Effective temperature of active fluids and sheared granular matter

TL;DR

This paper investigates the concept of effective temperature in active fluids and sheared granular matter, showing that simulation results align with analytical models for single active particles, suggesting a unified non-equilibrium description.

Contribution

It demonstrates that effective temperatures from many-body simulations match analytical expressions for single active particles, proposing a unified framework for active and granular systems.

Findings

Effective temperatures fit analytical single-particle models

Simulation data aligns with visco-elastic fluid predictions

Supports a unified non-equilibrium description

Abstract

The dynamics within active fluids, driven by internal activity of the self-propelled particles, is a subject of intense study in non-equilibrium physics. These systems have been explored using simulations, where the motion of a passive tracer particle is followed. Similar studies have been carried out for passive granular matter that is driven by shearing its boundaries. In both types of systems the non-equilibrium motion have been quantified by defining a set of "effective temperatures", using both the tracer particle kinetic energy and the fluctuation-dissipation relation. We demonstrate that these effective temperatures extracted from the many-body simulations fit analytical expressions that are obtained for a single active particle inside a visco-elastic fluid. This result provides testable predictions and suggests a unified description for the dynamics inside active systems.