Y. Namekawa

Physical Point Simulation in 2+1 Flavor Lattice QCD

We present the results of the physical point simulation in 2+1 flavor lattice QCD with the nonperturbatively O(a)-improved Wilson quark action and the Iwasaki gauge action at {beta} = 1.9 on a 32{sup 3} x 64 lattice. The physical quark masses together with the lattice spacing is determined with m{sub {pi}}, m{sub K} and m{sub {Omega}} as physical inputs. There are two key algorithmic ingredients to make possible the direct simulation at the physical point: One is the mass-preconditioned domain-decomposed HMC algorithm to reduce the computational cost. The other is the reweighting technique to adjust the hopping parameters exactly to the physical point. The physics results include the hadron spectrum, the quark masses and the pseudoscalar meson decay constants. The renormalization factors are nonperturbatively evaluated with the Schroedinger functional method. The results are compared with the previous ones obtained by the chiral extrapolation method.

ρ meson decay in 2+1 flavor lattice QCD

(PACS-CS Collaboration) 1 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan 2 Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan 3 Department of Physics, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan 4 RIKEN Advanced Institute for Computational Science, Kobe, Hyogo 650-0047, Japan 5 Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya, Aichi 464-8602, Japan (Dated: November 28, 2011)

Precise determination of the strong coupling constant in Nf = 2+1 lattice QCD with the Schrödinger functional scheme

We present an evaluation of the running coupling constant for Nf = 2+1 QCD. The Schrodinger functional scheme is used as the intermediate scheme to carry out non-perturbative running from the low energy region, where physical scale is introduced, to deep in the high energy perturbative region, where conversion to the scheme is safely performed. Possible systematic errors due to the use of perturbation theory occur only in the conversion from three-flavor to four-flavor running coupling constant near the charm mass threshold, where higher order terms beyond 5th order in the β function may not be negligible. For numerical simulations we adopted Iwasaki gauge action and non-perturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy region and three lattice spacings to take the continuum limit at each scale. A physical scale is introduced from the previous Nf = 2+1 simulation of the CP-PACS/JL-QCD collaboration [1], which covered the up-down quark mass range heavier than mπ ~ 500 MeV. Our final result is = 0.12047(81)(48)(+0−173) and = 239(10)(6)(+0−22) MeV .

Charm quark system at the physical point of 2+1 flavor lattice QCD

1 Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan 2 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan 3 Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan 4 Riken BNL Research Center, Brookhaven National Laboratory, Upton, New York 11973, USA 5 RIKEN Advanced Institute for Computational Science, Kobe, Hyogo 650-0047, Japan (Dated: January 20, 2013)

SU(2) and SU(3) chiral perturbation theory analyses on baryon masses in 2 + 1 flavor lattice QCD

We investigate the quark mass dependence of baryon masses in 2+1 flavor lattice QCD using SU(3) heavy baryon chiral perturbation theory up to one-loop order. The baryon mass data used for the analyses are obtained for the degenerate up-down quark mass of 3 to 24 MeV and two choices of the strange quark mass around the physical value. We find that the SU(3) chiral expansion fails to describe both the octet and the decuplet baryon data if phenomenological values are employed for the meson-baryon couplings. The SU(2) case is also examined for the nucleon. We observe that higher order terms are controlled only around the physical point. We also evaluate finite size effects using SU(3) heavy baryon chiral perturbation theory, finding small values of order 1% even at the physical point.

Non-perturbative renormalization of quark mass in N-f=2+1 QCD with the Schrodinger functional scheme

We present an evaluation of the quark mass renormalization factor for Nf = 2 + 1 QCD. The Schrödinger functional scheme is employed as the intermediate scheme to carry out non-perturbative running from the low energy region, where renormalization of bare mass is performed on the lattice, to deep in the high energy perturbative region, where the conversion to the renormalization group invariant mass or the

Light hadron spectroscopy in two-flavor QCD with small sea quark masses

\overline {\text{MS}}

2+1 Flavor QCD Simulation on a

scheme is safely carried out. For numerical simulations we adopted the Iwasaki gauge action and nonperturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy regions and three lattice spacings to take the continuum limit at each scale. The regularization independent step scaling function of the quark mass for the Nf = 2 + 1 QCD is obtained in the continuum limit. Renormalization factors for the pseudo scalar density and the axial vector current are also evaluated for the same action and the bare couplings as two recent large scale Nf = 2 + 1 simulations; previous work of the CP -PACS/JLQCD collaboration, which covered the up-down quark mass range heavier than mπ ∼ 500 MeV and that of PACS-CS collaboration for much lighter quark masses down to mπ = 155MeV. The quark mass renormalization factor is used to renormalize bare PCAC masses in these simulations.

96^4

We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to m{sub PS}/m{sub V}=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 m{sub PS}/m{sub V}=0.80-0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fail, the Wilson ChPT (WChPT) that includes a{sup 2} 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 m{sub PS}/m{sub V} > or approx. 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%, m{sub ud}{sup MS-bar}({mu}=2 GeV)=3.11(17) [MeV] in the continuum limit.

Lattice

We generate