Berlin 2024 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 43: Active Matter IV (joint session DY/BP/CPP)
DY 43.4: Talk
Thursday, March 21, 2024, 10:30–10:45, BH-N 334
Strong Casimir-like Forces in Flocking Active Matter — •Giuseppe Fava1,2, Andrea Gambassi3, and Francesco Ginelli1,2 — 1Dipartimento di Scienza e Alta Tecnologia and Center for Nonlinear and Complex Systems, Università degli Studi dell'Insubria, Como, Italy — 2INFN sezione di Milano, Milano, Italy — 3SISSA International School for Advanced Studies and INFN, via Bonomea 265, 34136 Trieste, Italy
Confining in space the equilibrium fluctuations of statistical systems with long-range correlations is known to result into effective forces on the boundaries.
In this work we demonstrate the occurrence of Casimir-like forces in the non-equilibrium context provided by flocking active matter. In particular, we consider a system of aligning self-propelled particles in two spatial dimensions, which are transversally confined by reflecting or partially reflecting walls. We show that in the ordered flocking phase this confined active vectorial fluid is characterized by extensive boundary layers, as opposed to the finite ones usually observed in confined scalar active matter. A finite-size, fluctuation-induced contribution to the pressure on the wall emerges, which decays slowly and algebraically upon increasing the distance between the walls.
We explain our findings which display a certain degree of universality within a hydrodynamic description of the density and velocity fields.
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Ref: "Strong Casimir-like Forces in Flocking Active Matter", arXiv:2211.02644
Keywords: Casimir; Flocking; Collective motion; Boundaries