Tensor-force effects on single-particle levels and proton bubble structure around the Z or N=20 magic number

Applying the semirealistic NN interactions that include a realistic tensor force to the Hartree-Fock calculations, we investigate tensor-force effects on the single-particle levels in Ca isotopes. The semirealistic interactions successfully describe the experimental difference between epsilon(p1s(1/2)) and epsilon(p0d(3/2)) (denoted by Delta epsilon(13)) both at Ca-40 and Ca-48, confirming the importance of the tensor force. The tensor force plays a role in the N dependence of Delta epsilon(13) also in neutron-rich Ca nuclei. While the p1s(1/2)-p0d(3/2) inversion is predicted in heavier Ca nuclei as in Ca-48, it takes place only for N >= 46, delayed by the tensor force. We further investigate the possibility of proton bubble structure in Ar, which is suggested by the p1s(1/2)-p0d(3/2) inversion in Ca-48 and more neutron rich Ca nuclei, by using spherical Hartree-Fock-Bogolyubov calculations. Even with the inversion at Ca-48 the pair correlation prohibits prominent bubble distribution in Ar-46. Bubble structure in Ar is unlikely also near the neutron drip line because of either unboundness or deformation. However, Si-34 remains a candidate for proton bubble structure, owing to the large shell gap between p1s(1/2) and p0d(5/2).