Quantum correlation functions and the classical limit
Abstract
We study the transition from the full quantum mechanical description of physical systems to an approximate classical stochastic one. Our main tool is the identification of the closedtimepath (CTP) generating functional of Schwinger and Keldysh with the decoherence functional of the consistent histories approach. Given a degree of coarse graining in which interferences are negligible, we can explicitly write a generating functional for the effective stochastic process in terms of the CTP generating functional. This construction gives particularly simple results for Gaussian processes. The formalism is applied to simple quantum systems, quantum Brownian motion, and quantum fields in curved spacetime. Perturbation theory is also explained. We conclude with a discussion on the problem of the backreaction of quantum fields in spacetime geometry.
 Publication:

Physical Review D
 Pub Date:
 June 2001
 DOI:
 10.1103/PhysRevD.63.125024
 arXiv:
 arXiv:grqc/0011111
 Bibcode:
 2001PhRvD..63l5024A
 Keywords:

 03.65.Yz;
 Decoherence;
 open systems;
 quantum statistical methods;
 General Relativity and Quantum Cosmology;
 Quantum Physics
 EPrint:
 30 pages, latex