B(E2) anomaly and triaxial deformation in the interacting boson model

Abstract

The influences of triaxial dynamics on the anomalous $E2$ transitional behaviors in the interacting boson model (IBM) have been comprehensively examined without symmetry restrictions. Specifically, different triaxial schemes in the IBM have been analyzed using a general procedure for deriving triaxial rotor modes based on two distinct approaches. The results indicate that the $B(E2)$ anomaly feature, characterized by $B_{4/2}=B(E2;4_1^+\rightarrow2_1^+)/B(E2;2_1^+\rightarrow0_1^+)<1.0$, can occur in all triaxial schemes due to strong band-mixing effects. This finding is further tested in describing the available data for $^{172}$Pt,~$^{168,170}$Os and $^{166}$W using the model constructed upon the extended consistent-$Q$ formula, providing a simple theoretical explanation of the depressed $B_{4/2}$ values observed in the experiments.