X(3872) and Λ(1405) as multiquark hadrons

The effects of introducing an extra (qq-bar) pair to the X(3872) and Λ(1405) systems are discussed by a quark model. As for the X(3872), we investigate qq-bar cc-bar systems with the orbital correlation. The results show that there can be a bound state of qq-bar cc-bar with JPC=1++, which is a coupled state of the J/ψ-ρ and D-D* molecules with a multiquark configuration in the short range region. The Λ(1405) resonance is treated as a q3-qq-bar scattering which couples to the q3 orbital (0s)20p state by the one-gluon exchange. Due to the coupling of this q3 state, we find that a peak appears at around 1405 MeV. Both of the cases indicate that an extra (qq-bar) pair may play important roles especially in some of the excited hadrons. (author)