Eta-meson light nucleus scattering and Charge Symmetry Breaking
The \eta-meson collision with light nuclei, ^2H, ^3H, ^3He, and ^4He, is considered on the basis of a microscopic approach which utilises Faddeev type and Lippmann-Schwinger equations. The nuclear hamiltonian is approximated by the finite rank approximation which amounts to the coherent approximation. The \eta-nucleus scattering length and the resonance and bound--state poles of the amplitude describing elastic scattering of \eta-meson by these nuclei are obtained. For each of the nuclei considered, the minimal factor enhancing the \eta N--attraction that moves the poles to the quasi--bound state area of the complex k--plane, is determined. It is shown that within the existing uncertainties in the elementary \eta N iteraction all these nuclei can support a quasi--bound state which can result in a formation of an eta-mesic nucleus. Various aspects of the eta-nucleus physics are discussed with specific emphasis given to the \eta--nucleus effective interaction in configuration space (constructed via the Marchenko inverse scattering method), to the Okubo--Zweig--Iizuka (OZI) rule, and to the charge symmetry breaking problem.