Regular Article

Effective temperature of active fluids and sheared soft glassy materials

Department of Chemical and Biological Physics, The Weizmann Institute of Science, 76100, Rehovot, Israel

^* e-mail: nir.gov@weizmann.ac.il

Received: 30 March 2018
Accepted: 12 September 2018
Published online: 11 October 2018

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 a soft glassy material 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.