The symmetry algebra of the N-dimensional anisotropic quantum harmonic   oscillator with rational ratios of frequencies and the Nilsson model
  The symmetry algebra of the N-dimensional anisotropic quantum harmonic oscillator with rational ratios of frequencies is constructed by a method of general applicability to quantum superintegrable systems. The special case of the 3-dim oscillator is studied in more detail, because of its relevance in the description of superdeformed nuclei and nuclear and atomic clusters. In this case the symmetry algebra turns out to be a nonlinear extension of the u(3) algebra. A generalized angular momentum operator useful for labeling the degenerate states is constructed, clarifying the connection of the present formalism to the Nilsson model in nuclear physics. 
Dennis Bonatsos, C. Daskaloyannis, P. Kolokotronis, D. Lenis