Shape coexistence in neutron-deficient Kr isotopes: Constraints on the single-particle spectrum of self-consistent mean-field models from collective excitations

We discuss results obtained in the study of shape coexistence in the neutron-deficient Kr72-78 isotopes. The method that we used is based on the mixing of axial mean-field configurations after their projection on particle number and angular momentum. The calculations are performed with a Skyrme interaction and a density-dependent pairing interaction. Although our calculation reproduces qualitatively and quantitatively many of the global features of these nuclei, such as coexistence of prolate and oblate shapes, their strong mixing at low angular momentum, and the deformation of collective bands, the ordering of our calculated low-lying levels is at variance with experiment. We analyze the role of the single-particle spectrum of the underlying mean field for the spectrum of collective excitations.