Microscopic treatment of shape coexistence in even-even nuclei and related extension of IBM

Intruder quasi-rotational bands in tin isotopes are treated on the bases of a microscopic theory developed previously and extended to include proton pp-RPA bosons and hh-RPA bosons in addition to neutron bosons. Nucleons in the core are shown to play a decisive role in the intruder band. It is pointed out that the proton hole and particle bosons and the neutron bosons conspire to deform the nucleus and lower the intruder states to the observed relatively low excitation energies. Some general features of shape coexistence in nuclei are discussed. (orig.)