Evolution of spectral properties along the O(6)-U(5) transition in the   interacting boson model. I. Level dynamics
  We investigate the evolution of quantal spectra and the corresponding wave functions along the [O(6)-U(5)]$\supset$O(5) transition of the interacting boson model. The model is integrable in this regime and its ground state passes through a second-order structural phase transition. We show that the whole spectrum as a function of the Hamiltonian control parameter, as well as structures of all excited states, exhibit rather organized and correlated behaviors, that provide deeper insight into the nature of this transitional path. 
Stefan Heinze, Pavel Cejnar, Jan Jolie, Michal Macek