Fluctuation-Induced Casimir Forces in Granular Fluids

TL;DR

This paper numerically investigates fluctuation-induced Casimir-like forces in driven granular fluids, revealing a long-range repulsive interaction caused by hydrodynamic fluctuations confined between intruders.

Contribution

It introduces a novel mechanism for fluctuation-induced forces in granular media, analogous to the Casimir effect, supported by numerical simulations and theoretical estimates.

Findings

Long-range repulsive force observed between intruders

Force explained by confined hydrodynamic fluctuations

Qualitative agreement between theory and simulations

Abstract

We have numerically investigated the behavior of driven non-cohesive granular media and found that two fixed large intruder particles, immersed in a sea of small particles, experience, in addition to a short range depletion force, a long range repulsive force. The observed long range interaction is fluctuation-induced and we propose a mechanism similar to the Casimir effect that generates it: the hydrodynamic fluctuations are geometrically confined between the intruders, producing an unbalanced renormalized pressure. An estimation based on computing the possible Fourier modes explains the repulsive force and is in qualitative agreement with the simulations.