Exotic nuclei viewed as clusters in the crust of neutron stars

In the inner crust of neutron stars there are clusters which have a similar structure with the neutron-rich nuclei. The clusters and the neutron gas in which they are immersed are commonly treated in the independent Wigner-Seitz cells approximation. Low-energy excitations are analyzed in these 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. 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. Investigations considering interaction between the clusters are called for