Probing Nonequilibrium Fluctuations through Linear Response

TL;DR

This paper explores how linear response theory reveals unique fluctuation-response relations in nonequilibrium steady states, highlighting features absent in equilibrium, such as irreversible circulation and asymmetries.

Contribution

It introduces two distinct fluctuation-response relations in nonequilibrium steady states, emphasizing the roles of irreversible circulation and asymmetry in fluctuations.

Findings

Identification of symmetric fluctuation-response relation involving irreversible circulation

Discovery of anti-symmetric relation linking fluctuation and response asymmetries

Characterization of fluctuation features unique to nonequilibrium conditions

Abstract

Linear response analysis in the nonequilibrium steady state (Gaussian regime) provides two independent fluctuation-response relations. One, in the form of the symmetric matrix, manifests the departure from the equilibrium formula through the quantity so-called {\it irreversible circulation}. The other, in the anti-symmetric form, connects the asymmetries in the fluctuation and the response function. These formulas represent characteristic features of fluctuations far from equilibrium, which have no counterparts in thermal equilibrium.