Search

The spectrum of the negative-parity spin-1/2 $\Lambda$ baryons is studied using lattice QCD and hadronic effective theory in a unitarized coupled-channel framework. A direct comparison between the two approaches is possible by considering the hadronic effective theory in a finite volume and with hadron masses and mesonic decay constants that correspond to the situation studied on the lattice. Comparing the energy level spectrum and $SU(3)$ flavor decompositions of the individual states, it is found that the lowest two states extracted from lattice QCD can be identified with one of the two $\Lambda(1405)$-poles and the $\Lambda(1670)$ resonance. The quark mass dependences of these two lattice QCD levels are in good agreement with their effective theory counterparts. However, as current lattice QCD studies still rely on three-quark operators to generate the physical states, clear signals corresponding to the meson-baryon scattering states, that appear in the finite volume effective theory calculation, are not yet seen., Comment: 10 pages, 6 figures

We present four-body calculations of double-heavy tetraquarks in quark model. Several bound states are found for various flavor combinations. One of them is a strongly bound $$bb {\bar{q}} {\bar{q}}$$ with isospin and spin-parity $$I(J^P) = 0(1^+)$$ , having a binding energy of almost 200 MeV. This is consistent with the predictions of lattice QCD. We have also found a shallow state for the same $$I(J^P) = 0(1^+)$$ channel. By computing density distributions, it is shown that the deep one is a compact tetraquark state, while the shallow one is regarded as a loosely-bound molecule of two color singlet mesons, B and $$B^*$$ . This is a hadronic analogue of the cluster formation in light nuclei, the first example that hadrons with totally different nature emerge from a single Hamiltonian.

Real-time evolution of replicas of classical fields is proposed as an approximate simulator of real-time quantum field dynamics at finite temperatures. We consider $N$ classical field configurations, $(\phi_{{\tau{\boldsymbol{x}}}},\pi_{{\tau{\boldsymbol{x}}}}) (\tau=0,1,\ldots, N-1)$, dubbed as replicas, which interact with each other via $\tau$-derivative terms and evolve with the classical equation of motion. The partition function of replicas is found to be proportional to that of a quantum field in the imaginary-time formalism. Since the replica index can be regarded as the imaginary-time index, replica evolution is technically the same as the molecular dynamics part of hybrid Monte Carlo sampling. Then the replica configurations should reproduce the correct quantum equilibrium distribution after long time evolution. At the same time, evolution of the replica-index average of field variables is described by the classical equation of motion when the fluctuations are small. In order to examine the real-time propagation properties of replicas, we first discuss replica evolution in quantum mechanics. Statistical averages of observables are precisely obtained by the initial condition average of replica evolution, and the time evolution of the unequal-time correlation function, $\langle x(t) x(t')\rangle$, in a harmonic oscillator is also described well by the replica evolution in the range $T/\omega > 0.5$. Next, we examine the statistical and dynamical properties of the $\phi^4$ theory in 4+1D spacetime, which contains three spatial, one replica index or imaginary time, and one real time. We note that the Rayleigh–Jeans divergence can be removed in replica evolution with $N \geq 2$ when the mass counterterm is taken into account. We also find that the thermal mass obtained from the unequal-time correlation function at zero momentum grows as a function of the coupling as in the perturbative estimate in the small coupling region.

Bound states of double-heavy tetraquarks are studied in a constituent quark model. Two bound states are found for isospin and spin-parity I(JP)=0(1+) in the bbu¯d¯ channel. One is deeply bound and compact made of colored diquarks, while the other is shallow and extended as a BB⁎ molecule. The former agrees well with lattice QCD results. A systematic decrease in the binding energy is seen by replacing one of the heavy quarks to a lighter one. Altogether we find ten bound states. It is shown for the first time that hadrons with totally different natures emerge from a single Hamiltonian.

We calculate the low-lying spectrum of charmed baryons in lattice QCD on the $32^3\times64$, $N_f=2+1$ PACS-CS gauge configurations at the almost physical pion mass of $\sim 156$ MeV/c$^2$. By employing a set of interpolating operators with different Dirac structures and quark-field smearings for the variational analysis, we extract the ground and first few excited states of the spin-$1/2$ and spin-$3/2$, singly-, doubly-, and triply-charmed baryons. Additionally, we study the $\Xi_c$-$\Xi_c^\prime$ mixing and the operator dependence of the excited states in a variational approach. We identify several states that lie close to the experimentally observed excited states of the $\Sigma_c$, $\Xi_c$ and $\Omega_c$ baryons, including some of the $\Xi_c$ states recently reported by LHCb. Our results for the doubly- and triply-charmed baryons are suggestive for future experiments., Comment: 17 pages, 8 figures. version published in PRD

We investigate the shear viscosity of massless classical scalar fields in the $\phi^4$ theory on a lattice by using the Green–Kubo formula. Based on the scaling property of the classical field, the shear viscosity is represented using a scaling function. The equilibrium expectation value of the time-correlation function of the energy–momentum tensor is evaluated as the ensemble average of the classical field configurations, whose time evolution is obtained by solving the classical equation of motion starting from the initial condition in thermal equilibrium. It is found that there are two distinct damping time scales in the time-correlation function, which is found to show damped oscillation behavior in the early stage around a slow monotonic decay with an exponential form, and the slow decay part is found to dominate the shear viscosity in the massless classical field theory. This kind of slow decay is also known to exist in molecular dynamics simulations, so it may be a generic feature of dense matter.

With the aim of clarification of color correlations among quarks, we investigate the color correlation between a static quark and an antiquark (static $q\bar q$) below and above the phase transition temperature $T_c$ through the entanglement entropy(EE). By a quenched lattice QCD calculation on an anisotropic lattice adopting the standard Wilson gauge action in the Coulomb gauge, we compute a reduced density matrix $\rho$ defined in the color space, and the entanglement entropy $S_{\rm EE}$ constructed from $\rho$. The spatial volume is $L^3 = 24^3$ and the temporal extents are $N_T = 12,13,14,15,16,18,20$ and $24$, with a gauge coupling $\beta = 5.75$ and a renormalized anisotropy $\xi = 4.0$, which corresponds to temperatures between 180 and 370 MeV. From an analysis of $\rho$ and $S_{\rm EE}$, the color correlation between $q\bar q$ pairs is obtained as a function of the interquark distance $R$ and the temperature $T$. Below $T_c$, the $R$-dependence of the color correlation resembles that at $T=0$: the quark's color correlation gradually decreases as $R$ increases due to the color screening by in-between gluons. Above $T_c$, due to the deconfinement phase transition, the color correlation among quarks is found to quickly dissappear. Further, we investigate the color screening effect via the screening mass defined by $\rho$, and discuss the differences in the screening properties between the small and large R regions., Comment: 8 pages, 4 figures

We investigate the shear viscosity $\eta$ of the classical Yang-Mills (CYM) field on a lattice by using the Green-Kubo formula, where the shear viscosity is calculated from the time-correlation function of the energy-momentum tensor in equilibrium. Dependence of the shear viscosity $\eta(g,T)$ on the coupling $g$ and temperature $T$ is represented by a scaling function $f_\eta(g^2T)$ as $\eta(g,T)=Tf_\eta(g^2T)$ due to the scaling-invariant property of the CYM. The explicit functional form of $f_\eta(g^2T)$ is successfully determined from the calculated shear viscosity: It turns out that $\eta(g,T)$ of the CYM field is proportional to $1/g^{1.10-1.88}$ at weak coupling, which is a weaker dependence on $g$ than that in the leading-order perturbation theory but consistent with that of the "anomalous viscosity" $\eta\propto 1/g^{1.5}$ under the strong disordered field. The obtained shear viscosity is also found to be roughly consistent with that estimated through the analysis of the anisotropy of the pressure of the CYM dynamics in the expanding geometry with recourse to a hydrodynamic equation., Comment: 10pages, 11figures

We evaluate the electromagnetic Ξ c γ → Ξ c ′ transition on 2+1 flavor lattices corresponding to a pion mass of ∼ 156 MeV . We extract the magnetic Sachs and Pauli form factors which give the Ξ c – Ξ c ′ transition magnetic moment and the decay widths of Ξ c ′ baryons. We did not find a signal for the magnetic form factor of the neutral transition Ξ c 0 γ → Ξ c ′ 0 , which is suppressed by the U-spin flavor symmetry. As a byproduct, we extract the magnetic form factors and the magnetic moments of Ξ c and Ξ c ′ baryons, which give an insight to the dynamics of u / d , s and c quarks having masses at different scales.

We evaluate the ΛcΣcπ coupling constant ( GΛcΣcπ ) and the width of the strong decay Σc→Λcπ in 2+1 flavor lattice QCD on four different ensembles with pion masses ranging from 700 MeV to 300 MeV. We find GΛcΣcπ=18.332(1.476)stat.(2.171)syst. and the decay width Γ(Σc→Λcπ)=1.65(28)stat.(30)syst. MeV on the physical quark-mass point, which is in agreement with the recent experimental determination.

We study the color correlation between static quark and antiquark ($q\bar q$) in the confined phase via reduced density matrices $\rho$ defined in color space. We adopt the standard Wilson gauge action and perform quenched calculations with the Coulomb gauge condition for reduced density matrices. The spatial volumes are $L^3 = 8^3$, $16^3$, $32^3$ and $48^3$, with the gauge couplings $\beta = 5.7$, 5.8 and 6.0. Each element of the reduced density matrix in the sub space of quarks' color degrees of freedom of the $q\bar q$ pair is calculated from staples defined by link variables. As a result, we find that $\rho$ is well written by a linear combination of the strongly correlated $q\bar q$ pair state with the color-singlet component and the uncorrelated $q\bar q$ pair state with random color configurations. We compute the Renyi entropies $S^{\rm Renyi}$ from $\rho$ to investigate the $q\bar q$ distance dependence of the color correlation of the $q\bar q$ pair and find that the color correlation is quenched as the distance increases., Comment: 10 pages, 15 figures

Motivated by the recent experimental discoveries of multi-quark candidates, e.g., the $\Theta^+(1540)$, we study multi-quark systems in lattice QCD. First, we perform accurate mass measurements of low-lying 5Q states with $J=1/2$ and I=0 in both positive- and negative-parity channels in anisotropic lattice QCD. The lowest positive-parity 5Q state is found to have a large mass of about 2.24GeV after the chiral extrapolation. To single out the compact 5Q state from $NK$ scattering states, we develop a new method with the hybrid-boundary condition (HBC), and find no evidence of the compact 5Q state below 1.75GeV in the negative-parity channel. Second, we perform the first study of the multi-quark potential in lattice QCD to clarify the inter-quark interaction in multi-quark systems. The 5Q potential $V_{\rm 5Q}$ for the QQ-${\rm \bar{Q}}$-QQ system is found to be well described by the ``OGE Coulomb plus multi-Y Ansatz": the sum of the one-gluon-exchange (OGE) Coulomb term and the multi-Y-type linear term based on the flux-tube picture. The 4Q potential $V_{\rm 4Q}$ for the QQ-${\rm \bar{Q}\bar{Q}}$ system is also described by the OGE Coulomb plus multi-Y Ansatz, when QQ and $\rm \bar Q \bar Q$ are well separated. The 4Q system is described as a "two-meson" state with disconnected flux tubes, when the nearest quark and antiquark pair is spatially close. We observe a lattice-QCD evidence for the ``flip-flop'', i.e., the flux-tube recombination between the connected 4Q state and the ``two-meson'' state. On the confinement mechanism, the lattice QCD results indicate the flux-tube-type linear confinement in multi-quark hadrons., Comment: 22 pages, 3 tables, 16 figures. Talk given at International Workshop on Quark Nuclear Physics 2005 (QNP05), Phoenix Park, Korea, 22-24, Feb., 2005

We evaluate the spin-$3/2 \to$ spin-$1/2$ electromagnetic transitions of the doubly charmed baryons on 2+1 flavor, $32^3 \times 64$ PACS-CS lattices with a pion mass of $156(9)$ MeV/c$^2$. A relativistic heavy quark action is employed to minimize the associated systematic errors on charm-quark observables. We extract the magnetic dipole, $M1$, and the electric quadrupole, $E2$, transition form factors. In order to make a reliable estimate of the $M1$ form factor, we carry out an analysis by including the effect of excited-state contributions. We find that the $M1$ transition is dominant and light degrees of freedom ($u/d$- or $s$-quark) play the leading role. $E2$ form factors, on the other hand, are found to be negligibly small, which in turn, have minimal effect on the helicity and transition amplitudes. We predict the decay widths and lifetimes of $\Xi_{cc}^{\ast +,++}$ and $\Omega_{cc}^{\ast +}$ based on our results. Finite size effects on these ensembles are expected to be around 1\%. Differences in kinematical and dynamical factors with respect to the $N\gamma\to\Delta$ transition are discussed and compared to non-lattice determinations as well keeping possible systematic artifacts in mind. A comparison to $\Omega_c \gamma \rightarrow \Omega_c^\ast$ transition and a discussion on systematic errors related to the choice of heavy quark action are also given. Results we present here are particularly suggestive for experimental facilities such as LHCb, PANDA, Belle II and BESIII to search for further states., Comment: 16 pages, 7 figures. Includes an improved analysis, a detailed comparison to model calculations and a systematic-error check between two actions for the charm quark observables. Version to appear in PRD

We investigate the thermalization process from a glasma-like initial condition in a static box in terms of the Husimi–Wehrl (HW) entropy defined with the Husimi function, a quantum distribution function in a phase space. We calculate the semiclassical time evolution of the HW entropy in Yang–Mills field theory with the phenomenological initial field configuration given by mimicking the McLerran–Venugopalan model in a static box, which has instability triggered by initial field fluctuations. Husimi–Wehrl entropy production implies the thermalization of the system and it reflects the underlying dynamics such as chaoticity and instability. By comparing the production rate with the Kolmogorov–Sinaï rate, we find that the HW entropy production rate is significantly larger than that expected from chaoticity. We also show that the HW entropy is finally saturated when the system reaches a quasi-stationary state. The saturation time of the HW entropy is comparable with that of pressure isotropization, which is around 1 fm/ in the present calculation.

We study $\Lambda$ baryons of spin-parity $\frac{1}{2}^{\pm}$ with either a strange or charm valence quark in full 2+1 flavor lattice QCD. Multiple $SU(3)$ singlet and octet operators are employed to generate the desired single baryon states on the lattice. Via the variational method, the couplings of these states to the different operators provide information about the flavor structure of the $\Lambda$ baryons. We make use of the gauge configurations of the PACS-CS Collaboration and chirally extrapolate the results for the masses and $SU(3)$ flavor components to the physical point. We furthermore gradually change the hopping parameter of the heaviest quark from strange to charm to study how the properties of the $\Lambda$ baryons evolve as a function of the heavy quark mass. It is found that the baryon energy levels increase almost linearly with the quark mass. Meanwhile, the flavor structure of most of the states remains stable, with the exception of the lowest $\frac{1}{2}^{-}$ state, which changes from a flavor singlet $\Lambda$ to a $\Lambda_c$ state with singlet and octet components of comparable size. Finally, we discuss whether our findings can be interpreted with the help of a simple quark model and find that the negative-parity $\Lambda_c$ states can be naturally explained as diquark excitations of the light $u$ and $d$ quarks. On the other hand, the quark-model picture does not appear to be adequate for the negative-parity $\Lambda$ states, suggesting the importance of other degrees of freedom to describe them., Comment: 14 pages, 8 figures, 5 tables; v2 (published version in PRD): title slightly changed, discussion about systematic uncertainties extended, typos fixed, references added

Using the axial-vector coupling and the electromagnetic form factors of the D and D* mesons in 2+1 flavor Lattice QCD, we compute the D*D\pi, DD\rho and D*D*\rho coupling constants, which play an important role in describing the charm hadron interactions in terms of meson-exchange models. We also extract the charge radii of D and D* mesons and determine the contributions of the light and charm quarks separately., Comment: 19 pages, 3 figures; added references and comments, published version

The electromagnetic form factors of the spin-3/2 Ω baryons, namely the Ω, Ω∗c , Ω∗ cc and Ωccc, are calculated in full QCD on 323 x 64 PACS-CS lattices with a pION mass of 156(9) MeV. The electric charge radii and magnetic moments from the E0 and M1 multipole form factors are extracted. Results for the electric quadrupole form factor, E2, are also provided. Quark sector contributions are computed individually for each observable and then combined to obtain the baryon properties. Charm quark contributions are observed to be systematically smaller compared to the strange quark contributions in case of the charge radii and magnetic moments. E2 moments of the Ω∗ cc and Ωccc are estimated significantly enough to show that their electric charge distributions are deformed. Properties of the spin-1/2 counterparts of the Ω∗ cc and Ω∗ cc baryons are also computed and a comparison is presented.

In color SU(2) lattice QCD, we investigate colored-diquark distributions in two-hadron scatterings by means of Bethe-Salpeter amplitudes on the lattice. With colored-diquark operators in the Coulomb gauge, we measure components of two colored diquarks realized as intermediate states via one gluon exchange (OGE) processes in hadron scattering. From the colored-diquark distributions, we estimate the dominant range of gluon (color) exchanges between closely located two hadrons. We find that the colored-diquark components are enhanced at the short range ($\leq$0.2 fm) and their tails show the single-exponential damping. In order to distinguish the genuine colored-diquark components originating in the color exchange processes from trivial colored two-quark components contained in two color-singlet hadrons as a result of simple transformation of hadronic basis, we repeat the analyses on the artificially constructed gauge fields, where low- and high-momentum gluon components are decoupled and only restricted pair of quarks can share and exchange low-momentum gluons. We observe qualitatively the same behaviors and confirm that the short-range enhancement of the colored-diquark distributions is the genuine OGE-origin color excitation in hadron scattering., 10 pages, 13 figures

Understanding the thermalization process in a pure quantum system is a challenge in theoretical physics. In this work, we explore possible thermalization mechanism in Yang-Mills(YM) theory by using a positive semi-definite quantum distribution function called a Husimi function which is given by a coarse graining of the Wigner function within the minimum uncertainty. Then entropy is defined in terms of the Husimi function, which is called the Husimi-Wehrl(HW) entropy. We propose two numerical methods to calculate the HW entropy. We find that it is feasible to apply the semi-classical approximation with the use of classical YM equation. It should be noted that the semi-classical approximation is valid in the systems of physical interest including the early stage of heavy-ion collisions. Using a product ansatz for the Husimi function, which is confirmed to reproduce the HW entropy within 20% error (overestimate) for a few-body quantum system, we succeed in a numerical evaluation of HW entropy of YM fields and show that it surely has a finite value and increases in time., The 33rd International Symposium on Lattice Field Theory, 14 -18 July 2015, Kobe International Conference Center, Kobe, Japan - Nonzero Temperature and Density (talks).

We discuss thermalization of isolated quantum systems by using the Husimi-Wehrl entropy evaluated in the semiclassical treatment. The Husimi-Wehrl entropy is the Wehrl entropy obtained by using the Husimi function for the phase space distribution. The time evolution of the Husimi function is given by smearing the Wigner function, whose time evolution is obtained in the semiclassical approximation. We show the efficiency and usefullness of this semiclassical treatment in describing entropy production of a couple of quantum mechanical systems, whose classical counter systems are known to be chaotic. We propose two methods to evaluate the time evolution of the Husimi-Wehrl entropy, the test-particle method and the two-step Monte-Carlo method. We demonstrate the characteristics of the two methods by numerical calculations, and show that the simultaneous application of the two methods ensures the reliability of the results of the Husimi-Wehrl entropy at a given time., 11 pages, 8 figures

We show the lattice QCD results on the axial charge gN*N*A of negative parity nucleon resonances, N* (1535) and N* (1650), which are key clues to the chiral structure in baryon sector. The measurements are performed with up and down dynamical quarks employing the renormalization-group improved gauge action at ? = 1.95 and the O(a) improved clover quark action with the hopping parameters, ? = 0.1375, 0.1390 and 0.1400. In order to properly separate signals of N* (1535) and N* (1650), we construct 2?2 correlation matrices and diagonalize them. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N* (1535) takes small values as gN*N*A ~O(0.1), whereas that of N* (1650) is about 0.5, which is found independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.

We show the first lattice QCD result of the axial charge [Formula: see text] of N* (1535). We perform the measurements with two flavors of dynamical quarks employing the renormalization-group improved gauge action at β = 1.95 and the mean-field improved clover quark action with the hopping parameters, κ = 0.1375, 0.1390 and 0.1400. In order to avoid signal contaminations by N*(1650), we construct 2 × 2 correlation matrices and diagonalize them so that clear signal separation can be found. The wraparound contributions in the correlator, which can be another source of signal contamination, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N*(1535) takes a small value, as [Formula: see text], which is almost independent of quark masses.

We study the narrow decay width of low-lying penta-quark baryons in the QCD string theoryin terms of gluonic excitations. In the QCD string theory, the penta-quark baryon decays via a gluonic-excited state of a baryon and meson system, where a pair of Y-shaped junction and anti-junction is created. Since lattice QCD shows that the lowest gluonic-excitation energy takes a large value of about 1 GeV, the decay of the penta-quark baryon near the threshold is considered as a quantum tunneling process via a highly-excited state (a gluonic-excited state) in the QCD string theory. This mechanism strongly suppresses the decay and leads to an extremely narrow decay width of the penta-quark system., Talk given at International Conference on the Structure of Baryons (Baryons 04) October 25 - 29, 2004, Ecole Polytechnique, Palaiseau, France

In SU(3) lattice QCD, we perform the detailed study for the ground-state three-quark (3Q) potential $V_{\rm 3Q}^{\rm g.s.}$ and the 1st excited-state 3Q potential $V_{\rm 3Q}^{\rm e.s.}$, i.e., the energies of the ground state and the 1st excited state of the gluon field in the presence of the static three quarks. From the accurate calculation for more than 300 different patterns of 3Q systems, the static ground-state 3Q potential $V_{\rm 3Q}^{\rm g.s.}$ is found to be well described by the Coulomb plus Y-type linear potential (Y-Ansatz) within 1%-level deviation. As a clear evidence for Y-Ansatz, Y-type flux-tube formation is actually observed on the lattice in maximally-Abelian projected QCD. For about 100 patterns of 3Q systems, we calculate the 1st excited-state 3Q potential $V_{\rm 3Q}^{\rm e.s.}$, and find a large gluonic-excitation energy $\Delta E_{\rm 3Q} \equiv V_{\rm 3Q}^{\rm e.s.}-V_{\rm 3Q}^{\rm g.s.}$ of about 1 GeV, which gives a physical reason of the success of the quark model even without gluonic excitations. We present also the first study for the penta-quark potential $V_{\rm 5Q}$ in lattice QCD, and find that $V_{\rm 5Q}$ is well described by the sum of the OGE Coulomb plus multi-Y type linear potential., Comment: Invited talk at International Workshop on QCD Down Under, Adelaide, Australia, 10-19 Mar 2004

We study the three-quark and multi-quark potentials in SU(3) lattice QCD. From the accurate calculation for more than 300 different patterns of 3Q systems, the static ground-state 3Q potential $V_{\rm 3Q}^{\rm g.s.}$ is found to be well described by the Coulomb plus Y-type linear potential (Y-Ansatz) within 1%-level deviation. As a clear evidence for Y-Ansatz, Y-type flux-tube formation is actually observed on the lattice in maximally-Abelian projected QCD. For about 100 patterns of 3Q systems, we perform the accurate calculation for the 1st excited-state 3Q potential $V_{\rm 3Q}^{\rm e.s.}$ by diagonalizing the QCD Hamiltonian in the presence of three quarks, and find a large gluonic-excitation energy $\Delta E_{\rm 3Q} \equiv V_{\rm 3Q}^{\rm e.s.}-V_{\rm 3Q}^{\rm g.s.}$ of about 1 GeV, which gives a physical reason of the success of the quark model. $\Delta E_{\rm 3Q}$ is found to be reproduced by the ``inverse Mercedes Ansatz'', which indicates a complicated bulk excitation for the gluonic-excitation mode. We study also the tetra-quark and the penta-quark potentials in lattice QCD, and find that they are well described by the OGE Coulomb plus multi-Y type linear potential, which supports the flux-tube picture even for the multi-quarks. Finally, the narrow decay width of penta-quark baryons is discussed in terms of the QCD string theory., Comment: Invited talk at Int. Conference on Quark Confinement and the Hadron Spectrum 6, Sardinia, Italy, 21-25 Sep 2004

We compute the electromagnetic structures of D and D* mesons, the singly charmed Sigma(c) Omega(c), and the doubly charmed Xi(cc), Omega(cc) baryons in 2+1 flavor Lattice QCD. We extract the charge radii and the magnetic moments of these hadrons. In general, charmed hadrons are found to be more compact as compared to light hadrons. The magnetic moments of the singly charmed baryons are found to be dominantly determined by the light quark and the role of the charm quark is significantly enhanced when it is doubly represented.

We study the thermalization process in classical Yang-Mills (CYM) field theory starting from noisy glasma-like initial conditions by investigating the initial-value sensitivity of trajectories. Kunihiro et al. linked entropy generation to the Kolmogorov-Sinai entropy, which gives the entropy production rate in classical chaotic systems, calculated numerically for CYM fields starting from purely random initial field configurations. In contrast, we here study glasma-like initial conditions. For small random fluctuations we obtain qualitatively similar results while no entropy increase is observed when such fluctuations are absent. We analyze the intermediate time Lyapunov spectrum for several time windows and calculate the Kolmogorov-Sinai entropy. We find a large number of positive Lyapunov exponents at the early stages of time evolution. Also for later times their number is a sizeable fraction of the total number of degrees of freedom. The spectrum of positive Lyapunov exponents at first changes rapidly, but then stabilizes, indicating that the dynamics of the gauge fields approaches a steady state. Thus we conclude that also for glasma-like initial conditions a significant amount of entropy is produced by classical gluon field dynamics., Comment: 12 pages, 9 figures

We evaluate interhadron interactions in quenched two‐color lattice QCD from Bethe‐Salpeter amplitudes, concentrating on S‐wave scattering states of two scalar diquarks (uCγ5d). Between two identical scalar diquarks, we observe repulsion in short‐range region. We define and evaluate the “quark‐exchange part” in the interaction, which is induced by adding quark‐exchange diagrams, or equivalently, by introducing Pauli blocking among some of quarks. The repulsive force in short‐distance region arises only from the “quark‐exchange part”, and disappears when quark‐exchange diagrams are omitted, which is qualitatively consistent with the constituent‐quark model picture that a color‐magnetic interaction among quarks is the origin of repulsion. We also find a universal long‐range attractive force, which enters in any flavor channels of two scalar diquarks and whose interaction range and strength are quark‐mass independent.

Understanding the underlying mechanisms causing rapid thermalization deduced for high-energy heavy ion collisions is still a challenge. To estimate the thermalization time, entropy growth for classical Yang-Mills theories is studied, based on the determination of Lyapunov exponents. Distinct regimes for short, medium and long sampling times are characterized by different properties of their spectrum of Lyapunov exponents. Clarifying the existence of these regimes and their implications for gauge-field dynamics is one of the results of this article. As a phenomenological application we conclude that for pure gauge theories with random initial conditions thermalization occurs within a few $\mathrm{fm}/c$, an estimate which can be reduced by the inclusion of fermions, specific initial conditions, etc.

We evaluate the strangeness-conserving $N N$, $\Sigma\Sigma$, $\Xi\Xi$, $\Lambda\Sigma$ and the strangeness-changing $\Lambda N$, $\Sigma N$, $\Lambda\Xi$, $\Sigma\Xi$ axial charges in lattice QCD with two flavors of dynamical quarks and extend our previous work on pseudoscalar-meson-octet-baryon coupling constants so as to include $\pi\Xi\Xi$, $K\Lambda\Xi$ and $K\Sigma\Xi$ coupling constants. We find that the axial charges have rather weak quark-mass dependence and the breaking in SU(3)-flavor symmetry is small at each quark-mass point we consider., Comment: 6 pages, 6 figures. Added discussions and a figure; version to appear in Physics Letters B

Low-lying $\ensuremath{\Lambda}$ baryons with spin $1/2$ are analyzed in full (unquenched) lattice QCD. We construct $2\ifmmode\times\else\texttimes\fi{}2$ cross correlators from flavor SU(3) octet and singlet baryon operators, and diagonalize them so as to extract information of two low-lying states for each parity. The two-flavor $CP$-PACS gauge configurations are used, which are generated in the renormalization-group improved gauge action and the $\mathcal{O}(a)$-improved quark action. Three different $\ensuremath{\beta}$'s, $\ensuremath{\beta}=1.80$, 1.95, and 2.10, are employed, whose corresponding lattice spacings are $a=0.2150$, 0.1555, and 0.1076 fm. For each cutoff, we use four hopping parameters, (${\ensuremath{\kappa}}_{\mathrm{val}},{\ensuremath{\kappa}}_{\mathrm{sea}}$), which correspond to the pion masses ranging about from 500 MeV to 1.1 GeV. Results indicate that there are two negative-parity $\ensuremath{\Lambda}$ states nearly degenerate at around 1.6 GeV, while no state as low as $\ensuremath{\Lambda}(1405)$ is observed. By decomposing the flavor components of each state, we find that the lowest (1st-excited) negative-parity state is dominated by flavor-singlet (flavor-octet) component. We also discuss meson-baryon components of each state, which has drawn considerable attention in the context of multiquark pictures of $\ensuremath{\Lambda}(1405)$.

We evaluate the pseudoscalar-meson coupling constants and the strangeness-conservingand the strangeness-changing axial charges of octet baryons in lattice QCD with two flavors ofdynamical quarks.We find that the coupling constants and the axial charges have rather weak quarkmassdependence and the breaking in SU(3)-flavor symmetry is small at each quark-mass point weconsider. Yukawa International Program for Quark-Hadron Sciences ; KAKENHI post-print

We evaluate interhadron interactions in two-color lattice QCD from Bethe-Salpeter amplitudes on the Euclidean lattice. The simulations are performed in quenched SU(2) QCD with the plaquette gauge action at $\beta = 2.45$ and the Wilson quark action. We concentrate on S-wave scattering states of two scalar diquarks. Evaluating different flavor combinations with various quark masses, we try to find out the ingredients in hadronic interactions. Between two scalar diquarks ($u C\gamma_5 d$, the lightest baryon in SU(2) system), we observe repulsion in short-range region, even though present quark masses are not very light. We define and evaluate the "quark-exchange part" in the interaction, which is induced by adding quark-exchange diagrams, or equivalently, by introducing Pauli blocking among some of quarks. The repulsive force in short-distance region arises only from the "quark-exchange part", and disappears when quark-exchange diagrams are omitted. We find that the strength of repulsion grows in light quark-mass regime and its quark-mass dependence is similar to or slightly stronger than that of the color-magnetic interaction by one-gluon-exchange (OGE) processes. It is qualitatively consistent with the constituent-quark model picture that a color-magnetic interaction among quarks is the origin of repulsion. We also find a universal long-range attractive force, which enters in any flavor channels of two scalar diquarks and whose interaction range and strength are quark-mass independent. The weak quark-mass dependence of interaction ranges in each component implies that meson-exchange contributions are small and subdominant, and the other contributions, {\it ex.} flavor exchange processes, color-Coulomb or color-magnetic interactions, are considered to be predominant, in the quark-mass range we evaluated., Comment: 14 pages, 20 figures

We show the first lattice QCD results on the axial charges $g_A^{N^*N^*}$ of $N^*(1535)$ and $N^*(1650)$. The measurements are performed with two flavors of dynamical quarks employing the renormalization-group improved gauge action at $\beta$=1.95 and the mean-field improved clover quark action with the hopping parameters, $\kappa$=0.1375, 0.1390 and 0.1400. We construct 2$\times$2 correlation matrices and diagonalize them so that the signals of $N^*(1535)$ and $N^*(1650)$ are properly separated. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. The axial charge of $N^*(1535)$ is found to take small values as $g_A^{N^*N^*}\sim {\mathcal O}(0.1)$, whereas that of $N^*(1650)$ is approximately 0.5, which is almost independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model., Comment: 4 pages, 2 figures, presented at the 14th High-Energy Physics International Conference on Quantum ChromoDynamics (QCD08) Montpellier, France, 7-12 July, 2008

We evaluate the $\pi N!N$, $\pi\Sigma\Sigma$, $\pi\Lambda\Sigma$, $K\Lambda N$ and $K \Sigma N $ coupling constants and the corresponding monopole masses in lattice QCD with two flavors of dynamical quarks. The parameters representing the SU(3)-flavor symmetry are computed at the point where the three quark flavors are degenerate at the physical $s$-quark mass. In particular, we obtain $\alpha\equiv F/(F+D)=0.395(6)$. The quark-mass dependences of the coupling constants are obtained by changing the $u$- and the $d$-quark masses. We find that the SU(3)-flavor parameters have weak quark-mass dependence and thus the SU(3)-flavor symmetry is broken by only a few percent at each quark-mass point we consider., Comment: 6 pages, 7 figures, version to be published in PRD

We show the first lattice QCD results on the axial charge ${g}_{A}^{{N}^{*}{N}^{*}}$ of ${N}^{*}(1535)$ and ${N}^{*}(1650)$. The measurements are performed with two flavors of dynamical quarks employing the renormalization-group improved gauge action at $\ensuremath{\beta}=1.95$ and the mean-field improved clover quark action with the hopping parameters, $\ensuremath{\kappa}=0.1375$, 0.1390, and 0.1400. In order to properly separate signals of ${N}^{*}(1535)$ and ${N}^{*}(1650)$, we construct $2\ifmmode\times\else\texttimes\fi{}2$ correlation matrices and diagonalize them. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of ${N}^{*}(1535)$ takes small values such as ${g}_{A}^{{N}^{*}{N}^{*}}\ensuremath{\sim}\mathcal{O}(0.1)$, whereas that of ${N}^{*}(1650)$ is about 0.5, which is found independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.

We perform the first study for the bound states of colored scalar particles ϕ (“scalar quarks”) in terms of mass generation with quenched SU (3)c lattice QCD. We investigate the bound states of ϕ, ϕ†ϕ and ϕϕϕ (“scalar-quark hadrons”), as well as the bound states of ϕ and quarks ψ, i.e., ϕ†ψ, ψψϕ and ϕϕψ (“chimera hadrons”). All these new-type hadrons including ϕ have a large mass of several GeV due to large quantum corrections by gluons, even for zero bare scalar-quark mass mϕ = 0 at a−1 ~ 1 GeV . We find a similar mψ-dependence between ϕ†ψ and ϕϕψ, which indicates their similar structure due to the large mass of ϕ. From this study, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluons.

In terms of mass generation in the strong interaction without chiral symmetry breaking, we perform the first study for light scalar-quarks $\ensuremath{\phi}$ (colored scalar particles with ${\mathbf{3}}_{c}$ or idealized diquarks) and their color-singlet hadronic states using quenched $\mathrm{SU}(3{)}_{c}$ lattice QCD with $\ensuremath{\beta}=5.70$ (i.e., $a\ensuremath{\simeq}0.18\text{ }\text{ }\mathrm{fm}$) and lattice size ${16}^{3}\ifmmode\times\else\texttimes\fi{}32$. We investigate ``scalar-quark mesons'' ${\ensuremath{\phi}}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{\phi}$ and ``scalar-quark baryons'' $\ensuremath{\phi}\ensuremath{\phi}\ensuremath{\phi}$ as the bound states of scalar-quarks $\ensuremath{\phi}$. We also investigate the color-singlet bound states of scalar-quarks $\ensuremath{\phi}$ and quarks $\ensuremath{\psi}$, i.e., ${\ensuremath{\phi}}^{\ifmmode\dagger\else\textdagger\fi{}}\ensuremath{\psi}$, $\ensuremath{\psi}\ensuremath{\psi}\ensuremath{\phi}$, and $\ensuremath{\phi}\ensuremath{\phi}\ensuremath{\psi}$, which we name ``chimera hadrons.'' All the new-type hadrons including $\ensuremath{\phi}$ are found to have a large mass even for zero bare scalar-quark mass ${m}_{\ensuremath{\phi}}=0$ at ${a}^{\ensuremath{-}1}\ensuremath{\simeq}1\text{ }\text{ }\mathrm{GeV}$. We find a ``constituent scalar-quark/quark picture'' for both scalar-quark hadrons and chimera hadrons. Namely, the mass of the new-type hadron composed of $m$ $\ensuremath{\phi}$'s and $n$ $\ensuremath{\psi}$'s, ${M}_{m\ensuremath{\phi}+n\ensuremath{\psi}}$, approximately satisfies ${M}_{m\ensuremath{\phi}+n\ensuremath{\psi}}\ensuremath{\simeq}m{M}_{\ensuremath{\phi}}+n{M}_{\ensuremath{\psi}}$, where ${M}_{\ensuremath{\phi}}$ and ${M}_{\ensuremath{\psi}}$ are the constituent scalar-quark and quark masses, respectively. We estimate the constituent scalar-quark mass ${M}_{\ensuremath{\phi}}$ for ${m}_{\ensuremath{\phi}}=0$ at ${a}^{\ensuremath{-}1}\ensuremath{\simeq}1\text{ }\text{ }\mathrm{GeV}$ as ${M}_{\ensuremath{\phi}}\ensuremath{\simeq}1.5--1.6\text{ }\text{ }\mathrm{GeV}$, which is much larger than the constituent quark mass ${M}_{\ensuremath{\psi}}\ensuremath{\simeq}400\text{ }\text{ }\mathrm{MeV}$ in the chiral limit. Thus, scalar quarks acquire a large mass due to large quantum corrections by gluons in the systems including scalar quarks. Together with other evidences of mass generation of glueballs and charmonia, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects. In addition, the large mass generation of pointlike colored scalar particles indicates that plausible diquarks used in effective hadron models cannot be described as the pointlike particles and should have a much larger size than $a\ensuremath{\simeq}0.2\text{ }\text{ }\mathrm{fm}$.

Light scalar-quarks \phi (colored scalar particles or idealized diquarks) and their color-singlet hadronic states are studied with quenched SU(3)_c lattice QCD in terms of mass generation. We investigate ``scalar-quark mesons'' \phi^\dagger \phi and ``scalar-quark baryons'' \phi\phi\phi as the bound states of scalar-quarks \phi. We also investigate the bound states of scalar-quarks \phi and quarks \psi, i.e., \phi^\dagger \psi, \psi\psi\phi and \phi\phi\psi, which we name ``chimera hadrons''. All the new-type hadrons including \phi are found to have a large mass due to large quantum corrections by gluons, even for zero bare scalar-quark mass m_\phi=0 at a^{-1}\sim 1{\rm GeV}. We conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects., Comment: Talk given at The 17th International Spin Physics Symposium (SPIN2006), Kyoto, Japan, 2-7 Oct 2006

We study multi-quark (3Q,4Q,5Q) systems in lattice QCD. We perform the detailed studies of multi-quark potentials in lattice QCD to clarify the inter-quark interaction in multi-quark systems. We find that all the multi-quark potentials are well described by the OGE Coulomb plus multi-Y-type linear potential, i.e., the multi-Y Ansatz. For multi-quark systems, we observe lattice QCD evidences of ``flip-flop'', i.e., flux-tube recombination. These lattice QCD studies give an important bridge between elementary particle physics and nuclear physics., A talk given at Particles and Nuclei International Conference(PANIC05), Santa Fe, NM, Oct. 24-28, 2005. 3 pages, 6 figures

We study the meson-meson and meson-baryon interactions in lattice QCD. The simulation is performed on 20^3 * 24 lattice at ��=5.7 using Wilson gauge action and Wilson fermion at the quenched level. By adopting one static quark for each hadron as "heavy-light meson" and "heavy-light-light baryon", we define the distance $r$ of two hadrons and extract the inter-hadron potential from the energy difference of the two-particle state and its asymptotic state. We find that both of the meson-meson and meson-baryon potentials are nontrivially weak for the whole range of 0.2 fm, Talk given at Particles and Nuclei International Conference (PANIC05), Santa Fe, NM, USA, 24-28 Oct. 2005. 3 pages, 2 figures

Electromagnetic form factors of D and D* mesons and Xi(cc), Sigma(c), Omega(c), and Omega(cc) baryons are calculated in 2+1 flavor lattice QCD. As a by product of this calculation electric/magnetic charge radii and magnetic moments are extracted. Compared to the PDG values of the light-sector, i.e. pion and proton, charmed hadron results are systematically smaller.

We perform the first study for the static penta-quark (5Q) potential in lattice QCD with $\beta$=6.0 and $16^3 \times 32$ at the quenched level. Accurate results of the 5Q potential are extracted from the 5Q Wilson loop using the smearing method, which enhances the ground-state component. The tetra-quark potential for the $\rm QQ$-$\rm {\bar Q}{\bar Q}$ system is also studied in lattice QCD. The multi-quark potentials are found to be well described as a sum of the one-gluon-exchange Coulomb term and the multi-Y linear confinement term based on the flux-tube picture., Comment: Talk given at the International Workshop on PENTAQUARK04, SPring-8, Japan, 20-23 July 2004

We study the spin $\frac12$ hadronic state in quenched lattice QCD to search for a possible $S=+1$ pentaquark resonance. Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices at $\beta$=5.7 at the quenched level with the standard plaquette gauge action and Wilson quark action. We adopt two independent operators with I=0 and $J^P=\frac12$ to construct a $2\times 2$ correlation matrix. After the diagonalization of the correlation matrix, we successfully obtain the energies of the ground-state and the 1st excited-state in this channel. The volume dependence of the energies suggests the existence of a possible resonance state slightly above the NK threshold in I=0 and $J^P=\frac12^-$ channel., Comment: Talk given at the International Workshop on PENTAQUARK04, SPring-8, Japan, 20-23 July 2004; 7 pages, 3 figures

We study spin $\frac12$ hadronic states in quenched lattice QCD to search for a possible $S=+1$ pentaquark resonance. Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices at $\beta$=5.7 at the quenched level with the standard plaquette gauge action and the Wilson quark action. We adopt a Dirichlet boundary condition in the time direction for the quark to circumvent the possible contaminations due to the (anti)periodic boundary condition for the quark field, which are peculiar to the pentaquark. By diagonalizing the $2\times 2$ correlation matrices constructed from two independent operators with the quantum numbers $(I,J)=(0,\frac12)$, we successfully obtain the energies of the lowest state and the 2nd-lowest state in this channel. The analysis of the volume dependence of the energies and spectral weight factors indicates that a resonance state is likely to exist slightly above the NK threshold in $(I,J^P)=(0,\frac12^-)$ channel., Comment: 21 pages, 14 figures, 1 table; v2: "N_eff" in Sec.4 was changed to "N_fit" to avoid the confusion in the notation; v3: The discussions in Sec.6 were made clearer. Sec7,8,9B were slightly modified. Some references were added; v4: accepted version

We study the excited-state potential and the gluonic excitation in the static three-quark (3Q) system using SU(3) lattice QCD with $16^3\times 32$ at $\beta$=5.8 and 6.0 at the quenched level. For about 100 different patterns of spatially-fixed 3Q systems, we accurately extract the excited-state potential $V_{\rm 3Q}^{\rm e.s.}$ together with the ground-state potential $V_{\rm 3Q}^{\rm g.s.}$ by diagonalizing the QCD Hamiltonian in the presence of three quarks. The gluonic excitation energy $\Delta E_{\rm 3Q} \equiv V_{\rm 3Q}^{\rm e.s.}-V_{\rm 3Q}^{\rm g.s.}$ is found to be about 1 GeV at the typical hadronic scale. This large gluonic-excitation energy is conjectured to give a physical reason of the success of the quark model for low-lying hadrons even without explicit gluonic modes. We investigate the functional form of $\Delta E_{\rm 3Q}$ in terms of the 3Q location. The lattice data of $\Delta E_{\rm 3Q}$ are relatively well reproduced by the ``inverse Mercedes Ansatz'' with the ``modified Y-type flux-tube length'', which indicates that the gluonic-excitation mode is realized as a complicated bulk excitation of the whole 3Q system., Comment: 13pages, 13figures