QUANTUM-THEORY OF DISSIPATION OF A HARMONIC-OSCILLATOR COUPLED TO A NONEQUILIBRIUM BATH - WIGNER-WEISSKOPF DECAY AND PHYSICAL SPECTRA

We extend the quantum theory of dissipation in the context of a system -reservoir model, where the reservoir in question is kept in a non-equ ilibrium condition. Based on a systematic separation of time scales in volved in the dynamics, appropriate generalizations of the fluctuation -dissipation and Einstein's relations have been pointed our. We show t hat the Wigner-Weisskopf decay of the system mode results in a rate co nstant which, depending on the relaxation of a non-equilibrium bath, i s dynamically modified. We also calculate the time-dependent spectra o f a cavity mode with a suitable gain when the cavity is kept in contac t with a non-equilibrium bath.