arXiv subjects

S. Aoki

Publications and source records attributed to S. Aoki.

At least 235 records · Page 13Linked to original sources

arXiv2007

Nuclear Force from Lattice QCD

Nucleon-nucleon (NN) potential is studied by lattice QCD simulations in the quenched approximation, using the plaquette gauge action and the Wilson quark action on a 32^4 (\simeq (4.4 fm)^4) lattice. A NN potential V_{NN}(r) is defined from the equal-time Bethe-Salpeter amplitude with a local interpolating operator for the nucleon. By studying the NN interaction in the ^1S_0 and ^3S_1 channels, we show that the central part of V_{NN}(r) has a strong repulsive core of a few hundred MeV at short distances (r \alt 0.5 fm) surrounded by an attractive well at medium and long distances. These features are consistent with the known phenomenological features of the nuclear force.

nucl-th↗

arXiv2007

2+1 flavor light hadron spectrum and quark masses with the O(a) improved Wilson-clover quark formalism

We present a summary of results of the joint CP-PACS and JLQCD project toward a 2+1 flavor full QCD simulation with the O(a)-improved Wilson quark formalism and the Iwasaki gauge action. Configurations were generated during 2002-2005 at three lattice spacings, a~0.076, 0.100 and 0.122 fm, keeping the physical volume constant at (2.0fm)^3. Up and down quark masses are taken in the range m_{PS}/m_V~0.6-0.78. We have completed the analysis for the light meson spectrum and quark masses in the continuum limit using the full configuration set. The predicted meson masses reproduce experimental values in the continuum limit at a 1% level. The average up and down, and strange quark masses turn out to be m_{ud}^{\bar{MS}}(μ=2 GeV)=3.50(14)({}^{+26}_{-15}) MeV and m_s^{\bar{MS}}(μ=2 GeV)=91.8(3.9)({}^{+6.8}_{-4.1}) MeV. We discuss our future strategy toward definitive results on hadron spectroscopy with the Wilson-clover formalism.

hep-lat↗

arXiv2007

Measurements of total and partial charge-changing cross sections for 200-400 MeV/nucleon 12C in water and polycarbonate

We have studied charged nuclear fragments produced by 200 - 400 MeV/nucleon carbon ions, interacting with water and polycarbonate, using a newly developed emulsion detector. Total and partial charge-changing cross sections for the production of B, Be, and Li fragments were measured and compared with both previously published measurements, and model predictions. This study is of importance for validating and improving carbon ion therapy treatment planning systems, and for estimating the radiological risks for personnel on space missions, since carbon is a significant component of the Galactic Cosmic Rays.

nucl-ex↗

arXiv2007

Non-perturbative improvement of the axial current with three dynamical flavors and the Iwasaki gauge action

We perform a non-perturbative determination of the improvement coefficient c_A to remove O(a) discretization errors in the axial vector current in three-flavor lattice QCD with the Iwasaki gauge action and the standard O$(a)$-improved Wilson quark action. An improvement condition with a good sensitivity to c_A is imposed at constant physics. Combining our results with the perturbative expansion, c_A is now known rather precisely for 1/a \gtrsim 1.6 GeV.

hep-lat↗

arXiv2007

Neutron electric dipole moment with external electric field method in lattice QCD

We discuss a possibility that the Neutron Electric Dipole Moment (NEDM) can be calculated in lattice QCD simulations in the presence of the CP violating $θ$ term. In this paper we measure the energy difference between spin-up and spin-down states of the neutron in the presence of an uniform and static external electric field. We first test this method in quenched QCD with the RG improved gauge action on a $16^3\times 32$ lattice at $a^{-1}\simeq$ 2 GeV, employing two different lattice fermion formulations, the domain-wall fermion and the clover fermion for quarks, at relatively heavy quark mass $(m_{PS}/m_V \simeq 0.85)$. We obtain non-zero values of NEDM from calculations with both fermion formulations. We next consider some systematic uncertainties of our method for NEDM, using $24^3\times 32$ lattice at the same lattice spacing only with the clover fermion. We finally investigate the quark mass dependence of NEDM and observe a non-vanishing behavior of NEDM toward the chiral limit. We interpret this behavior as a manifestation of the pathology in the quenched approximation.

hep-lat↗

arXiv2007

Heavy-Quark Free Energy, Debye Mass, and Spatial String Tension at Finite Temperature in Two Flavor Lattice QCD with Wilson Quark Action

We study Polyakov loop correlations and spatial Wilson loop at finite Temperature in two-flavor QCD simulations with the RG-improved gluon action and the clover-improved Wilson quark action on a $ 16^3 \times 4$ lattice. From the line of constant physics at $m_{\rm PS}/m_{\rm V}=0.65$ and 0.80, we extract the heavy-quark free energies, the effective running coupling $g_{\rm eff}(T)$ and the Debye screening mass $m_D(T)$ for various color channels of heavy quark--quark and quark--anti-quark pairs above the critical temperature. The free energies are well approximated by the screened Coulomb form with the appropriate Casimir factors at high temperature. The magnitude and the temperature dependence of the Debye mass are compared to those of the next-to-leading order thermal perturbation theory and to a phenomenological formula in terms of $g_{\rm eff}(T)$. We make a comparison between our results with the Wilson quark action and the previous results with the staggered quark action. The spatial string tension is also studied in the high temperature phase and is compared to the next-to-next-leading order prediction in an effective theory with dimensional reduction.

hep-lat↗

arXiv2007

First Nonperturbative Test of a Relativistic Heavy Quark Action in Quenched Lattice QCD

We perform a numerical test of a relativistic heavy quark(RHQ) action, recently proposed by Tsukuba group, in quenched lattice QCD at $a\simeq 0.1$ fm. With the use of the improvement parameters previously determined at one-loop level for the RHQ action, we investigate a restoration of rotational symmetry for heavy-heavy and heavy-light meson systems around the charm quark mass. We focused on two quantities, the meson dispersion relation and the pseudo-scalar meson decay constants. It is shown that the RHQ action significantly reduces the discretization errors due to the charm quark mass. We also calculate the S-state hyperfine splittings for the charmonium and charmed-strange mesons and the $D_s$ meson decay constant. The remaining discretization errors in the physical quantities are discussed.

hep-lat↗

arXiv2007

Thermodynamics of two-flavor lattice QCD with an improved Wilson quark action at non-zero temperature and density

We report the current status of our systematic studies of the QCD thermodynamics by lattice QCD simulations with two flavors of improved Wilson quarks. We evaluate the critical temperature of two flavor QCD in the chiral limit at zero chemical potential and show the preliminary result. Also we discuss fluctuations at none-zero temperature and density by calculating the quark number and isospin susceptibilities and their derivatives with respect to chemical potential.

hep-lat↗

arXiv2007

Two-flavor lattice QCD simulation in the epsilon-regime with exact chiral symmetry

We perform lattice simulations of two-flavor QCD using Neuberger's overlap fermion, with which the exact chiral symmetry is realized at finite lattice spacings. The epsilon-regime is reached by decreasing the light quark mass down to 3 MeV on a 16^3 32 lattice with a lattice spacing \sim 0.11 fm. We find a good agreement of the low-lying Dirac eigenvalue spectrum with the analytical predictions of the chiral random matrix theory, which reduces to the chiral perturbation theory in the epsilon-regime. The chiral condensate is extracted as Σ(2 GeV) = (251(7)(11) MeV)^3, where the errors are statistical and an estimate of the higher order effects in the epsilon-expansion.

hep-lat↗

arXiv2006

Mobility edge and locality of the overlap-Dirac operator with and without dynamical overlap fermions

We perform a systematic study of low-lying eigenmodes of $H_w$ with various gauge actions to find the optimal choice for dynamical overlap fermion simulations, with which one may achieve lower numerical cost for HMC and better locality property of the overlap kernel. For this purpose, our study is made with emphasis on the distribution of low-lying eigenvalues and the mobility edge with and without dynamical overlap fermions.

hep-lat↗

arXiv2006

Kaon $B$-parameters for Generic $ΔS=2$ Four-Quark Operators in Quenched Domain Wall QCD

We present a study of $B$-parameters for generic $ΔS=2$ four-quark operators in domain wall QCD. Our calculation covers all the $B$-parameters required to study the neutral kaon mixing in the standard model (SM) and beyond it. We evaluate one-loop renormalization factors of the operators employing the plaquette and Iwasaki gauge actions. Numerical simulations are carried out in quenched QCD with both gauge actions on $16^3\times 32\times 16$ and $24^3\times 32\times 16$ at the lattice spacing $1/a\approx 2$GeV. We investigate the relative magnitudes of the non-SM $B$-parameters to the SM one, which are compared with the previous results obtained with the overlap and the clover quark actions.

hep-lat↗

arXiv2006

An application of the UV-filtering preconditioner to the Polynomial Hybrid Monte Carlo algorithm

We apply the UV-filtering preconditioner, previously used to improve the Multi-Boson algorithm, to the Polynomial Hybrid Monte Carlo (UV-PHMC) algorithm. The performance test for the algorithm is given for the plaquette gauge action and the $O(a)$-improved Wilson action at $β=5.2, c_{\mathrm{sw}}=2.02, M_π/M_ρ\sim 0.8$ and 0.7 on a $16^3\times 48$ lattice. We find that the UV-filtering reduces the magnitude of the molecular dynamics force from the pseudo fermion by a factor 3 by tuning the UV-filter parameter. Combining with the multi-time scale molecular dynamics integrator we achieve a factor 2 improvement.

hep-lat↗

arXiv2006

2+1 Flavor Lattice QCD with Luescher's Domain-Decomposed HMC Algorithm

We report on a study of 2+1 flavor lattice QCD with the $O(a)$-improved Wilson quarks on a $16^3\times 32$ lattice at the lattice spacing $1/a\approx 2$GeV employing Luescher's domain-decomposed HMC(LDDHMC) algorithm. This is dedicated to a preliminary study for the PACS-CS project which plans to complete the Wilson-clover $N_f=2+1$ program lowering the up-down quark masses close to the physical values as much as possible. We focus on three issues: (i) how light quark masses we can reach with LDDHMC, (ii) efficiency of the algorithm compared with the conventional HMC, (iii) parameter choice for the production runs on PACS-CS.

hep-lat↗

arXiv2006

JLQCD's dynamical overlap project

We present an overview of our project of large-scale simulations with dynamical overlap fermions. The first production run in two-flavor QCD is on-going using the Iwasaki gauge action on a 16^3 \times 32 lattice at the lattice spacing of 0.12fm with six sea quark masses down to m_{s,phys}/6, where m_{s,phys} is the physical strange quark mass. We briefly introduce our choice of the lattice action and simulation algorithm, and describe the present status of the production run. Preliminary results on the light meson masses and the static quark potential are also reported.

hep-lat↗

arXiv2006

Finite temperature phase transition of two-flavor QCD with an improved Wilson quark action

We study the phase structure of QCD at finite temperatures with two flavors of dynamical quarks on a lattice with the size $N_s^3 \times N_t=16^3 \times 4$, using a renormalization group improved gauge action and a clover improved Wilson quark action. The simulations are made along the lines of constant physics determined in terms of $m_{\rm PS}/m_{\rm V}$ at zero-temperature. We show preliminary results for the spatial string tension in the high temperature phase.

hep-lat↗

arXiv2006

$ρ$ meson decay from the lattice

We present preliminary results on the $ρ$ meson decay width estimated from the scattering phase shift of the I=1 two-pion system. The phase shift is calculated by the finite size formula for non-zero total momentum frame (the moving frame) derived by Rummukainen and Gottlieb, using the $N_f=2$ improved Wilson fermion action at $m_π/m_ρ=0.41$ and $L=2.53 {\rm fm}$.

hep-lat↗

arXiv2006

An estimate of the eta and eta-prime meson masses in Nf=2+1 lattice QCD

Masses of the eta and eta-prime mesons are estimated in Nf=2+1 lattice QCD with the non-perturbatively O(a) improved Wilson quark action and the Iwasaki RG-improved gluon action, using CP-PACS/JLQCD configurations on a 16^3 x 32 lattice at beta=1.83 (lattice spacing is 0.122 fm). We apply a stochastic noise estimator technique combined with smearing method to evaluate correlators among flavor SU(2) singlet pseudoscalar operators and strange pseudoscalar operators for 10 combinations of up/down and strange quark masses. The correlator matrix is then diagonalized to identify signals for mass eigenstates. Masses of the ground state and the first excited state extrapolated to the physical point are m_eta= 0.545(16) GeV and m_eta-prime= 0.871(46) GeV, being close to the experimental values of the eta and eta-prime masses.

hep-lat↗

arXiv2006

Calculation of Neutron EDM in quenched and full QCD

We report on a direct lattice calculation of the neutron EDM(NEDM) using the external electric field method in both quenched and full QCD. In quenched QCD, we use a $24^3\times 32$ lattice at $β=2.6$ with the Iwasaki gauge action and the clover fermion action to examine the viability of this method. In particular we investigate possible effects of violation of the periodic boundary condition of the external electric field on the NEDM signal. We also study the quark mass dependence of NEDM in quenched QCD, and observe that NEDM seems to remain non-zero toward the chiral limit because of the quenched artifact. In 2-flavor full QCD we employ configurations generated by the CP-PACS collaboration on a $24^3\times 48$ lattice at $β=2.1$ with the same gluon and quark actions as in the quenched case. Since the number of configurations is limited, we employ 8 different source points per one configuration and take an average over them. Our preliminary result at three quark masses ($m_{PS}/m_V\simeq 0.81, 0.76, 0.69$) indicates that non-zero value for NEDM can be obtained in full QCD. Statistical errors, however, are still too large to show the theoretically expected behaviour for NEDM in full QCD that it vanishes in the chiral limit.

hep-lat↗