Few-Body Problems with Strangeness

We solve a five-body problem of pentaquark (q4 ) state of Λ(1405). The hamiltonian, which reproduces reasonably well the energies of ground state baryons (N, Λ, Σ, Ξ and Δ) and mesons (π, K, ρ, K*), includes kinetic energy of semi-relativistic form, linear confinement potential, and a color-magnetic interaction with Gaussian form factor. Flavor symmetry breaking (ms> mu,d) is taken into account. The energy calculated for the pentaquark state of Λ(1405) is lower than the energy for the three-quark 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.