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Register a new userFive-quark picture of Lambda(1405) in anisotropic lattice QCD
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Noriyoshi Ishii
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Five-quark (5Q) picture of Lambda(1405) is studied using quenched lattice QCD with an exotic 5Q operator of Nbar{K} type. To discreminate mere Nbar{K} and Sigmapi scattering states, Hybrid Boundary Condition (HBC), a flavor-dependent boundary condition, is imposed on the quark fields along spatial direction. 5Q mass m_{5Q}simeq 1.89 GeV is obtained after the chiral extrapolation to the physical quark mass region, which is too heavy to be identified with Lambda(1405). Then, Lambda(1405) seems neither a pure 3Q state nor a pure 5Q state, and therefore we present an interesting possibility that Lambda(1405) is a mixed state of 3Q and 5Q states.
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We review briefly recent studies of the Lambda(1405) spectrum in Lattice QCD. Ordinary three-quark pictures of the Lambda(1405) in quenched Lattice QCD fail to reproduce the mass of the experimental value, which seems to support the penta-quark picture for the Lambda(1405) such as a Kbar-N molecule-like state. It is also noted that the present results suffer from relatively large systematic uncertainties coming from the finite volume effect, the chiral extrapolation and the quenching effect.
A new analysis is performed in QCD sum rule for the lightest negative parity baryon Lambda (1405). Mixings of three-quark and five-quark Fock components are taken into account. Terms containing up to dimension 12 condensates are computed in the operator product expansion. It is found that the sum rule gives much stronger coupling of Lambda* to the five-quark operator so that the five-quark components occupy about 90% of Lambda (1405).
We aim to construct quark hadron physics based on QCD. First, using lattice QCD, we study mass spectra of positive-parity and negative-parity baryons in the octet, the decuplet and the singlet representations of the SU(3) flavor. In particular, we consider the lightest negative-parity baryon, the $Lambda$(1405), which can be an exotic hadron as the $N bar K$ molecular state or the flavor-singlet three-quark state. We investigate the negative-parity flavor-singlet three-quark state in lattice QCD using the quenched approximation, where the dynamical quark-anitiquark pair creation is absent and no mixing occurs between the three-quark and the five-quark states. Our lattice QCD analysis suggests that the flavor-singlet three-quark state is so heavy that the $Lambda$(1405) cannot be identified as the three-quark state, which supports the possibility of the molecular-state picture of the $Lambda$(1405). Second, we study thermal properties of the scalar glueball in an anisotropic lattice QCD, and find about 300 MeV mass reduction near the QCD critical temperature from the pole-mass analysis. Finally, we study the three-quark potential, which is responsible to the baryon properties. The detailed lattice QCD analysis for the 3Q potential indicates the Y-type flux-tube formation linking the three quarks.
Within an extended chiral constituent quark model, three- and five-quark structure of the $S_{01}$ resonance $Lambda(1405)$ is investigated. Helicity amplitudes for the electromagnetic decays ($Lambda(1405) to Lambda(1116)gamma$, $Sigma(1194)gamma$), and transition amplitudes for strong decays ($Lambda(1405)toSigma(1194)pi$, $ K^{-}p$) are drived, as well as the relevant decay widths. The experimental value for the strong decay width, $Gamma_{Lambda(1405)to (Sigma pi)^circ}=50pm 2$ MeV, is well reproduced with about 50% of five-quark admixture in the $Lambda(1405)$. Important effects due to the configuration mixings among $Lambda^{2}_{1}P_{A}$, $Lambda^{2}_{8}P_{M}$ and $Lambda^{4}_{8}P_{M}$ are found. In addition, transitions between the three- and five-quark components in the baryons turn out to be significant in both radiative and strong decays of the $Lambda(1405)$ resonance.
We find a strong evidence for the survival of $J/Psi$ and $eta_c$ as spatially-localized $cbar c$ (quasi-)bound states above the QCD critical temperature $T_c$, by investigating the boundary-condition dependence of their energies and spectral functions. In a finite-volume box, there arises a boundary-condition dependence for spatially spread states, while no such dependence appears for spatially compact states. In lattice QCD, we find almost {it no} spatial boundary-condition dependence for the energy of the $cbar c$ system in $J/Psi$ and $eta_c$ channels for $Tsimeq(1.11-2.07)T_c$. We also investigate the spectral function of charmonia above $T_c$ in lattice QCD using the maximum entropy method (MEM) in terms of the boundary-condition dependence. There is {it no} spatial boundary-condition dependence for the low-lying peaks corresponding to $J/Psi$ and $eta_c$ around 3GeV at $1.62T_c$. These facts indicate the survival of $J/Psi$ and $eta_c$ as compact $cbar c$ (quasi-)bound states for $T_c < T < 2T_c$.
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