Rigged Hilbert spaces and time-asymmetry: the case of the upside-down   simple harmonic oscillator
  The upside-down simple harmonic oscillator system is studied in the contexts of quantum mechanics and classical statistical mechanics. It is shown that in order to study in a simple manner the creation and decay of a physical system by ways of Gamow vectors we must formulate the theory in a time-asymmetric fashion, namely using two different rigged Hilbert spaces to describe states evolving towards the past and the future. The spaces defined in the contexts of quantum and classical statistical mechanics are shown to be directly related by the Wigner function. 
Mario Castagnino, Roberto Diener, Luis Lara and Gabriel Puccini