Exotic quark structure of Λ(1405) and scalar nonet in QCD sum rule

Mixing of multi-quark components in the non-singlet scalar mesons and the flavor singlet Λ(1405) baryon with negative parity are studied in the QCD sum rule. We propose a formulation to evaluate cross-correlators of qq¯(qqq) and qqq¯q¯(qqqqq¯) operators and to define mixing of different Fock states in the sum rule. It is applied to the non-singlet scalar mesons and Λ(1405) baryon. We find that the multi-quark operators predict lower masses than the qq¯(qqq) operators and that the multi-quark states are dominant in the lowest mass states.