2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/28812We 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.4 pages, 4 postscript figures (embedded by psfig)Statistical Mechanicstext