Induced interaction stabilizing nuclear matter

Excitation modes of nuclear matter at various densities are investigated including the effects of Δ excitations. Collective features are observed at small densities in the scalar-isoscalar channel and at large densities for the longitudinal isovector mode. Using the Brueckner G-matrix for the residual interaction, the RPA approximation predicts an instability of nuclear matter against these modes. The renormalization of the residual interaction by the so called induced interaction yields a stabilization of the collective modes. The effects of the corresponding phonon exchange terms on the particle-hole interaction and on the effective mass are discussed. 8 refs.; 4 figs