ar X iv : n uc l - th / 0 60 20 72 v 1 2 7 Fe b 20 06 Study of Pentaquark and Λ ( 1405 )

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 confinement potential, and the simplest form of color-magnetic interaction with Gaussian form factor. Flavor symmetry breaking (m s > m u,d) is taken into account. The energy calculated for (q 4 ¯ q) state of Λ(1405) is lower than the energy for the (q 3) state. The present result suggests that the Λ(1405) is a pentaquark-dominated state if the color-magnetic potential plays a leading role of the quark-quark and quark-antiquark interactions.