Publications (238)448.89 Total impact

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 updatedPhysical Review D 02/2010; 82(7). DOI:10.1103/PhysRevD.82.074505 · 4.64 Impact Factor  [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.Physical review D: Particles and fields 01/2010; 81(3). DOI:10.1103/PhysRevD.81.034502 · 4.86 Impact Factor 
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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 correctedPhysical review D: Particles and fields 05/2009; 80(3). DOI:10.1103/PhysRevD.80.034508 · 4.86 Impact Factor 

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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.Physical Review Letters 01/2009; 101(24):242001. DOI:10.1103/PhysRevLett.101.242001 · 7.51 Impact Factor  [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.Physical Review Letters 12/2008; 101(20):202004. DOI:10.1103/PHYSREVLETT.101.202004 · 7.51 Impact Factor  [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  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the pion vector and scalar form factors in twoflavor QCD. Gauge configurations are generated with dynamical overlap quarks on a 16^3 x 32 lattice at a lattice spacing of 0.12 fm with sea quark masses down to a sixth of the physical strange quark mass. Contributions of disconnected diagrams to the scalar form factor is calculated employing the alltoall quark propagators. We present a detailed comparison of the vector and scalar radii with chiral perturbation theory to two loops. Comment: 7 pages; Talk presented at the XXVI International Symposium on Lattice Field Theory, July 14  19 2008, Williamsburg, Virginia, USA; v2: a reference added  [Show abstract] [Hide abstract]
ABSTRACT: We report on a numerical simulation with 2+1 dynamical flavors of overlap fermions. We calculate pseudoscalar masses and decay constants on a $16^3\times 48 \times (0.11 {\rm fm})^4$ lattice at five different up and down quark masses and two strange quark masses. The lightest pion mass corresponds to $\approx 310$ MeV. We also study the validity of the chiral perturbation theory using the results of the numerical simulation with two dynamical flavors and conclude that the oneloop formulae cannot be directly applied in the strange quark mass region. We therefore extrapolate our 2+1flavor results to the chiral limit by fitting the data to the twoloop formulae of the chiral perturbation theory. Comment: 7 pages, 7 figure files. Talk given at the XXVI International Symposium on Lattice Field Theory, July 14  19 2008, Williamsburg, Virginia, USA  [Show abstract] [Hide abstract]
ABSTRACT: We determine the topological susceptibility \chi_t in the topologicallytrivial sector generated by lattice simulations of N_f = 2+1 QCD with overlap Dirac fermion, on a 16^3 x 48 lattice with lattice spacing ~ 0.11 fm, for five sea quark masses m_q ranging from m_s/6 to m_s (where m_s is the physical strange quark mass). The \chi_t is extracted from the plateau (at large time separation) of the 2point and 4point timecorrelation functions of the flavorsinglet pseudoscalar meson \eta', which arises from the finite size effect due to fixed topology. In the small m_q regime, our result of \chi_t agrees with the chiral effective theory. Using the formula \chi_t = \Sigma(m_u^{1} + m_d^{1} + m_s^{1})^{1} by LeutwylerSmilga, we obtain the chiral condensate \Sigma^{MSbar}(2 GeV) = [249(4)(2) MeV]^3. Comment: 7 pages, 3 figures, talk presented at the XXVI International Symposium on Lattice Field Theory, July 1419, 2008, Williamsburg, Virginia, USA  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the nucleon sigma term in twoflavor lattice QCD utilizing the FeynmanHellman theorem. Both sea and valence quarks are described by the overlap fermion formulation, which preserves exact chiral and flavor symmetries on the lattice. We analyse the lattice data for the nucleon mass using the analytical formulae derived from the baryon chiral perturbation theory. From the data at valence quark mass set different from sea quark mass, we may extract the sea quark contribution to the sigma term, which corresponds to the strange quark content. We find that the strange quark content is much smaller than the previous lattice calculations and phenomenological estimates.Physical review D: Particles and fields 07/2008; 78(5). DOI:10.1103/PhysRevD.78.054502 · 4.86 Impact Factor 
Article: Lattice study of vacuum polarization function and determination of strong coupling constant
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ABSTRACT: We calculate the vacuum polarization functions on the lattice using the overlap fermion formulation.By matching the lattice data at large momentum scales with the perturbative expansion supplemented by Operator Product Expansion (OPE), we extract the strong coupling constant $\alpha_s(\mu)$ in twoflavor QCD as $\Lambda^{(2)}_{\overline{MS}}$ = $0.234(9)(^{+16}_{ 0})$ GeV, where the errors are statistical and systematic, respectively. In addition, from the analysis of the difference between the vector and axialvector channels, we obtain some of the fourquark condensates. Comment: 24 pages, 9 figures, enlarged version published in Phys. Rev. DPhysical review D: Particles and fields 07/2008; 79(7). DOI:10.1103/PhysRevD.79.074510 · 4.86 Impact Factor
Publication Stats
5k  Citations  
448.89  Total Impact Points  
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Institutions

2009–2014

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


2–2014

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


2000–2002

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


1999

Fermi National Accelerator Laboratory (Fermilab)
 Theoretical Physics Department
Batavia, Illinois, United States


1996

University of Yamanashi
 Faculty of Engineering
Kōhu, Yamanashi, Japan


1993

Hiroshima University
 Graduate School of Science
Hirosima, Hiroshima, Japan
