Nuclear halos and drip lines in symmetry-conserving continuum Hartree-Fock-Bogoliubov theory

We review the properties of nuclear halos and nuclear skins in drip line nuclei in the framework of the spherical Hartree-Fock-Bogoliubov (HFB) theory with continuum effects and projection on a good particle number with the Gogny force. We first establish the position of the unprojected HFB drip lines for the two most employed parametrizations of the Gogny force and show that the use of finite-range interactions leads almost always to small-sized halos, even in the least bound nuclei, which is in agreement with most mean-field predictions. We also discuss the size of the neutron skin at the drip line and its relation to neutron asymmetry. The impact of particle-number projection and its conceptual consequences near the drip line are analyzed in detail. In particular, we discuss the role of chemical potential in a projected theory and the criteria required to define the drip line. We show that including particle-number projection can shift the latter, in particular near closed shells. We notice that, as a result, the size of the halo can be increased due to larger pairing correlations. However, combining the most realistic pairing interaction, a proper treatment of the continuum, and particle-number projection does not permit us to reproduce the very large halos observed in very light nuclei.