Two-quasiparticle states in the IBA and asymmetric rotor model and the high-spin anomaly in the Hg isotopes

The spectra of the odd but especially of the even mass 194-199Hg isotopes are calculated by coupling one- und two-fermion quasiparticle states to a case which is either described by an asymmetric Davydov rotor or by the IBA model. The fermion states in the IBA model are renormalized to correct for the lack of orthogonality with the boson basis. Renormalization of a standard nuclear many-body hamiltonian leads in a natural way to fermion number mixing in the effective interaction. In both models we obtain good agreement for the energies, transition probabilities and g-factors. It is essential to admix 2-q.p. isub(13/2) neutron states to understand the anomalies of the yrast states near angular momenta 8+, 10+ and 12+. (orig.)