Effects of three-nucleon spin-orbit interaction on isotope shifts of Pb nuclei

We investigate the effects of the 3N interaction, which effectively adds a density-dependent term to the LS channel, on the isotopes shifts of the Pb nuclei. With the strength so as to keep the ls splitting of the single-nucleon orbits, the density dependence in the LS channel tends to shrink the wave functions of the j = l + 1/2 orbits while making the j = l - 1/2 functions distribute more broadly. Thereby the kink in the isotope shifts of the Pb nuclei at N = 126 becomes stronger, owing to the attraction from neutrons occupying 0i(11)/(2) in N > 126. The density dependence in the LS channel enables us to reproduce the data of the isotope shifts by the Hartree-Fock-Bogoliubov calculations in a long chain of neutron numbers, even without degeneracy between the n1g(9/2) and n0i(11/2) levels. We exemplify it by the semirealistic M3Y-P6 interaction.