arXiv subjects

for HAL QCD Collaboration

Publications and source records attributed to for HAL QCD Collaboration.

At least 19 recordsLinked to original sources

arXiv2018

HAL QCD method and Nucleon-Omega interaction with physical quark masses

In lattice QCD, both direct method and HAL QCD method are used to investigate the two-baryon systems. We show that due to the contamination of the scattering excited states, it is challenging to measure the eigenenergy from the temporal correlation in the direct method, while the HAL QCD method can extract the information of the interaction from both scattering states and ground state by using the spatial correlation. We examine the systematic uncertainty of the derivative expansion in the HAL QCD method, which is found to be well under control at the low energies. By using the time-dependent HAL QCD method, we study the nucleon($N$)-Omega($Ω$) system in the $^5$S$_2$ channel with almost physical quark masses at $m_π\simeq 146$ MeV. We find the interaction is attractive at all distances, which produces a quasi-bound state with the binding energy 1.54(0.30)($^{+0.04}_{-0.10}$) MeV. We also consider the extra Coulomb interaction in the $pΩ^{-}$($^5$S$_2$) system, whose binding energy becomes 2.46(0.34)($^{+0.04}_{-0.01}$) MeV. $NΩ$($^5$S$_2$) dibaryon could be searched through two-particle correlations in the heavy ion collision experiments.

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arXiv2017

Two-baryon systems from HAL QCD method and the mirage in the temporal correlation of the direct method

Both direct and HAL QCD methods are currently used to study the hadron interactions in lattice QCD. In the direct method, the eigen-energy of two-particle is measured from the temporal correlation. Due to the contamination of excited states, however, the direct method suffers from the fake eigen-energy problem, which we call the "mirage problem," while the HAL QCD method can extract information from all elastic states by using the spatial correlation. In this work, we further investigate systematic uncertainties of the HAL QCD method such as the quark source operator dependence, the convergence of the derivative expansion of the non-local interaction kernel, and the single baryon saturation, which are found to be well controlled. We also confirm the consistency between the HAL QCD method and the Lüscher's finite volume formula. Based on the HAL QCD potential, we quantitatively confirm that the mirage plateau in the direct method is indeed caused by the contamination of excited states.

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arXiv2017

Hyperon single-particle potentials from QCD on lattice

We study single-particle potential of hyperons in nuclear medium starting from QCD. First we carry out lattice QCD numerical simulation to extract baryon-baryon interactions from QCD by means of the HAL QCD method. We employ a full QCD gauge configuration ensemble at almost physical point so that hadron masses are nearly physical, e.g. pion mass is 146 MeV, kaon mass is 525 MeV, and nucleon mass is 956 MeV. Then, with some simplifications, we apply the obtained hyperon interactions to the Brueckner-Hartree-Fock theory and calculate single-particle potential of hyperons in nuclear medium $U_{Y}(ρ,k)$. For the symmetric nuclear matter at the normal nuclear matter density, we obtain $U_Λ(ρ_0,0)=-33$ MeV, $U_Σ(ρ_0,0)=+11$ MeV, and $U_Ξ(ρ_0,0)=-6$ MeV. These results are qualitatively compatible with values suggested from experiments. This success is remarkable and encouraging because we are trying to reveal nature of baryon-baryon interactions starting from QCD, and this agreement proves that our approach is essentially correct.

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arXiv2016

Baryon interactions in lattice QCD: the direct method vs. the HAL QCD potential method

We make a detailed comparison between the direct method and the HAL QCD potential method for the baryon-baryon interactions, taking the $ΞΞ$ system at $m_π= 0.51$ GeV in 2+1 flavor QCD and using both smeared and wall quark sources. The energy shift $ΔE_\mathrm{eff}(t)$ in the direct method shows the strong dependence on the choice of quark source operators, which means that the results with either (or both) source are false. The time-dependent HAL QCD method, on the other hand, gives the quark source independent $ΞΞ$ potential, thanks to the derivative expansion of the potential, which absorbs the source dependence to the next leading order correction. The HAL QCD potential predicts the absence of the bound state in the $ΞΞ$($^1$S$_0$) channel at $m_π= 0.51$ GeV, which is also confirmed by the volume dependence of finite volume energy from the potential. We also demonstrate that the origin of the fake plateau in the effective energy shift $ΔE_\mathrm{eff}(t)$ at $t \sim 1$ fm can be clarified by a few low-lying eigenfunctions and eigenvalues on the finite volume derived from the HAL QCD potential, which implies that the ground state saturation of $ΞΞ$($^1$S$_0$) requires $t \sim 10$ fm in the direct method for the smeared source on $(4.3 \ \mathrm{fm})^3$ lattice, while the HAL QCD method does not suffer from such a problem.

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arXiv2016

An implementation of hybrid parallel CUDA code for the hyperonic nuclear forces

We present our recent effort to develop a GPGPU program to calculate 52 channels of the Nambu-Bethe-Salpeter (NBS) wave functions in order to study the baryon interactions, from nucleon-nucleon to $Ξ-Ξ$, from lattice QCD. We adopt CUDA programming to perform the multi-GPU execution on a hybrid parallel programming with MPI and OpenMP. Effective baryon block algorithm is briefly outlined, which calculates efficaciously a large number of NBS wave functions at a time, and three CUDA kernel programs are implemented to materialize the effective baryon block algorithm using GPUs on the single-program multiple-data (SPMD) programming model. In order to parallelize multiple GPUs, we take both two approaches by dividing the time dimension and by dividing the spatial dimensions. Performances are measured using HA-PACS supercomputer in University of Tsukuba, which includes NVIDIA M2090 and NVIDIA K20X GPUs. Strong scaling and weak scaling measured by using both M2090 and K20X GPUs are presented. We find distinct difference between the M2090 and the K20X in the sustained performance measurement of particular kernel executions which utilize the cudaStream objects.

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arXiv2016

$Λ_c-N$ interaction from lattice QCD

We investigate the s-wave $Λ_c-N$ interaction for spin singlet systems($^1S_0$) using the HAL QCD method. In our lattice QCD simulations, we employ gauge configurations generated by the PACS-CS Collaboration at $a = 0.0907(13)$ fm on a $32^3 \times 64$ lattice ($La = 2.902(42)$ fm). We employ two ensembles, one at $m_π= 700(1)$ MeV and the other at $m_π= 570(1)$ MeV to study the quark mass dependence of the $Λ_c-N$ interactions. We calculate a $^1S_0$ central potential not only for the $Λ_c-N$ system but also for $Λ-N$ system to understand the role of heavy charm quarks in $Λ_c-N$ system. We find repulsion at short distance and attraction at mid-range for both the $Λ_c-N$ and the $Λ-N$ potentials. The short range repulsion of the $Λ_c-N$ potential is smaller than that of the $Λ-N$ potential, and the attraction of the $Λ_c-N$ potential is small compared with the $Λ-N$ potential. The phase shift and scattering length calculated with these potentials show that there exist no bound state for both the $Λ_c-N$ and $Λ-N$ systems for $m_π > 570$ MeV.

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arXiv2016

Nuclear physics from QCD on lattice

We have presented a strategy to study nuclei and nuclear matters from first principles, namely, from QCD. We first compute nucleon-nucleon potentials numerically in lattice QCD, and then use them to investigate properties of nuclei and nuclear matter by various methods developed in nuclear physics. As a demonstration that this strategy works, mass and structure of ^4^He, ^16^O and ^40^Ca, and equation of state of nuclear matters are determined with the lattice QCD induced two-nucleon potentials in a heavy quark region as an input. We have found that these nuclei and the symmetric nuclear matter are bound at one quark mass corresponding to the pseudo-scalar meson (pion) mass of 469 MeV (the octet baryon (nucleon) mass of 1161 MeV). The obtained binding energy per nucleon has a uniform mass-number A dependence which is consistent to the Bethe-Weizsacker mass formula qualitatively. The present study demonstrates that our strategy works well to investigate various properties of atomic nuclei and nuclear matter starting from QCD, without depending on models or experimental information about the nuclear force.

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arXiv2015

Lattice QCD studies on baryon interactions from Lüscher's finite volume method and HAL QCD method

A comparative study between the Lüscher's finite volume method and the time-dependent HAL QCD method is given for the $ΞΞ$($^1\mathrm{S}_0$) interaction as an illustrative example. By employing the smeared source and the wall source for the interpolating operators, we show that the effective energy shifts $ΔE_{\rm eff} (t)$ in Lüscher's method do not agree between different sources, yet both exhibit fake plateaux. On the other hand, the interaction kernels $V(\vec{r})$ obtained from the two sources in the HAL QCD method agree with each other already for modest values of $t$. We show that the energy eigenvalues $ΔE(L)$ in finite lattice volumes ($L^3$) calculated by $V(\vec{r})$ indicate that there is no bound state in the $ΞΞ(^1\mathrm{S}_0)$ channel at $m_π=0.51$ GeV in 2+1 flavor QCD.

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arXiv2013

A comparative study of two lattice approaches to two-body systems

We present a method to extract the spectrum of two-particle systems on the lattice from wave functions computed in lattice simulations. The energies of the Hamiltonian eigenstates are extracted from the eigenvalues of a matrix, similar to a potential, constrained by the wave functions. This method is compared with the traditional variational method in the isospin 2 $ππ$ system.

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arXiv2013

Equation of State of Nucleon Matters from Lattice QCD Simulations

Nucleon matters are studied based on QCD. We extract nucleon-nucleon interaction from lattice QCD simulations in a recently developed approach, and then derive the equations of state of the symmetric nuclear matter and the pure neutron matter, at zero temperature, in the Brueckner-Hartree-Fock framework. We find that QCD reproduce known features of the symmetric nuclear matter, such as the self-binding and saturation, at some values of quark mass. We find also that the pure neutron matter become more stiff at large density as quark mass decrease. We apply these equations of state to neutron star and study its mass and radius.

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arXiv2013

Cutoff effects on lattice nuclear forces

We present a lattice QCD study for the cutoff effects on nuclear forces. Two-nucleon forces are determined from Nambu-Bethe-Salpeter (NBS) wave functions using the HAL QCD method. Lattice QCD simulations are performed employing N_f = 2 clover fermion configurations at three lattice spacings of a = 0.108, 0.156, 0.215 fm on a fixed physical volume of L^3 x T = (2.5 fm)^3 x 5 fm with a large quark mass corresponding to m_π= 1.1 GeV. We observe that while the discretization artifact appears at the short range part of potentials, it is suppressed at the long distance region. The cutoff dependence of the phase shifts and scattering length is also presented.

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arXiv2012

Pion-pion interaction in the I=1 channel

We present preliminary results of a new approach to the study of the pion-pion system in the I=1 channel. The Bethe-Salpeter wave function of the two-pion system is computed on the ground state and the first excited state. From these, we attempt to extract an interaction kernel (potential) which can then be used to extract observables such as the phase shifts. In a first trial, we use rather large pion masses $m_π\sim 1.05$ GeV and $m_π\sim 0.68$ GeV which do not allow rho decay.

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arXiv2012

Study of H-dibaryon mass in Lattice QCD

After a brief review of discovery of the H-dibaryon in lattice QCD, effect of the flavor SU(3) symmetry breaking on the H-dibaryon is studied by basing on the baryon-baryon (BB) interactions extracted from QCD on the lattice. The Schrodinger equation for Lambda Lambda - N Xi -Sigma Sigma coupled-channel is solved with the physical baryon masses and the potentials obtained from QCD at the flavor SU(3) limit. A resonant H-dibaryon is found between Lambda Lambda and N Xi thresholds in this treatment.

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arXiv2012

Nuclear physics from lattice simulations

We review recent lattice QCD activities with emphasis on the impact on nuclear physics. In particular, the progress toward the determination of nuclear and baryonic forces (potentials) using Nambu-Bethe-Salpeter (NBS) wave functions is presented. We discuss major challenges for multi-baryon systems on the lattice: (i) signal to noise issue and (ii) computational cost issue. We argue that the former issue can be avoided by extracting energy-independent (non-local) potentials from time-dependent NBS wave functions without relying on the ground state saturation, and the latter cost is drastically reduced by developing a novel "unified contraction algorithm." The lattice QCD results for nuclear forces, hyperon forces and three-nucleon forces are presented, and physical insights are discussed. Comparison to results from the traditional Luescher's method is given, and open issues to be resolved are addressed as well.

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arXiv2012

Few-baryon interactions from lattice QCD

We report the recent progress on the determination of three-nucleon forces (3NF) in lattice QCD. We utilize the Nambu-Bethe-Salpeter (NBS) wave function to define the potential in quantum field theory, and extract two-nucleon forces (2NF) and 3NF on equal footing. The enormous computational cost for calculating multi-baryon correlators on the lattice is drastically reduced by developing a novel contraction algorithm (the unified contraction algorithm). Quantum numbers of the three-nucleon (3N) system are chosen to be (I, J^P)=(1/2,1/2^+) (the triton channel), and we extract 3NF in which three nucleons are aligned linearly with an equal spacing. Lattice QCD simulations are performed using N_f=2 dynamical clover fermion configurations at the lattice spacing of a = 0.156 fm on a 16^3 x 32 lattice with a large quark mass corresponding to m(π)= 1.13 GeV. Repulsive 3NF is found at short distance.

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arXiv2012

Baryon-baryon interaction of strangeness S=-1 sector

We present our recent studies on hyperon-nucleon (YN) interactions in the strangeness S=-1 that $pΛ, Σ^0 p$ and $Σ^+ n$, by extracting corresponding potentials through Nambu-Bethe-Salpeter wave functions. We calculate $ΛN$ and $ΣN$ potentials in the isospin I=3/2 channel, using the $N_f=2+1$ gauge configurations generated by PACS-CS collaboration and employing an improved method to obtain potentials in lattice QCD simulations. For the $^1S_0$ channel, the central $ΣN (I=3/2, ^1S_0)$ potential and the central $ΛN (^1S_0)$ potential are found to be very similar. In the spin triplet ($^3S_1-^3D_1$) channels, the central $ΛN(^3S_1-^3D_1)$ potential is attractive while the central $ΣN(I=3/2, ^3S_1-^3D_1)$ potentials is repulsive. Tensor potentials, on the other hand, are rather weak in the diagonal part of both $ΛN$ and $ΣN(I=3/2)$ systems.

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arXiv2012

Exploring Three-Nucleon Forces in Lattice QCD

Three-nucleon forces (3NF) are investigated from two-flavor lattice QCD simulations. We utilize the Nambu-Bethe-Salpeter (NBS) wave function to determine two-nucleon forces (2NF) and 3NF in the same framework. As a first exploratory study, we extract 3NF in which three nucleons are aligned linearly with an equal spacing. This is the simplest geometrical configuration which reduces the huge computational cost of calculating the NBS wave function. Quantum numbers of the three-nucleon system are chosen to be (I, J^P)=(1/2,1/2^+) (the triton channel). Lattice QCD simulations are performed using N_f=2 dynamical clover fermion configurations at the lattice spacing of a = 0.156 fm on a 16^3 x 32 lattice with a large quark mass corresponding to m_π= 1.13 GeV. We find repulsive 3NF at short distance in the triton channel. Several sources of systematic errors are also discussed.

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arXiv2011

Three-Nucleon Forces explored by Lattice QCD Simulations

We explore three-nucleon forces (3NF) from lattice QCD simulations. Utilizing the Nambu-Bethe-Salpeter (NBS) wave function, two-nucleon forces (2NF) and 3NF are determined on the same footing. Quantum numbers of the three-nucleon (3N) system are chosen to be (I, J^P)=(1/2,1/2^+) (the triton channel). The enormous computational cost is reduced by employing the simplest geometrical configuration, where 3N are aligned linearly with an equal spacing. We perform lattice QCD simulations using Nf=2 dynamical clover fermion configurations generated by CP-PACS Collaboration, at the lattice spacing of a = 0.156 fm on a 16^3 x 32 lattice with a large quark mass corresponding to m(π) = 1.13 GeV. Repulsive 3NF is found at short distance.

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