Mode decomposition and unitarity in quantum cosmology, Talk given at the   Second Meeting on Constrained Dynamics and Quantum gravity, Santa Margherita   Ligure, September 17-21, 1996
  Contrary to common belief, there are perspectives for generalizing the notion of positive and negative frequency in minisuperspace quantum cosmology, even when the wave equation does not admit symmetries. We outline a strategy in doing so when the potential is positive. Also, an underlying unitarity structure shows up. Starting in the framework of the Klein-Gordon type quantization, I am led to a result that relies on global features on the model, and that is possibly related to structures encountered in the refined algebraic quantization scheme. 
Franz Embacher