Fluctuation relations for anomalous dynamics generated by time-fractional Fokker-Planck equations

TL;DR

This paper investigates how anomalous diffusion described by time-fractional Fokker-Planck equations affects fluctuation relations, revealing deviations from classical relations and identifying conditions under which they hold or break down.

Contribution

The study introduces three variants of time-fractional Fokker-Planck equations, analytically derives their probability distributions, and examines how they modify fluctuation relations compared to classical cases.

Findings

Type C obeys the conventional fluctuation relation.

Types A and B show deviations with time-dependent coefficients.

Analytical PDFs reveal strongly non-Gaussian behaviors.

Abstract

Anomalous dynamics characterized by non-Gaussian probability distributions (PDFs) and/or temporal long-range correlations can cause subtle modifications of conventional fluctuation relations. As prototypes we study three variants of a generic time-fractional Fokker-Planck equation with constant force. Type A generates superdiffusion, type B subdiffusion and type C both super- and subdiffusion depending on parameter variation. Furthermore type C obeys a fluctuation-dissipation relation whereas A and B do not. We calculate analytically the position PDFs for all three cases and explore numerically their strongly non-Gaussian shapes. While for type C we obtain the conventional transient work fluctuation relation, type A and type B both yield deviations by featuring a coefficient that depends on time and by a nonlinear dependence on the work. We discuss possible applications of these types of dynamics and fluctuation relations to experiments.