title: Thermodynamics of quantum dissipative many-body systems.
abstract: We consider quantum nonlinear many-body 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 for thermodynamic quantities are derived for the case of many degrees of freedom, with general kinetic and dissipative quadratic forms. The underlying scheme is the pure-quantum self-consistent harmonic approximation (PQSCHA), equivalent to the variational approach by the Feynman-Jensen inequality with a suitable quadratic nonlocal trial action. A low-coupling approximation permits us to get manageable PQSCHA expressions for quantum thermal averages with a classical Boltzmann factor involving an effective potential and an inner Gaussian average that describes the fluctuations originating from the interplay of quanticity and dissipation. The application of the PQSCHA to a quantum phi(4) chain with Drude-like dissipation shows nontrivial effects of dissipation, depending upon its strength and bandwidth.
authors.affiliation: Dipartimento di Fisica dell'Università di Firenze and Istituto Nazionale di Fisica della Materia, Largo E. Fermi 2, I-50125 Firenze, Italy. cuccloi@fi.infn.it
authors.forename: A
authors.initials: A
authors.lastname: Cuccoli
authors.forename: A
authors.initials: A
authors.lastname: Fubini
authors.forename: V
authors.initials: V
authors.lastname: Tognetti
authors.forename: R
authors.initials: R
authors.lastname: Vaia