We investigate the pentaquark system $qqqs\overline{q}$ in a framework of chiral quark model. Two structures, $(qqq)(s\overline{q})$ and $(qqs)(q\overline{q})$, with all possible color, spin, flavor configurations are considered. The calculations show that there several resonance states, $\mathrm{\ensuremath{\Sigma}}\ensuremath{\pi}$ $N\overline{K}$ state $I{J}^{P}=0{\frac{1}{2}}^{\ensuremath{-...

The electromagnetic mean squared radii, 〈r2〉E and 〈r 2〉M, of Λ(1405) are calculated in the chiral unitary model. We describe the excited baryons as dynamically generated resonances in the octet meson and octet baryon scattering. We evaluate values of 〈r2〉E and 〈r 2〉M for the Λ(1405) on the resonance pole and obtain their complex values. We also consider Λ(1405) obtained by neglecting decay chan...

The Kp → ππΣ reaction is studied within a chiral unitary model. The distribution of πΣ states forming the Λ(1405) shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of Γ = 38 MeV. The mechanism for the reaction is largely dominated by the emission of a π prior to the Kp interaction leading to the Λ(1405). This ensures the coupling of the Λ(1405) to th...

0031-9007= The K p ! 0 0 0 reaction is studied within a chiral unitary model. The distribution of 0 0 states forming the 1405 shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of 38 MeV. The mechanism for the reaction is largely dominated by the emission of a 0 prior to the K p interaction leading to the 1405 . This ensures the coupling of the 1405 t...

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 Λ(1405), which can be an exotic hadron as theNK̄ molecular state or the flavor-singlet three-quark s...

The Kp → ππΣ reaction is studied within a chiral unitary model. The distribution of πΣ states forming the Λ(1405) shows, in agreement with a recent experiment, a peak at 1420 MeV and a relatively narrow width of Γ = 38 MeV. This reaction gives maximal possible weight to the second Λ(1405) state found in chiral unitary theories, which is narrow and of higher energy than the nominal Λ(1405). In c...

We review briefly recent studies of the Λ(1405) spectrum in Lattice QCD. Ordinary three-quark pictures of the Λ(1405) in quenched Lattice QCD fail to reproduce the mass of the experimental value, which seems to support the penta-quark picture for the Λ(1405) such as a K̄N molecule-like state. It is also noted that the present results suffer from relatively large systematic uncertainties coming f...

Using QCD sum rule approach we show that the Λ(1405) can be a K̄N molecule-type multiquark state. To do this we assume the Λ(1405) as a K̄N bound state, and choose a K̄N molecular-like interpolating field. It is found that the Λ(1405) is below the K̄N threshold. PACS numbers: 24.85.+p, 14.20.-c, 21.10.Dr Typeset using REVTEX E-mail: [email protected]

We discuss several aspects of the Λ(1405) resonance in relation to the recent theoretical developments in chiral dynamics. We derive an effective single-channel K̄N interaction based on chiral SU(3) coupled-channel approach, emphasizing the important role of the πΣ channel and the structure of the Λ(1405) in K̄N phenomenology. In order to clarify the structure of the resonance, we study the behav...

We perform a five-body calculation for pentaquark (q 4 ¯ q) state of Λ(1405) as well as the three-body calculations for the ground state baryons and the Λ(1405), and two-body calculations for mesons. The hamiltonian, which reproduces reasonably well the energies of ground state baryons (N, Λ, Σ, Ξ and ∆) and mesons (π, K, ρ, K *), includes kinetic energy of semi-relativistic form, linear confin...