Nonadditivity of Fluctuation-Induced Forces in Fluidized Granular Media

TL;DR

This study explores how fluctuation-induced forces between particles in a driven granular fluid can change sign and are nonadditive, revealing complex collective behaviors influenced by system parameters.

Contribution

It demonstrates that fluctuation-induced interactions in granular media are nonpairwise additive and can vary with control parameters, supported by simulation and theoretical analysis.

Findings

Force sign depends on volume fraction, distance, and restitution coefficient.

Interactions are nonpairwise additive with multiple intruders.

Simulation aligns qualitatively with mode coupling theory.

Abstract

We investigate the effective long-range interactions between intruder particles immersed in a randomly driven granular fluid. The effective Casimir-like force between two intruders, induced by the fluctuations of the hydrodynamic fields, can change its sign when varying the control parameters: the volume fraction, the distance between the intruders, and the restitution coefficient. More interestingly, by inserting more intruders, we verify that the fluctuation-induced interaction is not pairwise additive. The simulation results are qualitatively consistent with the theoretical predictions based on mode coupling calculations. These results shed new light on the underlying mechanisms of collective behaviors in fluidized granular media.