Stochastic Variational Method Applied to Pentaquarks

We perform a five-body calculation for pentaquark (q(4)(q) over bar) state of Lambda(1405) as well as the three-body calculations for the ground state baryons and the Lambda(1405), and two-body calculations for mesons. We take two kinds of hamiltonian; One includes non-relativistic kinetic energy and the other has the semi-relativistic form. Both hamiltonians reproduce reasonably well the energies of ground state baryons (N, Lambda, Sigma, Xi and Delta) and mesons (pi, K, rho, K*). Flavor symmetry breaking (m(s) > m(u,d)) is taken into account. The energy calculated for (q(4)(q) over bar) state of Lambda(1405) is lower than the energy for the (q(3)) state, even after eliminating the contribution from the color van der Waals force due to the phenomenological linear confinement potential. The present result suggests that the Lambda(1405) is a pentaquark-dominated state if the color-magnetic potential plays a leading role of the quark-quark and quark-antiquark interactions.