Coupling an elastic string to an active bath: the emergence of inverse damping
arXiv:2505.18665 · doi:10.1103/g1zm-23sq
Abstract
We consider a slow elastic string with Klein-Gordon dynamics coupled to a bath of run-and-tumble particles. We derive and solve the induced Langevin-Klein-Gordon string dynamics with explicit expressions for the streaming term, friction coefficient, and noise variance. These parameters are computed exactly in a weak coupling expansion. The induced friction is a sum of two terms: one entropic, proportional to the noise variance as in the Einstein relation for a thermal equilibrium bath, and a frenetic contribution that can take both signs. The frenetic part wins for higher bath persistence, making the total friction negative, and hence creating a wave instability akin to inverse Landau damping. However, this acceleration decreases and eventually disappears when the propulsion speed of the active particles becomes much higher. Detailed simulations confirm the initial growth driven by this anti-damping.
5 figures
References in corpus (15)
- Active matter
- Fluctuations and response of nonequilibrium states
- An update on nonequilibrium linear response
- How does a flexible chain of active particles swell?
- Unusual swelling of a polymer in a bacterial bath
- Activity induced collapse and re-expansion of rigid polymers
- Response theory: a trajectory-based approach
- A review of active matter reviews
- Universal Form of Stochastic Evolution for Slow Variables in Equilibrium Systems
- Entropy production of run-and-tumble particles
- A geometric condition for robot-swarm cohesion and cluster-flock transition
- Non-Gaussian fluctuations of a probe coupled to a Gaussian field
- Pushing run-and-tumble particles through a rugged channel
- The induced friction on a probe moving in a nonequilibrium medium
- Local detailed balance for active particle models