Inequivalent Quantization in the Skyrme Model
  Quantum mechanics on manifolds is not unique and in general infinite number of inequivalent quantizations can be considered. They are specified by the induced spin and the induced gauge structures on the manifold. The configuration space of collective mode in the Skyrme model can be identified with $S^{3}$ and thus the quantization is not unique. This leads to the different predictions for the physical observables. 
H. Ikemori, S. Kitakado, H. Nakatani, H. Otsu, T. Sato