Subtleties in Quantum Mechanical Metastability
  We present a detailed discussion of some features of quantum mechanical metastability. We analyze the nature of decaying (quasistationary) states and the regime of validity of the exponencial law, as well as decays at finite temperature. We resort to very simple systems and elementary techniques to emphasize subtle aspects of the problem. 
R. M. Cavalcanti (PUC-Rio) and C. A. A. de Carvalho (UFRJ)