Light-quark contributions to the magnetic form factor of the ? (1405)

In a recent study of the Λ(1405) the suppression of the strange-quark contribution to the magnetic form factor was interpreted as the discovery of a dominant antikaon-nucleon composition for this low-lying state. We confirm this result by calculating the light u and d quark contributions to the Λ(1405) magnetic form factor in lattice QCD in order to determine the extent to which their contributions support this exotic molecular description. Drawing on the recent graded-symmetry approach for the flavor-singlet components of the Λ(1405), the separation of connected and disconnected contributions is performed in both the flavor-octet and -singlet representations. In both cases, the disconnected-loop contributions are found to be large. The relationship between light-quark contributions to the Λ(1405) magnetic form factor and the connected contributions of the nucleon magnetic form factors is established and compared with lattice calculations of the same quantities, confirming the ¯KN molecular structure of the Λ(1405) in lattice QCD