Showing papers by "Noriyoshi Ishii published in 2010"

Theoretical Foundation of the Nuclear Force in QCD and Its Applications to Central and Tensor Forces in Quenched Lattice QCD Simulations

Abstract: We present full accounts of a method to extract nucleon-nucleon ( NN ) potentials from the Bethe-Salpter amplitude in lattice QCD. The method is applied to two nucleons on the lattice with quenched QCD simulations. By disentangling the mixing between the Sstate and the D-state, we obtain central and tensor potentials in the leading order of the velocity expansion of the non-local NN potential. The spatial structure and the quark mass dependence of the potentials are analyzed in detail. Subject Index: 164, 232, 234

Baryon-Baryon Interactions in the Flavor SU(3) Limit from Full QCD Simulations on the Lattice

Abstract: We investigate baryon-baryon (BB) interactions in the 3-flavor full QCD simulations with degenerate quark masses for all flavors. The BB potentials in the orbital S-wave are extracted from the Nambu-Bethe-Salpeter wave functions measured on the lattice. We observe strong flavor-spin dependences of the BB potentials at short distances. In particular, a strong repulsive core exists in the flavor-octet and spin-singlet channel (the 8_s representation), while an attractive core appears in the flavor singlet channel (the 1 representation). We discuss a relation of such flavor-spin dependence with the Pauli exclusion principle in the quark level. Possible existence of an H-dibaryon resonance above the Lambda-Lambda threshold is also discussed.

Baryon-Baryon Interactions in the Flavor SU(3) Limit from Full QCD Simulations on the Lattice

Abstract: We investigate baryon-baryon (BB) interactions in the 3-flavor full QCD simulations with degenerate quark masses for all flavors. The BB potentials in the orbital S-wave are extracted from the Nambu-Bethe-Salpeter wave functions measured on the lattice. We observe strong flavor-spin dependences of the BB potentials at short distances. In particular, a strong repulsive core exists in the flavor-octet and spin-singlet channel (the 8s representation), while an attractive core appears in the flavor singlet channel (the 1 representation). We discuss the relation of such flavor-spin dependence with the Pauli exclusion principle at the quark level. The possible existence of an H-dibaryon resonance above the ΛΛ threshold is also discussed. Subject Index: 164, 234

Equation of State and Heavy-Quark Free Energy at Finite Temperature and Density in Two Flavor Lattice QCD with Wilson Quark Action

Abstract: We study the equation of state at finite temperature and density in two-flavor QCD with the renormalization group improved gluon action and the clover-improved Wilson quark action on a ${16}^{3}\ifmmode\times\else\texttimes\fi{}4$ lattice. Along the lines of constant physics at ${m}_{\mathrm{PS}}/{m}_{\mathrm{V}}=0.65$ and 0.80, we compute the second and forth derivatives of the grand canonical partition function with respect to the quark chemical potential ${\ensuremath{\mu}}_{q}=({\ensuremath{\mu}}_{u}+{\ensuremath{\mu}}_{d})/2$ and the isospin chemical potential ${\ensuremath{\mu}}_{I}=({\ensuremath{\mu}}_{u}\ensuremath{-}{\ensuremath{\mu}}_{d})/2$ at vanishing chemical potentials, and study the behaviors of thermodynamic quantities at finite ${\ensuremath{\mu}}_{q}$ using these derivatives for the case ${\ensuremath{\mu}}_{I}=0$. In particular, we study density fluctuations at nonezero temperature and density by calculating the quark number and isospin susceptibilities and their derivatives with respect to ${\ensuremath{\mu}}_{q}$. To suppress statistical fluctuations, we also examine new techniques applicable at low densities. We find a large enhancement in the fluctuation of the quark number when the density increased near the pseudocritical temperature, suggesting a critical point at finite ${\ensuremath{\mu}}_{q}$ terminating the first order transition line between hadronic and quark-gluon-plasma phases. This result agrees with the previous results using staggered-type quark actions qualitatively. Furthermore, we study heavy-quark free energies and Debye screening masses at finite density by measuring the first and second derivatives of these quantities for various color channels of heavy quark-quark and quark-antiquark pairs. The results suggest that, to the leading order of ${\ensuremath{\mu}}_{q}$, the interaction between two quarks becomes stronger at finite densities, while that between quark and antiquark becomes weaker.

Electric and magnetic screening masses at finite temperature from generalized Polyakov-line correlations in two-flavor lattice QCD

Abstract: Screenings of the quark-gluon plasma in electric and magnetic sectors are studied on the basis of generalized Polyakov-line correlation functions in lattice QCD simulations with two flavors of improved Wilson quarks. Using the Euclidean-time reflection ($\mathcal{R}$) and the charge conjugation ($\mathcal{C}$), electric and magnetic screening masses are extracted in a gauge-invariant manner. Long distance behavior of the standard Polyakov-line correlation in the quark-gluon plasma is found to be dictated by the magnetic screening. Also, the ratio of the two screening masses agrees with that obtained from the dimensionally-reduced effective field theory and the $\mathcal{N}=4$ supersymmetric Yang-Mills theory.

Kaon-Nucleon potential from lattice QCD

Abstract: We study the KN interactions in the I(J^{\pi})=0(1/2^-) and 1(1/2^-) channels and associated exotic state \Theta^+ from 2+1 flavor full lattice QCD simulation for relatively heavy quark mass corresponding to m_{\pi}=871 MeV. The s-wave KN potentials are obtained from the Bethe-Salpeter wave function by using the method recently developed by HAL QCD (Hadrons to Atomic nuclei from Lattice QCD) Collaboration. Potentials in both channels reveal short range repulsions: Strength of the repulsion is stronger in the I=1 potential, which is consistent with the prediction of the Tomozawa-Weinberg term. The I=0 potential is found to have attractive well at mid range. From these potentials, the $KN$ scattering phase shifts are calculated and compared with the experimental data.

Energy dependence of nucleon-nucleon potentials in lattice QCD

Abstract: Recently a new approach to calculate the nuclear potential from lattice QCD has been proposed. In the approach the nuclear potential is constructed from Bethe-Salpeter (BS) wave functons through the Schroedinger equation. The procedure leads to non-local but energy independent potential, which can be expanded in terms of local functions. In several recent applications of this method, local potentials, which correspond to the leading order (LO) terms of the expansion, are calculated from the BS wave function at E ' 0 MeV, where E is the center of mass energy. It is therefore important to check the validity of the LO approximation obtained at E ' 0. In this report, in order to check how well the LO approximation for the NN potentials works, we compare the LO potentials determined from the BS wave function at E ' 45 MeV with those at E ' 0 MeV in quenched QCD. We find that the difference of the LO potentials between two energies are not found wihin the statistical errors. This shows that the LO approximation for the potential is valid at low energies to describe the NN interactions.

non-locality of the nucleon-nucleon potential from Lattice QCD

Abstract: The Nambu-Bethe-Salpeter (NBS) wave function for two nucleons on the lattice has been shown to yield a non-local and energy-independent nucleon-nucleon (NN) potential, U(~r,~r′). In practice, the derivative expansion of U(~r,~r′) is currently employed to determine the potential at low energies. In this report, we study the magnitude of non-locality to check the convergence of such a derivative expansion. With quenched lattice QCD at mπ = 530MeV, we compare the NN potentials at the center of mass energy E ' 0 MeV and at E ' 45 MeV. We also investigate the angular momentum dependence of the spin singlet potential, by comparing the potentials in S0 and D2 channels. We find that the non-locality and the angular momentum dependence in the above energy range are negligible within statistical errors.

Non-locality of the nucleon-nucleon potential from Lattice QCD

Abstract: The Nambu-Bethe-Salpeter (NBS) wave function for two nucleons on the lattice has been shown to yield a non-local and energy-independent nucleon-nucleon (NN) potential, U(r,r'). In practice, the derivative expansion of U(r,r') is currently employed to determine the potential at low energies. In this report, we study the magnitude of non-locality to check the convergence of such a derivative expansion. With quenched lattice QCD at m_\pi = 530MeV, we compare the NN potentials at the center of mass energy E ~ 0 MeV and at E ~ 45 MeV. We also investigate the angular momentum dependence of the spin singlet potential, by comparing the potentials in 1S0 and 1D2 channels. We find that the non-locality and the angular momentum dependence in the above energy range are negligible within statistical errors.

Energy dependence of nucleon-nucleon potentials in lattice QCD

Abstract: Recently a new approach to calculate the nuclear potential from lattice QCD has been proposed. In the approach the nuclear potential is constructed from Bethe-Salpeter (BS) wave functons through the Schroedinger equation. The procedure leads to non-local but energy independent potential, which can be expanded in terms of local functions. In several recent applications of this method, local potentials, which correspond to the leading order (LO) terms of the expansion, are calculated from the BS wave function at E~0 MeV, where E is the center of mass energy. It is therefore important to check the validity of the LO approximation obtained at E~0. In this report, in order to check how well the LO approximation for the NN potentials works, we compare the LO potentials determined from the BS wave function at E~45 MeV with those at E~0 MeV in quenched QCD. We find that the difference of the LO potentials between two energies are not found wihin the statistical errors. This shows that the LO approximation for the potential is valid at low energies to describe the NN interactions.

Lattice study of nuclear forces

Abstract: Recent progress of lattice QCD study of nuclear forces (potentials) is reviewed. Scattering phase shift is an important observable for two particle system. In lattice QCD, phase shifts are calculated from long distance behavior of Bethe-Salpeter (BS) wave functions by Luescher's finite volume method. For applications to nuclear physics of multi-nucleon system, it is more advantageous to convert the information of phase shifts in the form of potentials. We therefore extend the method so as to generate the potentials from BS wave functions. These potentials are faithful to scattering phase shift by construction, because they can reproduce BS wave functions in which the information of phase shift is embeded in the long distance part.The method was first applied to the central potential in NN system. It is now applied to many objects, such as tensor potential, hyperon potentials, energy dependence of nuclear potentials, and investigations of the repulsive core at short distance.

A Faceted-Navigation System for QCDml Ensemble XML Data

Abstract: In this paper we describe a faceted navigation system for QCDml ensemble XML data, which is an XML-based metadata format for ILDG (International Lattice Data Grid). A faceted navigation system allows a user to search for one's desired information in an exploratory way, thereby enabling the user to browse a set of XML data without using specialized query languages such as XPath and XQuery. However, designing a faceted navigation interface for XML data is not straightforward due to the tree and flexible, tree-like nature of XML. In this work, we attempt to design and implement a dedicated faceted navigation system for QCDml on top of an XML database. The interface is designed by taking the domain experts' usability into account. We also care about the system's performance. In general, the process of faceted navigation is computationally expensive because of the need for aggregate computation of each available facets. In order to alleviate this, we make use of a relational database system as the engine to speed up the aggregate computation. We finally demonstrate the implemented faceted navigation system, which has been made available on the Web.

Lattice study of nuclear forces

Abstract: Recent progress of lattice QCD study of nuclear forces (potentials) is reviewed. Scattering phase shift is an important observable for two particle system. In lattice QCD, phase shifts are calculated from long distance behavior of Bethe-Salpeter (BS) wave functions by Luescher's finite volume method. For applications to nuclear physics of multi-nucleon system, it is more advantageous to convert the information of phase shifts in the form of potentials. We therefore extend the method so as to generate the potentials from BS wave functions. These potentials are faithful to scattering phase shift by construction, because they can reproduce BS wave functions in which the information of phase shift is embeded in the long distance part.The method was first applied to the central potential in NN system. It is now applied to many objects, such as tensor potential, hyperon potentials, energy dependence of nuclear potentials, and investigations of the repulsive core at short distance.

Towards the equation of state in 2+1 flavor QCD with improved Wilson quarks in the fixed scale approach

Abstract: We report on the status of our study towards the equation of state in 2 + 1 flavor QCD with improved Wilson quarks. To reduce the computational cost which is quite demanding for Wilsontype quarks, we adopt the fixed scale approach, i.e. the temperature T is varied by Nt at fixed lattice spacing. Since the conventional integral method to obtain the pressure is inapplicable at a fixed scale, we adopt the "T-integral method", to calculate the pressure non-perturbatively. Reduction of the computational cost of T = 0 simulations thus achieved is indispensable to study EOS in QCD with dynamical quarks.

Kaon-Nucleon potential from lattice QCD

Abstract: We study the KN interactions in the I(J � ) = 0(1/2 − ) and 1(1/2 − ) channels and associated exotic state � + from 2+1 f avor full lattice QCD simulation for relatively heavy quark mass corresponding to m� = 871 MeV. The s-wave KN potentials are obtained from the Bethe-Salpeter wave function by using the method recently developed by HAL QCD (Hadrons to Atomic nuclei from Lattice QCD) Collaboration. Potentials in both channels reveal short range repulsions: Strength of the repulsion is stronger in the I = 1 potential, which is consistent with the prediction of the Tomozawa-Weinberg term. The I = 0 potential is found to have attractive well at mid range. From these potentials, the KN scattering phase shifts are calculated and compared with the experimental data.

QCD Thermodynamics at Zero and Finite Densities with Improved Wilson Quarks

Abstract: The WHOT-QCD Collaboration is pushing forward lattice studies of QCD at finite temperatures and densities using improved Wilson quarks. We first present results on QCD at zero and finite densities with two flavors of degenerate quarks (N_F=2 QCD) adopting the conventional fixed-Nt approach. We then report on the status of a study of N_F=2+1 QCD adopting a fixed-scale approach armed with the T-integration method which we have developed.

Study of hyperon-nucleon potential from lattice QCD

Abstract: We study pΞ0 and pΛ forces by using quenched lattice QCD. The Bethe-Salpeter amplitude is calculated for the lowest scattering state of the systems. The numerical calculation is twofold: (i) For the pΞ0, the potentials and scattering lengths are obtained by using 323 × 32 lattice with β = 5.7, the lattice spacing of a = 0.1416(9) fm, and two kinds of ud quark mass corresponding to mπ ≃ 0.37 GeV and 0.51 GeV. The present results indicate that the pΞ0 interactions are both attractive at 1S0 and 3S1 channels, and the interaction in the 3S1 is more attractive than in the 1S0. These attractive forces become stronger as the u, d quark mass decreases. (ii) For the pΛ, the potentials are calculated by using the 323 × 48 lattice, and two kinds of ud quark mass corresponding to mπ ≃ 0.47 GeV and 0.51 GeV. The present preliminary result shows that the pΛ interactions are both attractive at 1S0 and 3S1 channels.

QCD thermodynamics at zero and finite densities with improved Wilson quarks

Abstract: The WHOT-QCD Collaboration is pushing forward lattice studies of QCD at finite temperatures and densities using improved Wilson quarks. We first present results on QCD at zero and finite densities with two flavors of degenerate quarks (N_F=2 QCD) adopting the conventional fixed-Nt approach. We then report on the status of a study of N_F=2+1 QCD adopting a fixed-scale approach armed with the T-integration method which we have developed.