An agitated oscillator chain

TL;DR

This paper investigates how coupling an oscillator chain to active run-and-tumble particles alters its dynamics, leading to instabilities, nonlinear effects, and self-sustained oscillations.

Contribution

It derives explicit Langevin dynamics for the chain under active bath coupling and reveals nonlinear stabilization mechanisms causing pulsations and spatial oscillations.

Findings

High persistence of active particles induces negative friction and instability.

Nonlinear effects arrest anti-damping, leading to Rayleigh-like oscillations.

Coupling to active matter causes pulsations, spatial oscillations, and velocity persistence.

Abstract

We study how the stationary dynamics of an oscillator chain is modified when coupled to a bath of run-and-tumble particles. First, assuming time-scale separation, we derive the induced Langevin chain dynamics with explicit expressions for the streaming term, friction coefficient, and noise amplitude. At high persistence of the run-and-tumble particle bath, the linear friction turns negative, creating an instability. Second, we find that this anti-damping is arrested at long times due to nonlinear effects, reminiscent of a Rayleigh oscillator. We conclude that a passive harmonic chain can be transformed by its coupling to active matter into a self-sustained fluctuating medium with many-body Rayleigh-like dynamics. That transfer of activity results in pulsations of the displacements, spatial oscillations, and the emergence of persistence in velocities along the chain.