Generalized Kadanoff-Baym relation in nonequilibrium quenched models

TL;DR

This paper derives a generalized Kadanoff-Baym relation applicable to nonequilibrium quenched models, unifying equilibrium and post-quench dynamics, and evaluates its validity in exactly solvable cases.

Contribution

It introduces a generalized differential form of the Kadanoff-Baym ansatz valid at all times in quenched models, extending its applicability beyond equilibrium.

Findings

The generalized relation reduces to the fluctuation-dissipation theorem before the quench.

It remains valid after the quench in broad quenched models.

Alternative extensions of the KB ansatz are tested in exactly solvable models.

Abstract

In the context of a broad class of quenched models, we derive a generalized differential form of the Kadanoff-Baym (KB) ansatz which relates the out of equilibrium correlated and spectral Green's functions. This relation holds at any time both before the quench (when it coincides with the fluctuation-dissipation theorem) as well as after it. We also examine, in the context of exactly soluble quenched models, the validity of some of the earlier alternative extensions of the KB ansatz.