Hidekatsu Nemura

Hadron–hadron interactions from imaginary-time Nambu–Bethe–Salpeter wave function on the lattice

Abstract Imaginary-time Nambu–Bethe–Salpeter (NBS) wave function is introduced to extend our previous approach for hadron–hadron interactions on the lattice. Scattering states of hadrons with different energies encoded in the NBS wave function are utilized to extract non-local hadron–hadron potential. “The ground state saturation”, which is commonly used in lattice QCD but is hard to be achieved for multi-baryons, is not required. We demonstrate that the present method works efficiently for the nucleon–nucleon interaction (the potential and the phase shift) in the S 0 1 channel.

Two-baryon potentials and H-dibaryon from 3-flavor lattice QCD simulations

Abstract Baryon–baryon potentials are obtained from 3-flavor QCD simulations with the lattice volume L ≃ 4 fm , the lattice spacing a ≃ 0.12 fm , and the pseudo-scalar-meson mass M ps = 469 – 1171 MeV . The NN scattering phase-shifts and the mass of H-dibaryon in the flavor SU ( 3 ) limit are extracted from the resultant potentials by solving the Schrodinger equation. The NN phase-shifts in the SU ( 3 ) limit is shown to have qualitatively similar behavior as the experimental data. A bound H-dibaryon in the SU ( 3 ) limit is found to exist in the flavor-singlet J P = 0 + channel with the binding energy of about 26 MeV for the lightest quark mass M ps = 469 MeV . Effect of flavor SU ( 3 ) symmetry breaking on the H-dibaryon is estimated by solving the coupled-channel Schrodinger equation for Λ Λ – N Ξ – Σ Σ with the physical baryon masses and the potential matrix obtained in the SU ( 3 ) limit: a resonant H-dibaryon is found between ΛΛ and NΞ thresholds in this treatment.

Spin-2 NΩ dibaryon from lattice QCD

Abstract We investigate properties of the N (nucleon) – Ω (Omega) interaction in lattice QCD to seek for possible dibaryon states in the strangeness −3 channel. We calculate the NΩ potential through the equal-time Nambu–Bethe–Salpeter wave function in 2 + 1 flavor lattice QCD with the renormalization group improved Iwasaki gauge action and the nonperturbatively O ( a ) improved Wilson quark action at the lattice spacing a ≃ 0.12 fm on a ( 1.9 fm ) 3 × 3.8 fm lattice. The ud and s quark masses in our study correspond to m π = 875 ( 1 ) MeV and m K = 916 ( 1 ) MeV . At these parameter values, the central potential in the S-wave with the spin 2 shows attractions at all distances. By solving the Schrodinger equation with this potential, we find one bound state whose binding energy is 18.9 ( 5.0 ) ( − 1.8 + 12.1 ) MeV , where the first error is the statistical one, while the second represents the systematic error.

Mirage in Temporal Correlation functions for Baryon-Baryon Interactions in Lattice QCD

A bstractSingle state saturation of the temporal correlation function is a key condition to extract physical observables such as energies and matrix elements of hadrons from lattice QCD simulations. A method commonly employed to check the saturation is to seek for a plateau of the observables for large Euclidean time. Identifying the plateau in the cases having nearby states, however, is non-trivial and one may even be misled by a fake plateau. Such a situation takes place typically for a system with two or more baryons. In this study, we demonstrate explicitly the danger from a possible fake plateau in the temporal correlation functions mainly for two baryons (ΞΞ and N N ), and three and four baryons (3He and 4He) as well, employing (2+1)-flavor lattice QCD at mπ = 0.51GeV on four lattice volumes with L = 2.9, 3.6, 4.3 and 5.8 fm. Caution is required when drawing conclusions about the bound N N , 3N and 4N systems based only on the standard plateau fitting of the temporal correlation functions.n

Spin–orbit force from lattice QCD

Abstract We present a first attempt to determine nucleon–nucleon potentials in the parity-odd sector, which appear in the P 1 1 , P 0 3 , P 1 3 , P 2 3 – F 2 3 channels, in N f = 2 lattice QCD simulations. These potentials are constructed from the Nambu–Bethe–Salpeter wave functions for J P = 0 − , 1 − and 2 − , which correspond to the A 1 − , T 1 − and T 2 − ⊕ E − representation of the cubic group, respectively. We have found a large and attractive spin–orbit potential V LS ( r ) in the isospin-triplet channel, which is qualitatively consistent with the phenomenological determination from the experimental scattering phase shifts. The potentials obtained from lattice QCD are used to calculate the scattering phase shifts in the P 1 1 , P 0 3 , P 1 3 and P 2 3 – F 2 3 channels. The strong attractive spin–orbit force and a weak repulsive central force in spin-triplet P -wave channels lead to an attraction in the P 2 3 channel, which is related to the P -wave neutron paring in neutron stars.

Charmed tetraquarks Tcc and Tcs from dynamical lattice QCD simulations

Abstract Charmed tetraquarks T c c = ( c c u ¯ d ¯ ) and T c s = ( c s u ¯ d ¯ ) are studied through the S-wave meson–meson interactions, D–D, K ¯ –D, D– D ⁎ and K ¯ – D ⁎ , on the basis of the ( 2 + 1 ) -flavor lattice QCD simulations with the pion mass m π ≃ 410 , 570 and 700 MeV. For the charm quark, the relativistic heavy quark action is employed to treat its dynamics on the lattice. Using the HAL QCD method, we extract the S-wave potentials in lattice QCD simulations, from which the meson–meson scattering phase shifts are calculated. The phase shifts in the isospin triplet ( I = 1 ) channels indicate repulsive interactions, while those in the I = 0 channels suggest attraction, growing as m π decreases. This is particularly prominent in the T c c ( J P = 1 + , I = 0 ) channel, though neither bound state nor resonance are found in the range m π = 410 – 700 MeV . We make a qualitative comparison of our results with the phenomenological diquark picture.

OpenCL vs OpenACC: Lessons from Development of Lattice QCD Simulation Code☆

Abstract OpenCL and OpenACC are generic frameworks for heterogeneous programming using CPU and accelerator devices such as GPUs. They have contrasting features: the former explicitly controls devices through API functions, while the latter generates such procedures along a guide of the directives inserted by a programmer. In this paper, we apply these two frameworks to a general-purpose code set for numerical simulations of lattice QCD, which is a computational physics of elementary particles based on the Monte Carlo method. The fermion matrix inversion, which is usually the most time-consuming part of the lattice QCD simulations, is offloaded to the accelerator devices. From a viewpoint of constructing reusable components based on the object-oriented programming and also tuning the code to achieve high performance, we discuss feasibility of these frameworks through the practical implementations.

Omega-omega interaction from 2+1-flavor lattice quantum chromodynamics

Letter Omega-Omega interaction from 2+1-flavor lattice quantum chromodynamics Masanori Yamada1,∗, Kenji Sasaki2, Sinya Aoki2,3, Takumi Doi4, Tetsuo Hatsuda4,5, Yoichi Ikeda4, Takashi Inoue6, Noriyoshi Ishii7, Keiko Murano7, and Hidekatsu Nemura1,2 (on behalf of the HAL QCD Collaboration) 1Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571, Japan 2Center for Computational Sciences, University of Tsukuba, Tsukuba 305-8577, Japan 3Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan 4Theoretical Research Division, Nishina Center, RIKEN, Wako 351-0198, Japan 5Kavli IPMU (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583, Japan 6Nihon University, College of Bioresource Sciences, Fujisawa 252-0880, Japan 7Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki 567-0047, Japan ∗E-mail: sinyamada@het.ph.tsukuba.ac.jp

Instructive discussion of an effective block algorithm for baryon–baryon correlators

Abstract We describe an approach for the efficient calculation of a large number of four-point correlation functions for various baryon–baryon ( B B ) channels, which are the primary quantities for studying the nuclear and hyperonic nuclear forces from lattice quantum chromodynamics. Using the four-point correlation function of a proton- Λ system as a specific example, we discuss how an effective block algorithm significantly reduces the number of iterations. The effective block algorithm is applied to calculate 52 channels of the four-point correlation functions from nucleon–nucleon to Ξ – Ξ , in order to study the complete set of isospin symmetric B B interactions. The elapsed times measured for hybrid parallel computation on BlueGene/Q demonstrate that the performance of the present algorithm is reasonable for various combinations of the number of OpenMP threads and the number of MPI nodes. The numerical results are compared with the results obtained using the unified contraction algorithm for all computed sites of the 52 four-point correlators.

Development of Lattice QCD Simulation Code Set “Bridge++” on Accelerators

Abstract We are developing a new code set “Bridge++” for lattice QCD (Quantum Chromodynamics) simulations. It aims at an extensible, readable, and portable workbench, while achieving high performance. Bridge++ covers popular lattice actions and numerical algorithms. The code set is constructed in C++ with an object oriented programming. In this paper, we describe our code design focusing on the use of accelerators such as GPGPUs. For portability our implemen- tation employs OpenCL to control the devices while encapsulates the details of manipulation by providing generalized interfaces. The code is successfully applied to several recent accelerators.