Vibrations in the O(6) limit of the proton-neutron interacting boson model

A study is made of vibrations in the O(6) limit of the proton-neutron interacting boson model. Using the procedure of Hatch and Levit, the dependence of the classical limit of an O(6) proton-neutron interacting boson model Hamiltonian is deduced, and the associated eigenvalues are found. The states corresponding to single -vibration quanta are pure in the O(6) classification, belonging to the second representations from both the [N,0] and [N-1,1] symmetries. This is in contrast to the U(5) limit, where the antisymmetric vibration corresponds to the lowest mixed-symmetry level.