Publications (242)451.81 Total impact
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ABSTRACT: We calculate the strange quark content of the nucleon directly from its disconnected threepoint function in N_f=2+1 QCD. Chiral symmetry is crucial to avoid a possibly large contamination due to operator mixing, and is exactly preserved by employing the overlap quark action. We also use the alltoall quark propagator and the lowmode averaging technique in order to accurately calculate the relevant nucleon correlator. Our preliminary result extrapolated to the physical point is f_{T_s} = 0.013(12)(16). This is in good agreement with our previous estimate in N_f=2 QCD as well as those from our indirect calculations using the FeynmanHellmann theorem. Comment: 7pages, talk presented at The XXVIII International Symposium on Lattice Field Theory, Lattice2010  [Show abstract] [Hide abstract]
ABSTRACT: We report on our calculation of pion and kaon form factors in threeflavor QCD using the overlap quark action. Gauge ensembles are generated on a 16^3 \times 48 lattice at a lattice spacing of 0.11 fm with pion masses down to 310 MeV. Connected and disconnected meson correaltors are calculated using the alltoall quark propagator. We present our preliminary analysis on the chiral behavior of the electromagnetic and scalar form factors as well as a comparison of the shape of the K to pi form factors with experiment. Comment: 7pages, talk presented at The XXVIII International Symposium on Lattice Field Theory, Lattice2010  [Show abstract] [Hide abstract]
ABSTRACT: Strange quark content of the nucleon is calculated in dynamical lattice QCD employing the overlap fermion formulation. For this quantity, exact chiral symmetry guaranteed by the GinspargWilson relation is crucial to avoid large contamination due to a possible operator mixing with $\bar{u}u+\bar{d}d$. Gauge configurations are generated with two dynamical flavors on a 16^3 x 32 lattice at a lattice spacing a \simeq 0.12fm. We directly calculate the relevant threepoint function on the lattice including a disconnected strange quark loop utilizing the techniques of alltoall quark propagator and lowmode averaging. Our result f_{T_s} = 0.032(8)(22), is in good agreement with our previous indirect estimate using the FeynmanHellmann theorem.  [Show abstract] [Hide abstract]
ABSTRACT: We perform a precise calculation of the chiral condensate in QCD using lattice QCD with 2+1 flavors of dynamical overlap quarks. Up and down quark masses cover a range between 3 and 100 MeV on a 16^3x48 lattice at a lattice spacing around 0.11 fm. At the lightest sea quark mass, the finite volume system on the lattice is in the epsilonregime. By matching the lowlying eigenvalue spectrum of the Dirac operator with the prediction of chiral perturbation theory at the nexttoleading order, we determine the chiral condensate in 2+1flavor QCD with strange quark mass fixed at its physical value as Sigma (MSbar at 2 GeV) = [242(04)(^+19_18}) MeV}]^3, where the errors are statistical and systematic, respectively. Comment: 4 pages, 3 figures, errors in table 1 and fig.3 corrected. Published in PRL  [Show abstract] [Hide abstract]
ABSTRACT: We perform a precise calculation of the chiral condensate in QCD using lattice QCD with 2+1 flavors of dynamical overlap quarks. Up and down quark masses cover a range between 3 and 100 MeV on a 16{3}x48 lattice at a lattice spacing approximately 0.11 fm. At the lightest sea quark mass, the finite volume system on the lattice is in the regime. By matching the lowlying eigenvalue spectrum of the Dirac operator with the prediction of chiral perturbation theory at the nexttoleading order, we determine the chiral condensate in (2+1)flavor QCD with strange quark mass fixed at its physical value as Sigma;{MS[over ]}(2 GeV)=[242(04)(+19/18) MeV]{3} where the errors are statistical and systematic, respectively. 
Article: Physics at Super B Factory
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ABSTRACT: This report presents the results of studies that investigate the physics reach at a Super $B$ factory, an asymmetricenergy $e^+e^$ collider with a design luminosity of $8 \times 10^{35}$ cm$^{2}$s$^{1}$, which is around 50 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented.  [Show abstract] [Hide abstract]
ABSTRACT: We determine the strong coupling constant $\alpha_s$ from a lattice calculation of vacuum polarization functions (VPF) in threeflavor QCD with dynamical overlap fermions. Fitting lattice data of VPF to the continuum perturbative formula including the operator product expansion, we extract the QCD scale parameter $\Lambda_{\overline{MS}}^{(3)}$. At the $Z$ boson mass scale, we obtain $\alpha_s^{(5)}(M_Z)=0.1181(3)(^{+14}_{12})$, where the first error is statistical and the second is our estimate of various systematic uncertainties. Comment: 15 pages, 7 figures, references updated  [Show abstract] [Hide abstract]
ABSTRACT: Using the nonperturbative renormalization technique, we calculate the renormalization factors for quark bilinear operators made of overlap fermions on the lattice. The background gauge field is generated by the JLQCD and TWQCD Collaborations, including dynamical effects of two or 2+1 flavors of light quarks on a 163×32 or 163×48 lattice at lattice spacing around 0.1 fm. By reducing the quark mass close to the chiral limit, where the finite volume system enters the socalled ϵ regime, the unwanted effect of spontaneous chiral symmetry breaking on the renormalization factors is suppressed. On the lattices in the conventional p regime, this effect is precisely subtracted by separately calculating the contributions from the chiral condensate. 

Article: 0 to twophoton decay in lattice QCD
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ABSTRACT: We calculate the neutral pion ($\pi^0$) to offshell two photon ($\gamma^*\gamma^*$) transition form factor in lattice QCD. The transition form factor can be extracted from the threepoint function of the form (axialvector)(vector)(vector) as a function of offshell twophoton momentum. Since the axialanomaly plays an important role in the $\pi^0\to\gamma\gamma$ decay process, we employ the overlap fermion, which preserves the exact chiral symmetery on the lattice. After extrapolating to the chiral and the vanishing photon momentum limit with a fit function based on vector meson dominance (VMD) model, we find that the AdlerBellJackiw anomaly is correctly reproduced. Comment: 7 pages. Talk presented at The XXVII International Symposium on Lattice Field Theory, July 2631 2009, Peking University, Beijing, China  [Show abstract] [Hide abstract]
ABSTRACT: We present an update of the light meson spectrum with $N_f$=2+1 overlap fermions on a $16^3\times 48$ lattice at five different up and down quark masses and two strange quark masses. Based on our experience with the previous simulation with $N_f=2$, we carry out the chiral extrapolation with the prediction of the chiral perturbation theory at the nexttonextto leading order. We also check the consistency of our analysis by using alternative chiral extrapolation with a reduced theory in which the strange quark mass is integrated out. Comment: 7 pages, 6 figures, talk presented at The XXVII International Symposium on Lattice Field Theory  LAT2009, July 2631 2009, Peking University, Beijing, China  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the nucleon strange quark content directly from disconnected threepoint functions. Numerical simulations are carried out in twoflavor QCD using the overlap quark action with up and down quark masses down to a fifth of the physical strange quark mass. To improve the statistical accuracy, we calculate the nucleon twopoint functions with the lowmode averaging technique, whereas the alltoall quark propagator is used for the disconnected quark loop. We obtain the y parameter, which is the ratio of the strange and light quark contents, y = 0.024(45) at the physical point. This is in a good agreement with our earlier calculation from the nucleon spectrum through the FeynmanHellmann theorem. Comment: 7 pages, talk presented at The XXVII International Symposium on Lattice Field Theory (Lattice2009), July 2631 2009, Peking University, Beijing, China  [Show abstract] [Hide abstract]
ABSTRACT: We report on our study of flavorsinglet mesons in threeflavor QCD with dynamical overlap quarks. Gauge ensembles are generated on a 16^3 x 48 lattice at a lattice spacing of 0.10 fm with the strange quark masses around its physical value m_s,phys and up and down quark masses down to m_s,phys/5. Connected and disconnected meson correlators are calculated using the alltoall quark propagator. We present our preliminary results on the spectrum of flavorsinglet pseudoscalar and vector mesons. Comment: 7 pages, talk presented at The XXVII International Symposium on Lattice Field Theory  LAT2009, July 2631 2009, Peking University, Beijing, China 
Article: Nucleon sigma term and strange quark content in 2+1flavor QCD with dynamical overlap fermions
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ABSTRACT: We study the sigma term and the strange quark content of nucleon in 2+1flavor QCD with dynamical overlap fermions. We analyze the lattice data of nucleon mass taken at two different strange quark masses with five values of up and down quark masses each. Using the reweighting technique, we study the strange quark mass dependence of the nucleon and extract the strange quark content. Comment: 7 pages, 4 figures, talk given at the XXVII International Symposium on Lattice Field Theory, July 2631 2009, Peking University, Beijing, China  [Show abstract] [Hide abstract]
ABSTRACT: We calculate pion vector and scalar form factors in twoflavor lattice QCD and study the chiral behavior of the vector and scalar radii <r^2>_{V,S}. Numerical simulations are carried out on a 16^3 x 32 lattice at a lattice spacing of 0.12 fm with quark masses down to \sim m_s/6, where m_s is the physical strange quark mass. Chiral symmetry, which is essential for a direct comparison with chiral perturbation theory (ChPT), is exactly preserved in our calculation at finite lattice spacing by employing the overlap quark action. We utilize the socalled alltoall quark propagator in order to calculate the scalar form factor including the contributions of disconnected diagrams and to improve statistical accuracy of the form factors. A detailed comparison with ChPT reveals that the nexttonexttoleadingorder contributions to the radii are essential to describe their chiral behavior in the region of quark mass from m_s/6 to m_s/2. Chiral extrapolation based on twoloop ChPT yields <r^2>_V=0.409(23)(37)fm and <r^2>_S=0.617(79)(66)fm, which are consistent with phenomenological analysis. We also present our estimates of relevant lowenergy constants. Comment: 32 pages, 18 figures, typos corrected 

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ABSTRACT: We present a lattice calculation of L10, one of the lowenergy constants in chiral perturbation theory, and the chargedneutral pion squaredmass splitting, using dynamical overlap fermion. The exact chiral symmetry of the overlap fermion allows us to reliably extract these quantities from the difference of the vacuum polarization functions for vector and axialvector currents. In the context of the technicolor models, these two quantities are read as the S parameter and the pseudo NambuGoldstone boson mass, respectively, and play an important role in discriminating the models from others. This calculation can serve as a feasibility study of the lattice techniques for more general technicolor gauge theories.  [Show abstract] [Hide abstract]
ABSTRACT: We test the convergence property of the chiral perturbation theory using a lattice QCD calculation of pion mass and decay constant with two dynamical quark flavors. The lattice calculation is performed using the overlap fermion formulation, which realizes exact chiral symmetry at finite lattice spacing. By comparing various expansion prescriptions, we find that the chiral expansion is well saturated at the nexttoleading order for pions lighter than approximately 450 MeV. Better convergence behavior is found, in particular, for a resummed expansion parameter xi, with which the lattice data in the pion mass region 290750 MeV can be fitted well with the nexttonexttoleading order formulas. We obtain the results in twoflavor QCD for the low energy constants l[over ]_{3} and l[over ]_{4} as well as the pion decay constant, the chiral condensate, and the average up and down quark mass.  [Show abstract] [Hide abstract]
ABSTRACT: We present a calculation of the nucleon sigma term on twoflavor QCD configurations with dynamical overlap fermions. We analyse the lattice data for the nucleon mass using the baryon chiral perturbation theory. Using partially quenched data sets, we extract the connected and disconnected contributions to the nucleon sigma term separately. Chiral symmetry on the lattice simplifies the determination of the disconnected contribution. We find that the strange quark content, which determines the neutralino dark matter reaction rate with nucleon through the Higgs boson exchange, is much smaller than the previous lattice results. Comment: 7 pages, 6 figures, Talk given at 26th International Symposium on Lattice Field Theory (Lattice 2008), Williamsburg, Virginia, 1420 Jul 2008
Publication Stats
5k  Citations  
451.81  Total Impact Points  
Top Journals
Institutions

22015

High Energy Accelerator Research Organization
 • Institute of Particle and Nuclear Studies
 • Computing Research Center
Tsukuba, Ibaraki, Japan


20092014

The Graduate University for Advanced Studies
 School of High Energy Accelerator Science
Миура, Kanagawa, Japan


19992001

University of Tsukuba
 Centre for Computational Sciences
Tsukuba, Ibarakiken, Japan 
Fermi National Accelerator Laboratory (Fermilab)
 Theoretical Physics Department
Batavia, Illinois, United States


1998

The University of Tokyo
Tōkyō, Japan


1996

University of Yamanashi
 Faculty of Engineering
Kōhu, Yamanashi, Japan


1993

Hiroshima University
 Graduate School of Science
Hirosima, Hiroshima, Japan
