RELATIVISTIC MEAN-FIELD DESCRIPTION OF COLLECTIVE MOTION IN NUCLEI - THE PION FIELD

The influence of the pion field on isovector dipole and spin-dipole co llective oscillations is investigated in a time-dependent model based on relativistic mean field theory. We find that the inclusion of the l ong range pion-nucleon interaction provides an additional strong dampi ng mechanism for the isovector dipole vibrations. The inclusion of the pion field has also a strong effect on the dynamics of spin-dipole vi brations, and in particular on the splitting of excitation energies of the J(pi) (0(-),1(-),2(-)) components of the isovector spin-dipole re sonance.