Searcharxiv⌕ Search

arXiv subjects

Yoshinobu Kuramashi

Publications and source records attributed to Yoshinobu Kuramashi.

At least 73 records · Page 4Linked to original sources
arXiv2018

Finite-volume correction on the hadronic vacuum polarization contribution to muon g-2 in lattice QCD

We study the finite-volume correction on the hadronic vacuum polarization contribution to the muon g-2 ($a_μ^{\rm hvp}$) in lattice QCD at (near) physical pion mass using two different volumes: $(5.4~{\rm fm})^4$ and $(8.1~{\rm fm})^4$. We use an optimized AMA technique for noise reduction on $N_f=2+1$ PACS gauge configurations with stout-smeared clover-Wilson fermion action and Iwasaki gauge action at a single lattice cut-off $a^{-1}=2.33$ GeV. The calculation is performed for the quark-connected light-quark contribution in the isospin symmetric limit. We take into account the effects of backward state propagation by extending a temporal boundary condition. In addition we study a quark-mass correction to tune to the exactly same physical pion mass on different volume and compare those correction with chiral perturbation. We find $10(26)\times10^{-10}$ difference for light quark $a_μ^{\rm hvp}$ between $(5.4~{\rm fm})^4$ and $(8.1~{\rm fm})^4$ lattice in 146 MeV pion.

hep-lat↗
arXiv2018

Utility of geometry in lattice QCD simulations

We propose a way to improve the resolution of the spatial momentum and the time interval for hadron propagators utilizing the lattice geometry. We demonstrate the validity of the method presenting results for pseudoscalar meson energies with and without finite momenta in a large-scale quenched QCD simulation. The method should be useful especially for master-field simulations.

hep-lat↗
arXiv2018

Tensor network formulation for two-dimensional lattice $\mathcal{N}=1$ Wess-Zumino model

Supersymmetric models with spontaneous supersymmetry breaking suffer from the notorious sign problem in stochastic approaches. By contrast, the tensor network approaches do not have such a problem since they are based on deterministic procedures. In this work, we present a tensor network formulation of the two-dimensional lattice $\mathcal{N}=1$ Wess-Zumino model while showing that numerical results agree with the exact solutions for the free case.

hep-lat↗
arXiv2017

Relation between scattering amplitude and Bethe-Salpeter wave function in quantum field theory

We reexamine the relations between the Bethe-Salpeter (BS) wave function of two particles, the on-shell scattering amplitude, and the effective potential in quantum filed theory. It is emphasized that there is an exact relation between the BS wave function inside the interaction range and the scattering amplitude, and the reduced BS wave function, which is defined in this article, plays an essential role in this relation. Based on the exact relation, we show that the solution of Schrödinger equation with the effective potential gives us a correct on-shell scattering amplitude only at the momentum where the effective potential is calculated, while wrong results are obtained from the Schrödinger equation at general momenta. We also discuss about a momentum expansion of the reduced BS wave function and an uncertainty of the scattering amplitude stemming from the choice of the interpolating operator in the BS wave function. The theoretical conclusion obtained in this article could give hints to understand the inconsistency observed in lattice QCD calculation of the two-nucleon channels with different approaches.

hep-lat↗
arXiv2017

Berezinskii-Kosterlitz-Thouless transition in lattice Schwinger model with one flavor of Wilson fermion

We have made a detailed study of the phase structure for lattice Schwinger model with one flavor of Wilson fermion on the $(m,g)$ plane. For numerical investigation, we develop a decorated tensor renormalization method for lattice gauge theories with fermions incorporating the Grassmann tensor renormalization. Our algorithm manifestly preserves rotation and reflection symmetries. We find not only a parity-broken phase but also a Berezinskii-Kosterlitz-Thouless (BKT) transition by evaluating the central charge and an expectation value of a projection operator into the parity-odd subspace. The BKT phase boundaries converge into the degenerated doubler pole $(m,g)=(-2,0)$, while the parity-breaking transition line ends at the physical pole $(m,g)=(0,0)$. In addition, our analysis of scaling dimensions indicates that a conformal field theory with $\mathrm{SU}(2)$ symmetry arises on the line of $m=-2$.

hep-lat↗
arXiv2017

Application of tensor network method to two dimensional lattice $\mathcal{N}=1$ Wess-Zumino model

We study a tensor network formulation of the two dimensional lattice $\mathcal{N}=1$ Wess-Zumino model with Wilson derivatives for both fermions and bosons. The tensor renormalization group allows us to compute the partition function without the sign problem, and basic ideas to obtain a tensor network for both fermion and scalar boson systems were already given in previous works. In addition to improving the methods, we have constructed a tensor network representation of the model including the Yukawa-type interaction of Majorana fermions and real scalar bosons. We present some numerical results.

hep-lat↗
arXiv2017

Nucleon structure from 2+1 flavor lattice QCD near the physical point

We present an update on our results of nucleon form factors measured on a large-volume lattice $(8.1\rm{fm})^4$ at almost the physical point in 2+1 flavor QCD. The configurations are generated with the stout-smeared $\mathcal{O}(a)$ improved Wilson quark action and Iwasaki gauge action at $β= 1.82$, which corresponds to the lattice spacing of 0.085 fm. The pion mass at the simulation point is about 145 MeV. We determine the iso- vector electric radius and magnetic moment from nucleon electric ($G_E$) and magnetic ($G_M$) form factors. We also report on preliminary results of the axial-vector ($F_A$), induced pseudo-scalar ($F_P$) and pseudo-scalar ($G_P$) form factors in order to verify the axial Ward- Takahashi identity in terms of the nucleon matrix elements, which may be called as the generalized Goldberger-Treiman relation.

hep-lat↗
arXiv2017

Continuum extrapolation of critical point for finite temperature QCD with Nf=3

We study the critical point for finite temperature Nf=3 QCD using several temporal lattice sizes up to 10. In the study, the Iwasaki gauge action and non-perturbatively O(a) improved Wilson fermions are employed. We estimate the critical temperature and the upper bound of the critical pseudo-scalar meson mass.

hep-lat↗
arXiv2017

Critical point phase transition for finite temperature 3-flavor QCD with non-perturbatively O($a$) improved Wilson fermions at $N_{\rm t}=10$

We study the finite temperature phase structure for three-flavor QCD with a focus on locating the critical point which separates crossover and first order phase transition region in the chiral regime of the Columbia plot. In this study, we employ the Iwasaki gauge action and the non-perturvatively O($a$) improved Wilson-Clover fermion action. We discuss the finite size scaling analysis including the mixing of magnetization-like and energy-like observables. We carry out the continuum extrapolation of the critical point using newly generated data at $N_{\rm t}=8$, $10$ and estimate the upper bound of the critical pseudo-scalar meson mass $m_{\rm PS,E} \lesssim 170 {\rm MeV}$ and the critical temperature $T_{\rm E}=134(3){\rm MeV}$. Our estimate of the upper bound is derived from the existence of the critical point as an edge of the 1st order phase transition while that of the staggered-type fermions is based on its absence.

hep-lat↗
arXiv2017

Mixed Precision Solver Scalable to 16000 MPI Processes for Lattice Quantum Chromodynamics Simulations on the Oakforest-PACS System

Lattice Quantum Chromodynamics (Lattice QCD) is a quantum field theory on a finite discretized space-time box so as to numerically compute the dynamics of quarks and gluons to explore the nature of subatomic world. Solving the equation of motion of quarks (quark solver) is the most compute-intensive part of the lattice QCD simulations and is one of the legacy HPC applications. We have developed a mixed-precision quark solver for a large Intel Xeon Phi (KNL) system named "Oakforest-PACS", employing the $O(a)$-improved Wilson quarks as the discretized equation of motion. The nested-BiCGSTab algorithm for the solver was implemented and optimized using mixed-precision, communication-computation overlapping with MPI-offloading, SIMD vectorization, and thread stealing techniques. The solver achieved 2.6 PFLOPS in the single-precision part on a $400^3\times 800$ lattice using 16000 MPI processes on 8000 nodes on the system.

physics.comp-ph↗
arXiv2017

Systematic study of operator dependence in nucleus calculation at large quark mass

Recently it is claimed that there is a significant systematic error from excited state contributions in the nucleus correlation functions by comparing with calculations using the exponential and wall source operators. However, the wall source result is obtained in much earlier time than the plateau region. In order to investigate the systematic error in the plateau region, we calculate the correlation functions with both the operators in quenched QCD at 0.8 GeV pion mass and in $N_f=2+1$ QCD at 0.7 GeV pion mass in high accuracy. In this report we present preliminary results of those calculations, and show that the energy shift obtained from the two sources agree with each other, if those are determined from a region, where both the nucleon and two-nucleon correlation functions have plateaus.

hep-lat↗
arXiv2016

A performance evaluation of CCS QCD Benchmark on the COMA (Intel(R) Xeon Phi$^{TM}$, KNC) system

The most computationally demanding part of Lattice QCD simulations is solving quark propagators. Quark propagators are typically obtained with a linear equation solver utilizing HPC machines. The CCS QCD Benchmark is a benchmark program solving the Wilson-Clover quark propagator, and is developed at the Center for Computational Sciences (CCS), University of Tsukuba. We optimized the benchmark program for a \Intel \XeonPhi (Knights Corner, KNC) system named "COMA (PACS-IX)" at CCS Tsukuba under the Intel Parallel Computing Center program. A single precision BiCGStab solver with the overlapped Restricted Additive Schwarz (RAS) preconditioner was implemented using SIMD intrinsics, OpenMP and MPI in the offload mode. With the reverse-offloading technique, we could reduce the communication and offloading overheads. We observed a performance of $\sim 200$ GFlops sustained for the Wilson-Clover hopping matrix multiplication on the lattice sizes larger than $24^3\times 32$ on a sinlge card of the COMA system. A good weak scaling perofmace was observed on the local lattice sizes larger than $24^3\times 32$.

hep-lat↗
arXiv2016

Update on Nf=3 finite temperature QCD phase structure with Wilson-Clover fermion action

We present an update of the finite temperature phase structure analysis for three flavor QCD. In the study the Iwasaki gauge action and non-perturvatively O($a$) improved Wilson-Clover fermion action are employed. We discuss finite size scaling analysis including mixings of magnetization-like and energy-like observables. Preliminary results are shown of the continuum limit of the critical point using newly generated data at Nt=8,10, including estimates of the critical pseudo-scalar meson mass and critical temperature.

hep-lat↗
arXiv2016

Critical endline of the finite temperature phase transition for 2+1 flavor QCD around the SU(3)-flavor symmetric point

We investigate the critical endline of the finite temperature phase transition of QCD around the SU(3)-flavor symmetric point at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and non-perturbatively $O(a)$-improved Wilson-clover fermion action. The critical endline is determined by using the intersection point of kurtosis, employing the multi-parameter, multi-ensemble reweighting method to calculate observables off the SU(3)-symmetric point, at the temporal size $N_{\rm T}$=6 and lattice spacing as low as $a \approx 0.19$ fm. We confirm that the slope of the critical endline takes the value of $-2$, and find that the second derivative is positive, at the SU(3)-flavor symmetric point on the Columbia plot parametrized with the strange quark mass $m_s$ and degenerated up-down quark mass $m_{\rm l}$.

hep-lat↗
arXiv2015

Curvature of the critical line on the plane of quark chemical potential and pseudo scalar meson mass for three-flavor QCD

We investigate the phase structure of three-flavor QCD in the presence of finite quark chemical potential $μ/T\lesssim1.2$ by using the non-perturbatively $O(a)$ improved Wilson fermion action on lattices with a fixed temporal extent $N_{\rm t}=6$ and varied spatial linear extents $N_{\rm s}=8,10,12$. Especially, we focus on locating the critical end point that characterizes the phase structure, and extracting the curvature of the critical line on the $μ$-$m_π$ plane. For Wilson-type fermions, the correspondence between bare parameters and physical parameters is indirect. Hence we present a strategy to transfer the bare parameter phase structure to the physical one, in order to obtain the curvature. Our conclusion is that the curvature is positive. This implies that, if one starts from a quark mass in the region of crossover at zero chemical potential, one would encounter a first-order phase transition when one raises the chemical potential.

hep-lat↗
arXiv2015

Phase structure of $N_{\rm f}=3$ QCD at finite temperature and density by Wilson-Clover fermions

We investigate the phase structure of 3-flavor QCD in the presence of finite quark chemical potential by using Wilson-Clover fermions. To deal with the complex action with finite density, we adopt the phase reweighting method. In order to survey a wide parameter region, we employ the multi-parameter reweighting method as well as the multi-ensemble reweighting method. Especially, we focus on locating the critical end point that characterizes the phase structure. It is estimated by the kurtosis intersection method for the quark condensate. For Wilson-type fermions, the correspondence between bare parameters and physical parameters is indirect, thus we present a strategy to transfer the bare parameter phase structure to the physical one. We conclude that the curvature with respect to the chemical potential is positive. This implies that, if one starts from a quark mass in the region of crossover at zero chemical potential, one would encounter a first-order phase transition when one raises the chemical potential.

hep-lat↗