Lambda(1405) in a baryon-meson scattering with a bound state embedded in   the continuum
  We investigate Lambda(1405) as a resonance in a coupled channel baryon-meson scattering with a `bound state embedded in the continuum'(BSEC). This BSEC is introduced by hand, as a state not originated from simple baryon-meson systems. We assume it comes from the three-quark state.   There appears a resonance in the Sigma pi scattering below the N Kbar threshold when the N Kbar channel is taken to be strongly attractive. It occurs without introducing a BSEC, just like the chiral unitary approach. When a BSEC is introduced, a resonance also appears with a weaker baryon-meson interaction. The corresponding peak also has a large width, and the N Kbar scattering length is reproduced well. The interaction whose channel dependence is the same as the one originated from the color-magnetic interaction, where no N Kbar attraction exists, also gives a broad peak like Lambda(1405) with help of a BSEC.   It is found that the BSEC coupling which does not vanish at the zero momentum transfer give a larger width. In order to reproduce the observed N Kbar scattering length, introducing a BSEC seems preferable. In our calculation, a model gives an appropriate value when the BSEC contribution to the resonance is roughly half of that of the N Kbar in size. 
Sachiko Takeuchi and Kiyotaka Shimizu