Dynamical Fluctuation-Response Relations

Abstract

We derive exact dynamical fluctuation-response relations (FRRs) for time-integrated observables of any nonautonomous Markov jump process. The finite-time covariance splits into an initial variability and an integral of response kernels along the driven dynamics. The identity sharpens the dynamical response thermodynamic and kinetic uncertainty relations and fluctuation-response inequalities (FRIs). For autonomous processes, dynamical FRRs yield two complementary frequency-domain relations. Steady-state FRRs are recovered in the long time limit, along with the fluctuation-dissipation theorem and Onsager reciprocity for detailed-balance dynamics. The importance of initial variability for slowly relaxing systems is also highlighted.

Added a physical interpretation of the initial-variability term, illustrated its long-lived regime, and expanded the appendix