Abstract
A new boson mapping for the group SU(2) × SU(2) is used to generate a perturbation expansion in a small parameter, valid in the deformed regime of the two-dimensional Moszkowski model, without violating angular-momentum conservation at any stage. The corrections to the rotational and vibrational energies and transition matrix elements are obtained to an accuracy one order beyond the RPA. These results are used as a criterion for testing the validity of two methods employing conventional boson expansions about a symmetry-broken minimum and correcting for the symmetry violation a posteriori. It is shown that both methods—that of Marshalek and Weneser, and that of Bes et al., adapted here to boson expansions—reproduce the results of the criterion.
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