Scaling behavior of non-equilibrium measures in internally driven elastic assemblies

Abstract: Detecting and quantifying non-equilibrium activity is essential for studying internally driven assemblies, including synthetic active matter and complex living systems such as cells or tissue. We discuss a non-invasive approach of measuring non-equilibrium behavior based on the breaking of detailed balance. We focus on "cycling frequencies" - the average frequency with which the trajectories of pairs of degrees of freedom revolve in phase space, and explain their connection with other non-equilibrium measures, including the area enclosing rate and the entropy production rate. We test our approach on simple toy-models comprised of elastic networks immersed in a viscous fluid with site-dependent internal driving. We prove both numerically and analytically that the cycling frequencies obey a power-law as a function of distance between the tracked degrees of freedom. Importantly, the behavior of the cycling frequencies contains information about the dimensionality of the system and the amplitude of active noise. The mapping we use in our analytical approach thus offers a convenient framework for predicting the behavior of two-point non-equilibrium measures for a given activity distribution in the network.