Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions

We have studied the low-lying magnetic spectra of {sup 12}C, {sup 16}O, {sup 40}Ca, {sup 48}Ca, and {sup 208}Pb nuclei within the random phase approximation (RPA) theory, finding that the description of low-lying magnetic states of doubly-closed-shell nuclei imposes severe constraints on the spin and tensor terms of the nucleon-nucleon effective interaction. We first used four phenomenological effective interactions, and we obtained good agreement with the experimental magnetic spectra and, to a lesser extent, with the electron scattering responses. Then we made self-consistent RPA calculations to test the validity of the finite-range Gogny D1 interaction. For all the nuclei under study, we found that this interaction inverts the energies of all the magnetic states forming isospin doublets.