Suppression of core polarization in halo nuclei

The effect of core polarization in halo nuclei is studied using a two-frequency shell-model approach: $\hbar\omega_{in}$ for the inner orbits and $\hbar\omega_{out}$ for the outer (halo) orbits. Starting from the Paris and Bonn NN potentials, accurate model-space $G$-matrix is first derived. The core-polarization diagrams $G_{3p1h}$ are then evaluated as a function of $\hbar\omega_{out}$, with $\hbar\omega_{in}$ held fixed. We find that they are largely suppressed for halo nuclei such as $^6\!He$, $^6\!Li$ and $^{11}\!Li$. The calculated {\em di-neutron} $(p_{3/2})^2$ and $(p_{1/2})^2$ and {\em proton-neutron} $(p_{3/2})^2$ energies in these nuclei are also in good agreement with experiments. It is suggested that the fundamental NN interaction can be probed in a clearer and more direct way in halo nuclei than in ordinary nuclei.