Time-symmetric fluctuations in nonequilibrium systems

TL;DR

This paper identifies time-reversal symmetric observables in nonequilibrium steady states that satisfy a new fluctuation symmetry, enabling analysis beyond linear response and revealing second-order effects of driving fields.

Contribution

It introduces a novel fluctuation symmetry for time-reversal symmetric observables in nonequilibrium systems, extending fluctuation theorems.

Findings

Identification of observables with symmetry in fluctuations

Derivation of a new reciprocity relation

Revealing second-order effects of driving fields

Abstract

For nonequilibrium steady states, we identify observables whose fluctuations satisfy a general symmetry and for which a new reciprocity relation can be shown. Unlike the situation in recently discussed fluctuation theorems, these observables are time-reversal symmetric. That is essential for exploiting the fluctuation symmetry beyond linear response theory. Besides time-reversal, a crucial role is played by the reversal of the driving fields, that further resolves the space-time action. In particular, the time-symmetric part in the space-time action determines second order effects of the nonequilibrium driving.