Effective potential for dissipative quantum systems
  We consider quantum nonlinear systems with dissipation described within the Caldeira-Leggett model, i.e., by a nonlocal action in the path integral for the density matrix. Approximate classical-like formulas are derived in order to evaluate thermal averages of observables: the cases of linear and nonlinear dissipation are considered, and the framework is extended to the case of many degrees of freedom. 
A.Cuccoli, A. Fubini, A.Rossi, V.Tognetti, R.Vaia