Breakdown of effective temperature, power law interactions and self-propulsion in a momentum conserving active fluid

TL;DR

This paper investigates how hydrodynamic interactions in momentum conserving active fluids lead to non-Boltzmann behavior, power-law fluctuation interactions, and deviations from effective temperature descriptions in simple colloidal systems.

Contribution

It reveals the breakdown of effective temperature and introduces power-law fluctuation interactions due to hydrodynamics in active fluids, extending understanding of active matter dynamics.

Findings

Hydrodynamic interactions cause non-Boltzmann steady states.

Fluctuation-induced interactions follow a power-law decay.

Active colloids exhibit different dynamics compared to passive colloids in active fluids.

Abstract

Simplest extensions of single particle dynamics in momentum conserving active fluid - that of an active suspension of two colloidal particles or a single particle confined by a wall - exhibit strong departures from Boltzmann behavior, resulting in either a breakdown of an effective temperature description or a steady state with nonzero entropy production rate. This is a consequence of hydrodynamic interactions that introduce multiplicative noise in the stochastic description of the particle positions. This results in fluctuation induced interactions that depend on distance as a power law. We find that the dynamics of activated colloids in a passive fluid, with stochastic forcing localized on the particle, is different from that of passive colloids in an active fluctuating fluid.