this beta, several groups have carried out large-scale calculations of the hadron spectrum, while no systematic determination of cSW has been performed.

著者

Namekawa Y. Aoki S. Fukugita M. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. I. Okawa M. Ukawa A. Umeda T. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074503, 2004-10

被引用文献数

24 31

---

We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to mPS/mV=0.60–0.35. Numerical simulations are carried out using the RG-improved gauge action and the meanfield-improved clover quark action at beta=1.8 (a=0.2 fm from rho meson mass). We observe that the light hadron spectrum for small sea quark mass does not follow the expectation from chiral extrapolations with quadratic functions made from the region of mPS/mV=0.80–0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fail, the Wilson ChPT (WChPT) that includes a2 effects associated with explicit chiral symmetry breaking successfully fits the whole data: In particular, WChPT correctly predicts the light quark mass spectrum from simulations for medium heavy quark mass, such as mPS/mV>~0.5. Reanalyzing the previous data with the use of WChPT, we find the mean up and down quark mass being smaller than the previous result from quadratic chiral extrapolation by approximately 10%, mudMS-bar(µ=2 GeV)=3.11(17) [MeV] in the continuum limit.

著者

Yamazaki T. Aoki S. Fukugit M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074513, 2004-10

被引用文献数

82 94

---

We present a lattice QCD calculation of phase shift including the chiral and continuum extrapolations in two-flavor QCD. The calculation is carried out for I=2 S-wave pipi scattering. The phase shift is evaluated for two momentum systems, the center of mass and laboratory systems, by using the finite-volume method proposed by Lüscher in the center of mass system and its extension to general systems by Rummukainen and Gottlieb. The measurements are made at three different bare couplings beta=1.80, 1.95 and 2.10 using a renormalization group improved gauge and a tadpole improved clover fermion action, and employing a set of configurations generated for hadron spectroscopy in our previous work. The illustrative values we obtain for the phase shift in the continuum limit are delta(deg.)=-3.50(64), -9.5(30) and -16.9(64) for sqrt(s)(GeV)=0.4, 0.6 and 0.8, which are consistent with experiments.

著者

Takeda S. Aoki S. Fukugita M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074510, 2004-10

被引用文献数

16 23

---

We study the scaling behavior of the step scaling function for SU(3) gauge theory, employing the renormalization-group improved Iwasaki gauge action and the perturbatively improved Lüscher-Weisz gauge action. We confirm that the step scaling functions from the improved gauge actions agree with that previously obtained from the plaquette action within errors in the continuum limit at both weak and strong coupling regions. We also investigate how different choices of boundary counterterms for the improved gauge actions affect the scaling behavior. In the extrapolation to the continuum limit, we observe that the cutoff dependence becomes moderate for the Iwasaki action, if a perturbative reduction of scaling violations is applied to the simulation results. We also measure the low energy scale ratio with the Iwasaki action and confirm its universality.

著者

Aoki S. Fukugita M. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.3, pp.034503, 2004-08

被引用文献数

4

---

We report on a nonperturbative evaluation of the renormalization factors for the vector and axial-vector currents, ZV and ZA, in the quenched domain-wall QCD (DWQCD) with plaquette and renormalization-group-improved gauge actions. We take the Dirichlet boundary condition for both gauge and domain-wall fermion fields on the finite box, and introduce flavor-chiral Ward-Takahashi identities to calculate the renormalization factors. As a test of the method, we numerically confirm the expected relation that ZV~=ZA in DWQCD. Employing two different box sizes for the numerical simulations at several values of the gauge coupling constant g2 and the domain-wall height M, we extrapolate ZV to infinite volume to remove a/L errors. We finally give the interpolation formula of ZV in the infinite volume as a function of g2 and M.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.69, no.9, pp.094512, 2004-05

被引用文献数

5

---

We present a lattice QCD calculation of the heavy quark expansion parameters µpi2 and µG2 for heavy-light mesons and heavy-light-light baryons. The calculation is carried out on a 203×48 lattice at beta=6.0 in the quenched approximation, using the lattice NRQCD action for heavy quarks. We obtain the parameters µpi2 and µG2 in two different methods: a direct calculation of the matrix elements and an indirect calculation through the mass spectrum, and confirm that both the methods give consistent results. We also discuss an application to the lifetime ratios.

著者

Aoki S. Burkhalter R. Fukugita M. Hashimoto S. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.68, no.5, pp.054502, 2003-09

被引用文献数

98 238

---

We present a high statistics study of the light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Numerical simulations are carried out using the plaquette gauge action and the O(a)-improved Wilson quark action at β=5.2, where the lattice spacing is found to be a=0.0887(11) fm from the ρ meson mass, on a 203×48 lattice. At each of five sea quark masses corresponding to mPS/mV≃0.8–0.6, we generate 12 000 trajectories using a symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 123×48, 163×48 lattices. We also perform a set of simulations in quenched QCD with the same lattice actions at a similar lattice spacing to those for the full QCD runs. In the meson sector we find clear evidence of sea quark effects. The J parameter increases for lighter sea quark masses, and the full QCD meson masses are systematically closer to experiment than in quenched QCD. Careful finite-size studies are made to ascertain that these are not due to finite-size effects. Evidence of sea quark effects is less clear in the baryon sector due to larger finite-size effects. We also calculate light quark masses and find mudMS̅ (2 GeV)=3.223(-0.069+0.046) MeV and msMS̅ (2 GeV)=84.5(-1.7+12.0) MeV which are about 20% smaller than in quenched QCD.

著者

Noaki J. Aoki S. Aoki Y. Burkhalter R. Ejiri S. Fukugita M. Hashimoto S. Ishizuka N. Iwasaki Y. Izubuchi T. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. Nagai K. I. Okawa M. Taniguch Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.68, no.1, pp.014501, 2003-07

被引用文献数

45 146

---

We explore the application of the domain wall fermion formalism of lattice QCD to calculate the K→ππ decay amplitudes in terms of the K+→π+ and K0→0 hadronic matrix elements through relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD using the domain-wall fermion action for quarks and a renormalization group-improved gauge action for gluons on a 163×32×16 and 243×32×16 lattice at β=2.6 corresponding to the lattice spacing 1/a≈2 GeV. Quark loop contractions which appear in Penguin diagrams are calculated by the random noise method, and the ΔI=1/2 matrix elements which require subtractions with the quark loop contractions are obtained with a statistical accuracy of about 10%. We investigate the chiral properties required of the K+→π+ matrix elements. Matching the lattice matrix elements to those in the continuum at μ=1/a using the perturbative renormalization factor to one loop order, and running to the scale μ=mc=1.3 GeV with the renormalization group for Nf=3 flavors, we calculate all the matrix elements needed for the decay amplitudes. With these matrix elements, the ΔI=3/2 decay amplitude Re A2 shows a good agreement with experiment after an extrapolation to the chiral limit. The ΔI=1/2 amplitude Re A0, on the other hand, is about 50–60 % of the experimental one even after chiral extrapolation. In view of the insufficient enhancement of the ΔI=1/2 contribution, we employ the experimental values for the real parts of the decay amplitudes in our calculation of ɛ′/ɛ. The central values of our result indicate that the ΔI=3/2 contribution is larger than the ΔI=1/2 contribution so that ɛ′/ɛ is negative and has a magnitude of order 10-4. We discuss in detail possible systematic uncertainties, which seem too large for a definite conclusion on the value of ɛ′/ɛ.

著者

Aoki S. Boyd G. Burkhalter R. Ejiri S. Fukugita M. Hashimoto S. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Nagai K. Okawa M. Shanahan H. P. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.67, no.3, pp.034503, 2003-02

被引用文献数

75

---

We present the details of simulations for the light hadron spectrum in quenched QCD carried out on the CP-PACS 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≈0.1–0.05 fm and spatial extent Lsa≈3 fm. 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 axial-vector Ward identity. The two results converge toward the continuum limit, yielding mud=4.29(14)-0.79+0.51 MeV 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+5.8 MeV from mK and ms=142.3(5.8)-0+22.0 MeV 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.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.67, no.1, pp.014506, 2003-01

被引用文献数

14 49

---

We present our results of lattice calculations of B parameters, which parametrize ΔB=2 transition amplitudes together with the leptonic decay constant. Calculations are made in the quenched approximation at β=5.7, 5.9, 6.0 and 6.1, using NRQCD action for heavy quarks and the O(a)-improved Wilson action for light quarks. The operators are perturbatively renormalized including the correction of O(αs/(aM)m) (m>~0). We examine the scaling behavior of B parameters, and discuss the systematic uncertainties based on the results with several different truncations of higher order terms in 1/M and αs expansions. We find BBd(mb)=0.84(3)(5), BBs/BBd=1.020(21)(-16+15)(-0+5) and BSs(mb)=0.85(1)(5)(-0+1) in the quenched approximation. The errors represent statistical and systematic errors as well as the uncertainty in the determination of strange quark mass.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.67, no.1, pp.014502, 2003-01

被引用文献数

38 61

---

We present a lattice QCD calculation of the scattering phase shift for the I=2 S-wave two-pion system using the finite size method proposed by Lüscher. We work in the quenched approximation employing the standard plaquette action at β=5.9 for gluons and the Wilson fermion action for quarks. The phase shift is extracted from the energy eigenvalues of the two-pion system, which are obtained by a diagonalization of the pion four-point function evaluated for a set of relative spatial momenta. In order to change the momentum of the two-pion system, calculations are carried out on 243×60, 323×60, and 483×60 lattices. The phase shift is successfully calculated over the momentum range 0<p2<0.3 GeV2.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tominaga S. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.66, no.7, pp.077501, 2002-10

被引用文献数

34 52

---

The calculation of the I=2 pion scattering length in quenched lattice QCD is reexamined. The calculation is carried out with the Wilson fermion action employing Lüscher’s finite size scaling method at β=5.9, 6.1, and 6.3 corresponding to the range of lattice spacing a≃0.12-0.07 fm. We obtain in the continuum limit a0/mπ=-2.09(35) 1/GeV2, which is consistent with the prediction of chiral perturbation theory a0/mπ=-2.265(51)1/GeV2.

著者

Aoki S. Burkhalter R. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tominaga S. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.65, no.9, pp.094507, 2002-04

被引用文献数

28 69

---

We present a polynomial hybrid Monte Carlo (PHMC) algorithm for lattice QCD with odd numbers of flavors of O(a)-improved Wilson quark action. The algorithm makes use of the non-Hermitian Chebyshev polynomial to approximate the inverse square root of the fermion matrix required for an odd number of flavors. The systematic error from the polynomial approximation is removed by a noisy Metropolis test for which a new method is developed. Investigating the property of our PHMC algorithm in the Nf=2 QCD case, we find that it is as efficient as the conventional HMC algorithm for a moderately large lattice size (163×48) with intermediate quark masses (mPS/mV∼0.7–0.8). We test our odd-flavor algorithm through extensive simulations of two-flavor QCD treated as an Nf=1+1 system, and comparing the results with those of the established algorithms for Nf=2 QCD. These tests establish that our PHMC algorithm works on a moderately large lattice size with intermediate quark masses (163×48,mPS/mV∼0.7–0.8). Finally we experiment with the (2+1)-flavor QCD simulation on small lattices (43×8 and 83×16), and confirm the agreement of our results with those obtained with the R algorithm and extrapolated to a zero molecular dynamics step size.

著者

Okamoto M. Aoki S. Burkhalter R. Ejiri S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. Nagai K. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.65, no.9, pp.094508, 2002-04

被引用文献数

91 128

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We present a detailed study of the charmonium spectrum using anisotropic lattice QCD. We first derive a tree-level improved clover quark action on the anisotropic lattice for arbitrary quark mass by matching the Hamiltonian on the lattice and in the continuum. The heavy quark mass dependence of the improvement coefficients, i.e., the ratio of the hopping parameters ζ=Kt/Ks and the clover coefficients cs,t, is examined at the tree level, and effects of the choice of the spatial Wilson parameter rs are discussed. We then compute the charmonium spectrum in the quenched approximation employing ξ=as/at=3 anisotropic lattices. Simulations are made with the standard anisotropic gauge action and the anisotropic clover quark action with rs=1 at four lattice spacings in the range as=0.07–0.2 fm. The clover coefficients cs,t are estimated from tree-level tadpole improvement. On the other hand, for the ratio of the hopping parameters ζ, we adopt both the tree-level tadpole-improved value and a non-perturbative one. The latter employs the condition that the speed of light calculated from the meson energy-momentum relation be unity. We calculate the spectrum of S and P states and their excitations using both the pole and kinetic masses. We find that the combination of the pole mass and the tadpole-improved value of ζ to yield the smoothest approach to the continuum limit, which we then adopt for the continuum extrapolation of the spectrum. The results largely depend on the scale input even in the continuum limit, showing a quenching effect. When the lattice spacing is determined from the 1P-1S splitting, the deviation from the experimental value is estimated to be ∼30% for the S-state hyperfine splitting and ∼20% for the P-state fine structure. Our results are consistent with previous results at ξ=2 obtained by Chen when the lattice spacing is determined from the Sommer scale r0. We also address the problem with the hyperfine splitting that different choices of the clover coefficients lead to disagreeing results in the continuum limit. Making a leading order analysis based on potential models we show that a large hyperfine splitting ∼95 MeV obtained by Klassen with a different choice of the clover coefficients is likely an overestimate.

著者

Khan A. Ali Aoki S. Boyd G. Burkhalter R. Ejiri S. Fukugita M. Hashimoto S. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Manke T. Nagai K. Okawa M. Shanahan H. P. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.65, no.5, pp.054505, 2002-02

被引用文献数

195 138

---

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 in dynamical up and down quark masses. Gauge configurations are generated with a renormalization-group improved gauge action and a mean field improved clover quark action at three values of β=6/g2, corresponding to lattice spacings of a≈0.22, 0.16 and 0.11 fm, and four sea quark masses corresponding to mPS/mV≈0.8, 0.75, 0.7 and 0.6. The sizes of lattice are chosen to be 123×24, 163×32 and 243×48 so that the physical spatial size is kept constant at La≈2.5 fm. Hadron masses, light quark masses and meson decay constants are measured at five valence quark masses corresponding to mPS/mV≈0.8, 0.75, 0.7, 0.6 and 0.5. 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, quantitatively confirming the systematic deviation of the quenched spectrum from experiment. We find the two-flavor full QCD meson masses in the continuum limit to be much closer to experimental meson masses than those from quenched QCD. When using the K meson mass to fix the strange quark mass, the difference between quenched QCD and experiment of 2.6-0.9+0.3% for the K* meson mass and of 4.1-1.6+0.5% for the φ meson mass is reduced to 0.7-1.7+1.1% and 1.3-2.5+1.8% in full QCD, where the errors include estimates of systematic errors of the continuum extrapolation as well as statistical errors. Analyses of the J parameter yield a similar trend in that the quenched estimate in the continuum limit J=0.375-0.009+0.039 increases to J=0.440-0.031+0.061 in two-flavor full QCD, approaching the experimental value J≈0.48. We take these results as manifestations of sea quark effects in two-flavor full QCD. For baryon masses full QCD values for strange baryons such as Ξ and Ω are in agreement with experiment, while they differ increasingly with decreasing strange quark content, resulting in a nucleon mass higher than experiment by 10% and a Δ mass by 13%. The pattern suggests finite size effects as a possible origin for this deviation. For light quark masses in the continuum limit we obtain mudMS̅ (2 GeV)=3.44-0.22+0.14 MeV and msMS̅ (2 GeV)=88-6+4 MeV (K-input) and msMS̅ (2 GeV)=90-11+5 MeV (φ-input), 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. The need for a nonperturbative estimate of renormalization factors is discussed.