Linear Response Theory and Fluctuation Dissipation Theorem for Systems with Absorbing States

Prajwal Padmanabha, Sandro Azaele, Amos Maritan

Published 2022-04-06Version 1

The Fluctuation Dissipation Theorem (FDT) is one of the fundamental results of statistical mechanics and is a powerful tool that connects the macroscopic properties to microscopic dynamics. The FDT and the linear response theory are mainly restricted to systems in the vicinity of stationary states. However, frequently, physical systems do not conserve the total probability. In systems with absorbing states, the net flux out of the system is positive, and the total probability decays with time. In this case the stationary distribution is trivially zero throughout and the tools provided by standard linear response theory fail. Here we present a new FDT for decaying systems which connects the response of observables conditioned on survival to conditional correlations without perturbations. The results have been verified through simulations and numerics in various important examples