Entropy generation in cosmological particle creation
  A very simplified model of the Universe is considered in order to propose an alternative approach to the irreversible evolution of the Universe at very early times. The entropy generation at the quantum stage can be thought as a consequence of an instability of the system. Then particle creation arises from this instability. 
Mario A. Castagnino, Fabian H. Gaioli, and Daniel M. Sforza