arXiv subjects

N. Tsutsui

Publications and source records attributed to N. Tsutsui.

At least 19 recordsLinked to original sources

arXiv2008

Light quark masses from unquenched lattice QCD

We calculate the light meson spectrum and the light quark masses by lattice QCD simulation, treating all light quarks dynamically and employing the Iwasaki gluon action and the nonperturbatively O(a)-improved Wilson quark action. The calculations are made at the squared lattice spacings at an equal distance a^2~0.005, 0.01 and 0.015 fm^2, and the continuum limit is taken assuming an O(a^2) discretization error. The light meson spectrum is consistent with experiment. The up, down and strange quark masses in the \bar{MS} scheme at 2 GeV are \bar{m}=(m_{u}+m_{d})/2=3.55^{+0.65}_{-0.28} MeV and m_s=90.1^{+17.2}_{-6.1} MeV where the error includes statistical and all systematic errors added in quadrature. These values contain the previous estimates obtained with the dynamical u and d quarks within the error.

hep-lat↗

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↗

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

Nonperturbative $O(a)$ improvement of the Wilson quark action with the RG-improved gauge action using the Schrödinger functional method

We perform a nonperturbative determination of the $O(a)$-improvement coefficient $c_{\rm SW}$ and the critical hopping parameter $κ_c$ for $N_f$=3, 2, 0 flavor QCD with the RG-improved gauge action using the Schrödinger functional method. In order to interpolate $c_{\rm SW}$ and $κ_c$ as a function of the bare coupling, a wide range of $β$ from the weak coupling region to the moderately strong coupling points used in large-scale simulations is studied. Corrections at finite lattice size of $O(a/L)$ turned out to be large for the RG-improved gauge action, and hence we make the determination at a size fixed in physical units using a modified improvement condition. This enables us to avoid $O(a)$ scaling violations which would remain in physical observables if $c_{\rm SW}$ determined for a fixed lattice size $L/a$ is used in numerical simulations.

hep-lat↗

arXiv2005

Pion form factors in two-flavor QCD

We present a calculation of pion electromagnetic and scalar form factors in two-flavor QCD with the non-perturbatively O(a)-improved Wilson fermion. Chiral extrapolation of the corresponding charge radius is discussed based on the chiral perturbation theory.

hep-lat↗

arXiv2005

Kaon semileptonic decay form factors in two-flavor QCD

We present a calculation of the kaon form factors in two-flavor QCD with the non-perturbatively $O(a)$-improved Wilson quark action. In order to achieve a few percent accuracy in the study of SU(3) breaking effects, we use a set of double ratios of the matrix elements, with which the bulk of the statistical fluctuation and the multiplicative renormalization factors cancel.

hep-lat↗

arXiv2005

The PACS-CS Project

We describe our plan to develop a large-scale cluster system with a peak speed of 14.3Tflops for lattice QCD at the Center for Computational Sciences, University of Tsukuba, as a successor to the current 0.6Tflops CP-PACS computer. The system consist of 2560 nodes connected by a 16x16x10 three-dimensional hyper crossbar network. Each node has a single low-voltage 2.8GHz Xeon processor and 2GBytes of memory with 6.4GBytes/sec bandwidth, and 160 GBytes of disk in RAID1 mode. The network link in each of the three directions is made of dual Gigabit Ethernet with the peak throughput of 250MByte/sec. Hence each node has an aggregate network bandwidth of 750MByte/sec. The system will run under Linux and SCore, and an extension of the PM driver is developed for the network. The system will be developed jointly with Hitachi Limited. The installation is scheduled in the first quarter of Japanese Fiscal 2006 (April-June 2006) and the start of operation is expected in July 2006.

hep-lat↗

arXiv2005

Light hadron spectrum and quark masses in 2+1 flavor QCD

CP-PACS and JLQCD collaborations are carrying out a joint project of the 2+1 flavor full QCD simulation. Gauge configurations are generated for the non-perturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action using PHMC algorithm at three lattice spacings, $a\sim 0.076$, 0.010 and 0.122 fm, with a fixed physical volume $(2.0 fm)^3$. We present analysis for the light meson spectrum and quark masses in the continuum limit, which are determined using data obtained from the simulations at the two coarser lattices. Our simulations reproduce experimental values of meson masses. The ud and strange quark masses turn out to be $m_{ud}^{\bar{MS}}(μ=2 GeV)=3.34(23) MeV$ and $m_s^{\bar{MS}}(μ=2 GeV)=86.7(5.9) MeV$. We also show preliminary results at our finest lattice spacing for which simulations are still being continued.

hep-lat↗

arXiv2005

Non-perturbative O(a)-improvement of Wilson quark action in three-flavor QCD with plaquette gauge action

We perform a non-perturbative determination of the O(a)-improvement coefficient c_SW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of β=12.0-5.2 on a single lattice size of 8^3x16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for c_SW and the critical hopping parameter K_c as a function of the bare coupling. This enables us to remove O(a) scaling violation from physical observables in future numerical simulation in the wide range of β. Our analysis with a perturbatively modified improvement condition for c_SW suggests that finite volume effects in c_SW are not large on the 8^3x16 lattice. We investigate N_f dependence of c_SW by additional simulations for N_f=4, 2 and 0 at β=9.6. As a preparatory step for this study, we also determine c_SW in two-flavor QCD at β=5.2. At this β, several groups carried out large-scale calculations of the hadron spectrum, while no systematic determination of c_SW has been performed.

hep-lat↗

arXiv2004

Light hadron spectrum in 2+1 flavor full QCD by CP-PACS and JLQCD Collaborations

CP-PACS and JLQCD Collaborations are carrying out a joint project of the 2+1 flavor full QCD with the RG-improved gauge action and the non-perturbatively ${\cal O}(a)$-improved Wilson quark action. This simulation removes quenching effects of all three light quarks, which is the last major uncertainty in lattice QCD. In this report we present our results for the light meson spectrum and quark masses on a $20^3\times 40$ lattice at the lattice spacing $a\simeq 0.10$ fm.

hep-lat↗

arXiv2004

Bulk first-order phase transition in three-flavor lattice QCD with $O(a)$-improved Wilson fermion action at zero temperature

Three-flavor QCD simulation with the $O(a)$-improved Wilson fermion action is made employing an exact fermion algorithm developed for odd number of quark flavors. For the plaquette gauge action, an unexpected first-order phase transition is found in the strong coupling regime ($β\lesssim$ 5.0) at relatively heavy quark masses ($m_{\mathrm{PS}}/m_{\mathrm{V}}\sim$ 0.74--0.87). Strong metastability persists on a large lattice of size $12^3\times 32$, which indicates that the transition has a bulk nature. The phase gap becomes smaller toward weaker couplings and vanishes at $β\simeq 5.0$, which corresponds to a lattice spacing $a\simeq$ 0.1 fm. The phase transition is not found if the improved gauge actions are employed. Our results imply that realistic simulations of QCD with three flavors of dynamical Wilson-type fermions at lattice spacings in the range $a=$ 0.1--0.2 fm require use of improved gauge actions. Possible origins of the phase transition is discussed.

hep-lat↗

arXiv2004

Lattice QCD calculation of the proton decay matrix element in the continuum limit

We present a quenched lattice QCD calculation of the αand βparameters 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\approx 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, |α(NDR,2GeV)|=0.0090(09)(^{+5}_{-19})GeV^3 and |β(NDR,2GeV)|=0.0096(09)(^{+6}_{-20})GeV^3 with αand βin a relatively opposite sign, where the first error is statistical and the second is due to the uncertainty in the determination of the physical scale.

hep-lat↗

arXiv2003

Lattice QCD on Earth Simulator

We report on coding and performance of our polynomial hybrid Monte Carlo program on the Earth Simulator. At present the entire program achieves 25--40% efficiency. An analysis of overheads shows that a tuning of inter-node communications is required for further improvement.

hep-lat↗

arXiv2003

B-Bbar mixing in unquenched lattice QCD

We present an unquenched lattice calculation for the $B^0-\bar{B}^0$ transition amplitude. The calculation, carried out at an inverse lattice spacing $1/a$ = 2.22(4) GeV, incorporates two flavors of dynamical quarks described by the fully $O(a)$-improved Wilson fermion action and heavy quarks described by NRQCD. A particular attention is paid to the uncertainty that arises from the chiral extrapolation, especially the effect of pion loops, for light quarks, which we find could be sizable for the leptonic decay of the $B_d$ meson, whereas it is small for the $B_s$ meson and the $B$ parameters. We obtain $f_{B_d}=191(10)(^{+12}_{-22})$ MeV, $f_{B_s}/f_{B_d}=1.13(3)(^{+13}_{-\ 2})$, $B_{B_d}(m_b)=0.836(27)(^{+56}_{-62})$, $B_{B_s}/B_{B_d}=1.017(16)(^{+56}_{-17})$, $ξ=1.14(3)(^{+13}_{- 2})$, where the first error is statistical, and the second is systematic, including uncertainties due to chiral extrapolation, finite lattice spacing, heavy quark expansion and perturbative operator matching.

hep-ph↗

arXiv2003

Light hadron spectrum in three-flavor QCD with O(a)-improved Wilson quark action

We report on a calculation of the light hadron spectrum and quark masses in three-flavor dynamical QCD using the non-perturbatively O(a)-improved Wilson quark action and a renormalization-group improved gauge action. Simulations are carried out on a 16^3 \times 32 lattice at β=1.9, where a^{-1} \simeq 2GeV, with 6 ud quark masses corresponding to m_{pi}/m_{rho} \simeq 0.64-0.77 and 2 s quark masses close to the physical value. We observe that the inclusion of dynamical strange quark brings the lattice QCD meson spectrum to good agreement with experiment. Dynamical strange quarks also lead to a reduction of the uds quark masses by about 15%.

hep-lat↗

arXiv2003

Study of finite volume effects in the non-perturbative determination of $\csw$ with the SF method in full three-flavor lattice QCD

The non-perturbative $\csw$ determined by the Schrödinger functional (SF) method with the RG-improved gauge action in dynamical $N_f=3$ QCD shows a finite volume effect when the numerical simulations are carried out at a constant lattice size $L/a$. We remove the unwanted finite volume effect by keeping physical lattice extent $L$ at a constant. The details of the method and the result obtained for non-perturbative $\csw$ with a constant $L$ are reported.

hep-lat↗

arXiv2003

Continuum limit of proton decay matrix elements in quenched lattice QCD

We present a lattice QCD calculation of the parameters αand βwhich are necessary in the theoretical estimation of the proton lifetime in grand unified theories (GUTs) using chiral lagrangian approach. The simulation is carried out using the Wilson quark action at three gauge coupling constants in the quenched approximation. We obtain |α(2GeV)|=0.0091(08)(^{+10}_{-19})GeV^3 and |β(2GeV)|=0.0098(08)(^{+10}_{-20})GeV^3 in the continuum limit where the first error is statistical and the second one is due to scale setting.

hep-lat↗

arXiv2003

Light hadron spectroscopy with two flavors of $O(a)$-improved dynamical quarks

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 ρmeson mass, on a 20^3\times 48 lattice. At each of five sea quark masses corresponding to m_{PS}/m_{V} \simeq 0.8-0.6, we generate 12000 trajectories using the symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 12^3 \times 48, 16^3 \times 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 m_{ud}^{MS}(2GeV) =3.223(+0.046/-0.069)MeV and m_s^{MS}(2GeV)=84.5(+12.0/-1.7)MeV which are about 20% smaller than in quenched QCD.

hep-lat↗