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In medium eta' mass and eta' N interaction based on chiral effective theory

The in-medium eta' mass and the eta'N interaction are investigated in an effective theory based on the linear realization of the SU(3) chiral symmetry. We find that a large part of the eta' mass is generated by the spontaneous breaking of chiral symmetry through the U_A (1) anomaly. As a consequence of this observation, the eta' mass is reduced in nuclear matter where chiral symmetry is partially restored. In our model, the mass reduction is found to be 80MeV at the saturation density. Estimating the eta' N interaction based on the same effective theory, we find that the eta' N interaction in the scalar channel is attractive sufficiently to form a bound state in the eta' N system with a several MeV binding energy. We discuss the origin of attraction by emphasizing the special role of the sigma meson in the linear sigma model for the mass generation of eta' and N.