Anomalous fluctuations in homogeneous fluid phase of active Brownian particles

Abstract

Giant number fluctuations (GNF) are an anomaly universally observed in active fluids with polar or nematic order. In this paper, we show that GNF arise in the fluid phase of active Brownian particles (ABP), where the polar order is absent. GNF in ABP extends over a large but finite length which characterizes the growing velocity correlations. To suppress unwanted phase separation and allow ones to explore the disordered fluid phase at large activities, we impart the inertia, or the mass, to the ABP. A linearized hydrodynamic theory captures our findings, but only qualitatively. We find numerically a nontrivial scaling relation for the density correlation function, which the linearized theory cannot explain. The results suggest ubiquitousness of the anomalous fluctuations even in the disordered homogeneous fluid phase in the absence of the directional order.

15 pages, 10 figures

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• Singular density correlations in chiral active fluids in three dimensions
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• Anti-aligning Self-propelled Model of Two Species: Emergence of Self-organized Heterogeneous Aligned and Clustered Order
• Crystallization of Chiral Active Brownian Particles at Low Densities
• Effect of the background flow on the motility induced phase separation
• A Novel Mechanism of Ordering in a Coupled Driven System: Vacancy Induced Phase Separation