Mesonic and isobar degrees of freedom in the ground state of the nuclear many-body system

A study is made in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and infinite nuclear matter of the effects of mesonic and isobar degrees of freedom and the effect of the eikonal form factor in the meson-nucleon vertex of the nucleon-nucleon interaction. Three main effects are seen: First, the mesonic degrees of freedom are found to play a significant role by introducing additional density dependence, which results in a large improvement of the radius with a small change in the energy for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$. Second, when the isobar and mesonic degrees of freedom are combined, repulsion is obtained in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with a corresponding increase of the radius. These results are relatively insensitive to the replacement of part of the pionic form factors by the $\rho$ meson in the transition potentials to intermediate states with $\Delta$ resonances. Third, the use of the eikonal form factor, instead of phenomenological ones of the dipole type, results in additional attraction. This effect persists when the eikonal form factor is used in a potential that includes mesonic degrees of freedom.