Fluctuations and response of nonequilibrium states

TL;DR

This paper derives a generalized fluctuation-response relation for nonequilibrium thermal systems, extending the fluctuation-dissipation theorem by incorporating dynamical activity correlations, applicable to a broad class of first-order dynamics.

Contribution

It introduces a unifying framework for fluctuation-response relations in nonequilibrium systems, independent of detailed dynamics, and extends previous approaches.

Findings

Derived a correction to the fluctuation-dissipation theorem for nonequilibrium states

Unified previous fluctuation-response approaches into a single scheme

Applicable to a wide range of first-order driven thermal systems

Abstract

A generalized fluctuation-response relation is found for thermal systems driven out of equilibrium. Its derivation is independent of many details of the dynamics, which is only required to be first-order. The result gives a correction to the equilibrium fluctuation-dissipation theorem, in terms of the correlation between observable and excess in dynamical activity caused by the perturbation. Previous approaches to this problem are recovered and extended in a unifying scheme.