Two-quasiparticle states in the interacting boson model. II. Electromagnetic properties in the SU(3) limit

The interacting boson approximation model, extended by allowing one boson to break and form a quasiparticle pair, is investigated in the SU(3) limit. Electromagnetic properties of yrast states are studied for the algebraic analogs of both the decoupling and strong-coupling limits. The effects of a pair-breaking interaction that mixes states with different numbers of quasiparticles are investigated for E2 transitions between yrast states. For the algebraic analog of the decoupling limit, it is shown that the mixing interaction has a strong influence on transitions in the region of crossing between the ground-state band and the lowest two-quasiparticle (2qp) band. The mixing interaction does not change the electromagnetic properties of the states of the ground-state band. This effect is due to the approximate cancellation between self-energy and vertex corrections, which corresponds to the nuclear Ward identity. For the algebraic analog of the strong-coupling limit, the K forbiddeness of E2 transitions between the ground-state band and the lowest 2qp band is high, and therefore the influence of the mixing interaction is negligible.