Boson expansion techniques, the Pauli principle, and the quasiparticle random phase approximation phase transition - art. no. 064303

The onset of instabilities, in the standard proton-neutron quasiparticle ra ndom phase approximation (QRPA), is investigated by using different boson m appings and trial states belonging to a representation of coherent states. The model describes pairing and proton-neutron interactions. It is shown th at an exact mapping of the Hamiltonian is needed to describe correctly the QRPA phase transition, i.e., that the algebra of all operators participant in the Hamiltonian should be preserved by the boson mapping. Spurious compo nents of the wave functions, which appear if the Pauli principle is violate d, are isolated by construction [S0556-2813(99)05511-9].