The eta-meson light nucleus resonances and quasi-bound states
  The position and movement of poles of the amplitude for elastic eta-meson scattering off the light nuclei d, t, ^3He, and ^4He are studied. It is found that, within the existing uncertainties for the elementary eta-N interaction, all these nuclei can support a quasi-bound state. The values of the eta-nucleus scattering lengths corresponding to the critical eta-N interaction which produces a quasi--bound state are given. 
S. A. Rakityansky, S. A. Sofianos, M. Braun, V. B. Belyaev, and W.   Sandhas