Negative-parity baryon spectra in quenched anisotropic lattice QCD

TL;DR

This study uses quenched anisotropic lattice QCD to analyze negative-parity baryon spectra, finding that the Lambda(1405) is unlikely a simple three-quark state, supporting alternative models like penta-quark or molecular structures.

Contribution

First lattice QCD calculation to investigate negative-parity baryons with anisotropic lattices, providing insights into the structure of Lambda(1405).

Findings

Flavor octet and decuplet negative-parity baryons match experimental masses.

The flavor-singlet negative-parity baryon is much heavier than Lambda(1405).

Results suggest Lambda(1405) is not a simple three-quark state.

Abstract

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 xi=a_sigma/a_tau=4, where a_sigma and a_tau 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 negative-parity baryon, which is assigned as the Lambda(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 Lambda(1405). Therefore, it is difficult to identify the Lambda(1405) to be the flavor-singlet three-quark state, which seems to support an interesting picture of the penta-quark (uds qbar q) state or the N-Kbar molecule for the Lambda(1405).