Finite temperature amplitudes and reaction rates in Thermofield dynamics
  We propose a method for calculating the reaction rates and transition amplitudes of generic process taking place in a many body system in equilibrium. The relationship of the scattering and decay amplitudes as calculated in Thermo Field Dynamics the conventional techniques is established. It is shown that in many cases the calculations are relatively easy in TFD. 
A. Rakhimov, F.C. Khanna (Univ. of Alberta, Canada)