$\Lambda$(1405) as a pentaquark

Recent findings of the strangeness +1 particle gives new light to q$^4{\overline{\rm q}}$ systems. Here we apply this method to investigate the features of the old but not-fully-understood baryon: $\Lambda$(1405). From the quark model view points, $\Lambda$(1405) has been considered as the flavor-singlet q$^3$ state with the orbital excitation. On the other hand, it has been reported that the state can also be understood as N${\overline{\rm K}}$ and $\Sigma \pi$ states [1]. Recent works of hyperuclei also suggest that $\Lambda$(1405) may have a more complicated structure than a simple baryon [2]. It is known that the N${\overline{\rm K}}$ (TJ$^P$)=(0 1/2$^-$) state does not have a repulsion from the color-magnetic interaction, CMI. By introducing the mixing among the q$^4{\overline{\rm q}}$ flavor multiplets, we have found that there are two states where CMI are strongly attractive and may form a resonance below the N${\overline{\rm K}}$ theshold. It is also interesting what kind of states they become when the system is bound in nuclei. In the present talk, we will discuss the features of the q$^4{\overline{\rm q}}$ systems with the strangeness $-$1 (TJ$^P$)=(0 1/2$^-$), and argue that this component may be important and should be mixed to the q$^3$ state.\\ \noindent {}[1] V.K.Magas, {\it et.al.}\ hep-ph/0503043.\\ {}[2] T.Suzuki, {\it et.al.}\ PL{\bf B597}(04)263; Y.Akaishi and T.Yamazaki, PR{\bf C65}(02)044005.