Induced friction on a probe moving in a nonequilibrium medium

Area of Science:

• Statistical Mechanics
• Soft Matter Physics
• Nonlinear Dynamics

Background:

• Understanding probe dynamics in complex media is crucial for various fields.
• Equilibrium systems follow Einstein relations, but nonequilibrium systems present unique challenges.
• Active matter and driven systems exhibit behaviors not seen in equilibrium.

Purpose of the Study:

• To derive the fluctuation dynamics of a slow inertial probe in a nonequilibrium medium.
• To analyze the contributions of entropic and frenetic terms to probe friction.
• To investigate probe behavior in a rotating run-and-tumble medium, including negative friction phenomena.

Main Methods:

• Utilized a combination of the projection-operator method and path-space response theory.
• Assumed time-scale separation between the probe and medium dynamics.
• Derived exact expressions for friction coefficient and noise amplitude in a specific model.

Main Results:

• Friction on the probe is decomposed into an entropic term and a novel frenetic term.
• The frenetic term can be positive or negative, leading to potential probe acceleration.
• Observed a transition to absolute negative friction in a rotating run-and-tumble medium, causing probe runaway and a two-peak stationary momentum distribution.

Conclusions:

• Nonequilibrium media can induce novel dynamics, including self-acceleration of probes.
• The frenetic term is key to understanding friction and acceleration in active or driven systems.
• The findings offer insights into particle transport and dynamics in complex, driven environments.