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T. Hatsuda

Publications and source records attributed to T. Hatsuda.

At least 37 records · Page 2Linked to original sources
arXiv2010

The order of the deconfinement phase transition in a heavy quark mass region

We study the quark mass dependence of the QCD phase transition by an effective potential defined through the distribution function of observables. As a test of the method, we study the first order deconfinement phase transition in the heavy quark mass limit and its fate at lighter quark masses. We confirm that the distribution function for the plaquette has two peaks indicating that the phase transition is of first order in the heavy quark limit. We then study the quark mass dependence of the distribution function by a reweighting method combined with the hopping parameter expansion. We find that the first order transition turns into a crossover as the quark mass decreases. We determine the critical point for the cases of $N_f$=1, 2, 3 and 2+1. We find that the probability distribution function provides us with a powerful tool to study the order of transitions.

hep-lat↗
arXiv2010

QCD thermodynamics at zero and finite densities with improved Wilson quarks

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.

hep-lat↗
arXiv2010

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

We study the equation of state at finite temperature and density in two-flavor QCD with the RG-improved gluon action and the clover-improved Wilson quark action on a $ 16^3 \times 4$ lattice. Along the lines of constant physics at $m_{\rm PS}/m_{\rm V} = 0.65$ and 0.80, we compute the second and forth derivatives of the grand canonical partition function with respect to the quark chemical potential $μ_q = (μ_u+μ_d)/2$ and the isospin chemical potential $μ_I = (μ_u-μ_d)/2$ at vanishing chemical potentials, and study the behaviors of thermodynamic quantities at finite $μ_q$ using these derivatives for the case $μ_I=0$. In particular, we study density fluctuations at none-zero temperature and density by calculating the quark number and isospin susceptibilities and their derivatives with respect to $μ_q$. To suppress statistical fluctuations, we also examine new techniques applicable at low densities. We find a large enhancement in the fluctuation of quark number when the density increased near the pseudo-critical temperature, suggesting a critical point at finite $μ_q$ 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-anti-quark pairs. The results suggest that, to the leading order of $μ_q$, the interaction between two quarks becomes stronger at finite densities, while that between quark and anti-quark becomes weaker.

hep-lat↗
arXiv2010

Electric and Magnetic Screening Masses at Finite Temperature from Generalized Polyakov-Line Correlations in Two-flavor Lattice QCD

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 ($\R$) and the charge conjugation ($\Ca$), 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, ratio of the two screening masses agrees with that obtained from the dimensionally-reduced effective field theory and the ${\cal N}=4$ supersymmetric Yang-Mills theory.

hep-lat↗
arXiv2010

Kaon-Nucleon potential from lattice QCD

We study the KN interactions in the I(J^π)=0(1/2^-) and 1(1/2^-) channels and associated exotic state Θ^+ from 2+1 flavor full lattice QCD simulation for relatively heavy quark mass corresponding to m_π=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.

hep-lat↗
arXiv2010

Energy dependence of nucleon-nucleon potentials in lattice QCD

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.

hep-lat↗
arXiv2009

Heavy-quark free energy at finite temperature with 2+1 flavors of improved Wilson quarks in fixed scale approach

The free energy between a static quark and an antiquark is studied by using the color-singlet Polyakov-line correlation at finite temperature. We perform simulations on $32^3 \times 12$, 10, 8, 6, 4 lattices in the high temperature phase with the RG-improved gluon action and 2+1 flavors of the clover-improved Wilson quark action. Since the simulations are based on the fixed scale approach that the temperature can be varied without changing the spatial volume and renormalization factor, it is possible to investigate temperature dependence of the heavy-quark free energy without any adjustment of the overall constant. We find that, the heavy-quark free energies at short distance converge to the heavy-quark potential evaluated from the Wilson-loop operator at zero temperature, in accordance with the expected insensitivity of short distance physics to the temperature. At long distance, the heavy-quark free energies approach to twice the single-quark free energies, implying that the interaction between heavy quarks is screened. The Debye screening mass obtained from the long range behavior of the heavy-quark free energy is compared with results of the thermal perturbation theory and those of $N_f=2$ and $N_f=0$ lattice simulations.

hep-lat↗
arXiv2009

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

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 Wilson-type quarks, we adopt the fixed scale approach, i.e. the temperature T is varied by N_t 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.

hep-lat↗
arXiv2009

Proper heavy-quark potential from a spectral decomposition of the thermal Wilson loop

We propose a non-perturbative and gauge invariant derivation of the static potential between a heavy-quark ($Q$) and an anti-quark ($\bar{Q}$) at finite temperature. This proper potential is defined through the spectral function (SPF) of the thermal Wilson loop and can be shown to satisfy the Schrödinger equation for the heavy $Q\bar{Q}$ pair in the thermal medium. In general, the proper potential has a real and an imaginary part,corresponding to the peak position and width of the SPF. The validity of using a Schrödinger equation for heavy $Q\bar{Q}$ can also be checked from the structure of the SPF. To test this idea, quenched QCD simulations on anisotropic lattices ($a_σ=4a_τ=0.039\rm fm$, $N^3_σ\times N_τ =20^2 \times (96-32)$) are performed. The real part of the proper potential below the deconfinement temperature ($T=0.78T_c$) exhibits the well known Coulombic and confining behavior. At ($T=2.33T_c$) we find that it coincides with the Debye screened potential obtained from Polyakov-line correlations in the color-singlet channel under Coulomb gauge fixing. The physical meaning of the spectral structure of the thermal Wilson loop and the use of the maximum entropy method (MEM) to extract the real and imaginary part of the proper potential are also discussed.

hep-lat↗
arXiv2009

Nuclear Forces from Lattice QCD

A method to extract nucleon-nucleon (NN) potentials from the Bethe-Salpeter amplitude in lattice QCD is presented. It is applied to the two nucleons on the lattice with quenched QCD simulations. By disentangling the mixing between the S-state 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, the quark mass dependence and the velocity dependence of the NN potential are analyzed. Preliminary result in (2+1)-flavor QCD simulations is also shown.

hep-lat↗
arXiv2009

Fixed scale approach to the equation of state on the lattice

We propose a fixed scale approach to calculate the equation of state (EOS) in lattice QCD. In this approach, the temperature T is varied by Nt at fixed lattice spacings. This enables us to reduce T=0 simulations which are required to provide basic data in finite temperature studies but are quite expensive in the conventional fixed-Nt approach. Since the conventional integral method to obtain the pressure is inapplicable at fixed scale, we introduce a new method, "T-integration method", to calculate pressure non-perturbatively. We test the fixed scale approach armed with the T-integral method in quenched QCD on isotropic and anisotropic lattices. Our method is found to be powerful to obtain reliable results for the equation of state, especially at intermediate and low temperatures. Reduction of the computational cost of T=0 simulations is indispensable to study EOS in QCD with dynamical quarks. The status of our study in Nf=2+1 QCD with improved Wilson quarks is also reported.

hep-lat↗
arXiv2009

Free energies of heavy quarks in full-QCD lattice simulations with Wilson-type quark action

The free energy between a static quark and an antiquark is studied by using the color-singlet Polyakov-line correlation at finite temperature in lattice QCD with 2+1 flavors of improved Wilson quarks. From the simulations on $32^3 \times 12$, 10, 8, 6, 4 lattices in the high temperature phase, based on the fixed scale approach, we find that, the heavy-quark free energies at short distance converge to the heavy-quark potential evaluated from the Wilson loop at zero temperature, in accordance with the expected insensitivity of short distance physics to the temperature. At long distance, the heavy-quark free energies approach to twice the single-quark free energies, implying that the interaction between heavy quarks is screened. The Debye screening mass obtained from the long range behavior of the free energy is compared with the results of thermal perturbation theory.

hep-lat↗
arXiv2009

Nuclear forces from quenched and 2+1 flavor lattice QCD using the PACS-CS gauge configurations

Two of recent progress in lattice QCD approach to nuclear force are reported. (i) Tensor force from quenched lattice QCD: By truncating the derivative expansion of inter-nucleon potential to the strictly local terms, we obtain central force V_C(r) and tensor force V_T(r) separately from s-wave and d-wave components of Bethe-Salpeter wave function for two nucleon state with J^P=1^+. Numerical calculation is performed with quenched QCD on 32^4 lattice using the standard plaquette action at beta=5.7 with the standard Wilson quark action with kappa=0.1640, 0.1665, 0.1678. Preliminary results show that the depths of the resulting tensor force amount to 20 to 40 MeV, which is enhanced in the light quark mass region. (ii) Nuclear force from 2+1 flavor QCD with PACS-CS gauge configuration: Preliminary full QCD results are obtained by using 2+1 flavor gauge configurations generated by PACS-CS collaboration. The resulting potential has the midium range attraction of about 30 MeV similar to the preceding quenched calculations. However, the repulsive core at short distance is significantly stronger than the corresponding quenched QCD result.

hep-lat↗
arXiv2009

Fixed Scale Approach to Equation of State in Lattice QCD

A new approach to study the equation of state in finite-temperature QCD is proposed on the lattice. Unlike the conventional method in which the temporal lattice size $N_t$ is fixed, the temperature $T$ is varied by changing $N_t$ at fixed lattice scale. The pressure of the hot QCD plasma is calculated by the integration of the trace anomaly with respect to $T$ at fixed lattice scale. This "$T$-integral method" is tested in quenched QCD on isotropic and anisotropic lattices and is shown to give reliable results especially at intermediate and low temperatures.

hep-lat↗
arXiv2009

Lambda-nucleon force from lattice QCD

We study the $Λ$-nucleon ($ΛN$) force by using lattice QCD. The Bethe-Salpeter amplitude is calculated for the lowest scattering state of the $ΛN$ so as to obtain the $ΛN$ potential. The numerical calculation is twofold: (i) Full lattice QCD by using 2+1 flavor PACS-CS gauge configurations with, $β=1.9$, corresponding to the lattice spacing of $a=0.0907(13)$ fm, on a $32^3\times 64$ lattice. A set of parameter $(κ_{ud},κ_s)=(0.13770,0.13640)$ is used, which corresponds to $m_π\approx 300$ MeV and $m_K\approx 594$ MeV. The spatial lattice volume corresponds to (2.86 fm)$^3$. (ii) Quenched lattice QCD with $β=5.7$, the lattice spacing of $a=0.1416(9)$ fm, on the $32^3\times48$ lattice. Two sets of hopping parameters $(κ_{ud},κ_s)=(0.1665,0.1643),(0.1670,0.1643)$ are used. The spatial lattice volume is (4.5 fm)$^3$. For the full QCD, we find that the $Λp$ has a relatively strong (weak) repulsive core in the $^1S_0$ ($^3S_1$) channel at short distance, while the potential has slight attractive region at medium distance. The lowest scattering energy in the finite lattice volume is calculated; Slightly negative values obtained in both spin channels. For the quenched QCD, we find that the results are qualitatively in agreement with those in the full QCD calculation.

hep-lat↗
arXiv2009

Hyperon-nucleon force from lattice QCD

We calculate potentials between a proton and a $Ξ^0$ (hyperon with strangeness -2) through the equal-time Bethe-Salpeter wave function, employing quenched lattice QCD simulations with the plaquette gauge action and the Wilson quark action on (4.5 fm)^4 lattice at the lattice spacing $a \simeq 0.14$ fm. The ud quark mass in our study corresponds to $m_π\simeq 0.37$ and 0.51 GeV, while the s quark mass corresponds to the physical value of $m_K$. The central $p Ξ^0$ potential has a strong (weak) repulsive core in the $^1S_0$ ($^3S_1$) channel for $r \lsim 0.6$ fm, while the potential has attractive well at the medium and long distances (0.6 fm $\lsim r \lsim 1.2$ fm) in both channels. The sign of the $p Ξ^0$ scattering length and its quark mass dependence indicate a net attraction in both channels at low energies.

nucl-th↗
arXiv2008

Magnetic and electric screening masses from Polyakov-loop correlations

Screening properties of the quark gluon plasma are studied from Polyakov-loop correlation in lattice QCD simulations with two flavors of improved Wilson quarks at temperatures $T/\Tpc \simeq 1$--4 where $\Tpc$ is the pseudocritical temperature. Using the Euclidean-time reflection symmetry and the charge conjugation symmetry, we introduce various types of Polyakov-loop correlation functions and extract screening masses in magnetic and electric sectors. We find that the temperature dependence of the screening masses are well described by the weak coupling expansion. We also find that a ratio of the screening masses in the electric sector to the magnetic sector shows qualitative agreement with a prediction from the dimensionally-reduced effective field theory and the N=4 supersymmetric Yang-Mills theory at $1.3 < T/\Tpc < 3$.

hep-lat↗