COLLECTIVE EXCITATIONS: FROM EXOTIC NUCLEI TO THE CRUST OF NEUTRON STARS

Low-energy quadrupole excitations are analyzed in nuclear Fermi systems. The crust of neutron stars provides a unique framework for studying the evolution of low-lying modes from neutron-rich nuclei to a pure neutron gas. We modelize the crust with Wigner-Seitz cells and focus our attention on the Zr and Sn cells with baryon densities equal to 0.02 fm^-3 and 0.04 fm^-3, respectively. It is shown that the excitations with low multipolarities are concentrated almost entirely in one strongly collective mode which exhausts a very large fraction of the energy-weighted sum rule. Since these collective modes are located at very low energies compared to the giant resonances in standard nuclei, they may affect significantly the specific heat of baryonic inner crust matter of neutron stars.