In a recent study of the $\mathrm{\Lambda }(1405)$ 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 $\mathrm{\Lambda }(1405)$ 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 $\mathrm{\Lambda }(1405)$, 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 $\mathrm{\Lambda }(1405)$ 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 $\overline{K}N$ molecular structure of the $\mathrm{\Lambda }(1405)$ in lattice QCD.

• Received 22 December 2016

DOI:https://doi.org/10.1103/PhysRevD.95.054510