Far-from-equilibrium quantum many-body dynamics

TL;DR

This paper evaluates a real-time quantum many-body dynamics framework using a vertex expansion of the effective action, enabling non-perturbative analysis of strongly interacting systems and late-time nonequilibrium behavior.

Contribution

It introduces a dynamic flow approach based on a closed Keldysh contour, extending previous formalisms to derive time evolution equations beyond 2PI approximations.

Findings

Derivation of time evolution equations for Green functions applicable to strongly interacting systems.

Identification of an s-channel truncation matching 2PI effective action results.

Framework capable of analyzing late-time nonequilibrium quantum dynamics.

Abstract

The theory of real-time quantum many-body dynamics as put forward in Ref. [arXiv:0710.4627] is evaluated in detail. The formulation is based on a generating functional of correlation functions where the Keldysh contour is closed at a given time. Extending the Keldysh contour from this time to a later time leads to a dynamic flow of the generating functional. This flow describes the dynamics of the system and has an explicit causal structure. In the present work it is evaluated within a vertex expansion of the effective action leading to time evolution equations for Green functions. These equations are applicable for strongly interacting systems as well as for studying the late-time behaviour of nonequilibrium time evolution. For the specific case of a bosonic N-component phi^4 theory with contact interactions an s-channel truncation is identified to yield equations identical to those derived from the 2PI effective action in next-to-leading order of a 1/N expansion. The presented approach allows to directly obtain non-perturbative dynamic equations beyond the widely used 2PI approximations.