Nonequilibrium quantum fields in the large-Nexpansion

Fred Cooper, Salman Habib, Yuval Kluger, Emil Mottola, Juan Pablo Paz, Paul R. Anderson
1994 Physical Review D, Particles and fields  
An effective action technique for the time evolution of a closed system consisting of one or more mean fields interacting with their quantum fluctuations is presented. By marrying large N expansion methods to the Schwinger-Keldysh closed time path (CTP) formulation of the quantum effective action, causality of the resulting equations of motion is ensured and a systematic, energy conserving and gauge invariant expansion about the quasi-classical mean field(s) in powers of 1/N developed. The
more » ... al method is exposed in two specific examples, O(N) symmetric scalar ł^4 theory and Quantum Electrodynamics (QED) with N fermion fields. The ł^4 case is well suited to the numerical study of the real time dynamics of phase transitions characterized by a scalar order parameter. In QED the technique may be used to study the quantum non-equilibrium effects of pair creation in strong electric fields and the scattering and transport processes in a relativistic e^+e^- plasma. A simple renormalization scheme that makes practical the numerical solution of the equations of motion of these and other field theories is described.
doi:10.1103/physrevd.50.2848 pmid:10017918 fatcat:rmujzcu2qjboxf3r67qcfktcmq