Hydrodynamics of thermal active matter

TL;DR

This paper develops a comprehensive hydrodynamic theory for thermal active matter using Schwinger-Keldysh effective field theory, capturing energy, temperature, and stochastic effects in non-equilibrium systems.

Contribution

It introduces a novel hydrodynamic framework for thermal active matter that incorporates energy balance, temperature variations, and stochastic effects, rooted in symmetry breaking and effective field theory.

Findings

Derived effective field theories for active superfluids and nematics.

Identified the role of fluctuation-dissipation violations in active matter.

Established a basis for understanding activity-induced phase transitions.

Abstract

Active matter concerns many-body systems comprised of living or self-driven agents that collectively exhibit macroscopic phenomena distinct from conventional passive matter. Using Schwinger-Keldysh effective field theory, we develop a novel hydrodynamic framework for thermal active matter that accounts for energy balance, local temperature variations, and the ensuing stochastic effects. By modelling active matter as a driven open system, we show that the source of active contributions to hydrodynamics, violations of fluctuation-dissipation theorems, and detailed balance is rooted in the breaking of time-translation symmetry due to the presence of fuel consumption and an external environmental bath. In addition, our framework allows for non-equilibrium steady states that produce entropy, with a well-defined notion of steady-state temperature. We use our framework of active hydrodynamics to develop effective field theory actions for active superfluids and active nematics that offer a first-principle derivation of various active transport coefficients and feature activity-induced phase transitions. We also show how to incorporate temperature, energy and noise in fluctuating hydrodynamics for active matter. Our work suggests a broader perspective on active matter that can leave an imprint across scales.