Jaksic V., Pillet C.-A.
On a Model for Quantum Friction II.
Fermi's Golden Rule and Dynamics at Positive Temperature.
(276K, postscript)

ABSTRACT.  We investigate the dynamics of an N-level system linearly coupled to a field
of mass-less bosons at positive temperature. Using complex deformation
techniques, we develop time-dependent perturbation theory and study spectral
properties of the total Hamiltonian. We also calculate the lifetime of
resonances to second order in the coupling.