Band mixing effects in mean field theories. I. E2 transitions in the interacting boson model 1

The 1/N expansion method, which is an angular momentum projected mean field theory, is used to investigate the nature of electromagnetic transitions in the interacting boson model. Conversely, comparison with the exact interacting boson model results sheds light on the range of validity of the mean field theory. It is shown that the projected mean field results for the E2 transitions among the ground, β, and γ bands are incomplete for the spin-dependent terms, and it is essential to include band mixing effects for a correct (Mikhailov) analysis of E2 data. The algebraic expressions derived are general and will be useful in the analysis of experimental data in terms of both the sd and sdg boson models