Negative-parity baryon spectra in quenched anisotropic lattice QCD

We investigate the negative-parity baryon spectra in quenched lattice QCD. We employ the anisotropic lattice with standard Wilson gauge and O(a) improved Wilson quark actions at three values of lattice spacings with renormalized anisotropy ξ = aσ/aτ = 4, where aσ and aτ are spatial and temporal lattice spacings, respectively. The negative-parity baryons are measured with the parity projection. In particular, we pay much attention to the lowest SU(3) flavor-singlet negativeparity baryon, which is assigned as the Λ(1405) in the quark model. For the flavor octet and decuplet negative-parity baryons, the calculated masses are close to the experimental values of corresponding lowest-lying negative-parity baryons. In contrast, the flavor-singlet baryon is found to be about 1.7 GeV, which is much heavier than the Λ(1405). Therefore, it is difficult to identify the Λ(1405) to be the flavor-singlet three-quark state, which seems to support an interesting picture of the penta-quark (udsqq̄) state or the NK̄ molecule for the Λ(1405).