Many-body correlations in shell model effective interactions derived by ab initio methods and the Vlow-k approach

We investigate many-body correlations caused by two-and three-body(2-, 3bd) forces. Shell-model effective interactions derived from ab initio methods(coupled-cluster method, no-core shell model) are adopted.Vlow-k potentials, based on many-body perturbation theory, are also tested, especially for their cut-off dependence.We compare the central, tensor and spin-orbit interactions from microscopic theory to the fitted interactions. After the inclusion of the three-body force, the matrix elements become fairly close to those fitted directly to experimental data. Calculations of neutron-rich oxygen isotopes are performed, to clarify the effects of 3bd forces, tensor, and spin-orbit interactions on the nuclear binding and excitation energies. We find that the 3bd force can influence the binding energies greatly, which also determines the drip line position, while its effect on excitation energies is not very pronounced. The spin-orbit force, which is part of the 2bd force, can affect the shell structure explicitly, at least for neutron-rich systems.