Non-equilibrium forces following quenches in active and thermal matter

Abstract

Non-equilibrium systems are known to exhibit long-ranged correlations due to conservation of quantities like density or momentum. This, in turn, leads to long-ranged fluctuation-induced (Casimir) forces, predicted to arise in a variety of non-equilibrium settings. Here, we study such forces, which arise transiently between parallel plates or compact inclusions in a gas of particles, following a change ("quench") in temperature or activity of the medium. Analytical calculations, as well as numerical simulations of passive or active Brownian particles, indicate two distinct forces: (i) The immediate effect of the quench is adsorption or desorption of particles of the medium to the immersed objects, which in turn initiates a front of relaxing (mean) density. This leads to time-dependent {\it density-induced forces}. (ii) A long-term effect of the quench is that density fluctuations are modified, manifested as transient (long-ranged) (pair-)correlations that relax diffusively to their (short-ranged) steady-state limit. As a result, transient {\it fluctuation-induced forces} emerge. We discuss the properties of fluctuation-induced and density-induced forces as regards universality, relaxation as a function of time, and scaling with distance between objects. Their distinct signatures allow us to distinguish the two types of forces in simulation data. Finally, we propose several scenarios for their experimental observation.

- Added Journal reference and DOI - Modified title - Fixed minor typos - Added plot of Eq. (32) [16 pages, 11 figures]

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Cited by in corpus (17)

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• Bodies in an Interacting Active Fluid: Far-Field Influence of a Single Body and Interaction Between Two Bodies
• Transient fluctuation-induced forces in driven electrolytes after an electric field quench
• Fluctuation-induced Interactions in Micro- and Nano-systems: Survey of Some Basic Results
• Stochastic dynamics and thermodynamics around a metastable state based on the linear Dean-Kawasaki equation
• Dynamics of the critical Casimir force for a conserved order parameter after a critical quench
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• Correlations and forces in sheared fluids with or without quenching
• Activated diffusiophoresis
• Nonequilibrium mixture dynamics: A model for mobilities and its consequences
• Interplay of quenching temperature and drift in Brownian dynamics
• Algebraic depletion interactions in two-temperature mixtures
• Ballistic propagation of density correlations and excess wall forces in quenched granular media
• The role of dimensionality and geometry in quench-induced nonequilibrium forces