Level crossing of particle–hole and mesonic modes in eta-mesonic nuclei

We study eta-meson properties in the infinite nuclear matter and in atomic nuclei with an emphasis on effects of the eta coupling to N∗(1535)-nucleon–hole modes. The N∗(1535) resonance, which dominates the low-energy eta-nucleon scattering, can be seen as a chiral partner of the nucleon. The change of the chiral mass gap between the N∗ and the nucleon in a nuclear medium has an impact on the properties of the eta-nucleus system. If the N∗-nucleon mass gap decreases with a density increase (chiral symmetry restoration) the calculations show the existence of the resonance state at the energy about 60MeV and two bound eta-nucleus states with the binding energies about −80MeV. These states can have strong effect on predicted cross sections of the 12C(γ,p)11B reaction with eta-meson production.