Analysis of the low-energy $\eta$NN-dynamics within a three-body formalism
The interaction of an $\eta$-meson with two nucleons is studied within a three-body approach. The major features of the $\eta NN$-system in the low-energy region are accounted for by using a s-wave separable ansatz for the two-body $\eta N$- and $NN$-amplitudes. The calculation is confined to the $(J^\pi;T)=(0^-;1)$ and $(1^-;0)$ configurations which are assumed to be the most promising candidates for virtual or resonant $\eta NN$-states. The eigenvalue three-body equation is continued analytically into the nonphysical sheets by contour deformation. The position of the poles of the three-body scattering matrix as a function of the $\eta N$-interaction strength is investigated. The corresponding trajectory, starting on the physical sheet, moves around the $\eta NN$ three-body threshold and continues away from the physical area giving rise to virtual $\eta NN$-states. The search for poles on the nonphysical sheets adjacent directly to the upper rim of the real energy axis gives a negative result. Thus no low-lying s-wave $\eta NN$-resonances were found. The possible influence of virtual poles on the low-energy $\eta NN$-scattering is discussed.