Only the ambidextrous can flock: two-dimensional chiral malthusian flocks, time cholesterics, and the KPZ equation
File(s)
Published version
Author(s)
Chen, Leiming
Lee, Chiu Fan
Toner, John
Type
Journal Article
Abstract
We study the hydrodynamic behavior of two-dimensional chiral dry Malthusian flocks; that is, chiral polar-ordered active matter with neither number nor momentum conservation. We show that, in the absence of fluctuations, such systems generically form a “time cholesteric”, in which the velocity of the entire system rotates uniformly at a fixed frequency b. Fluctuations about this state
belong to the universality class of (2+1)-dimensional Kardar-Parisi-Zhang (KPZ) equation, which implies short-ranged orientational order in the hydrodynamic limit. We then show that, in the limit of weak chirality, the hydrodynamics of a system with reasonable size is expected to governed
by the linear regime of the KPZ equation, exhibiting quasi-long-ranged orientational order. Our predictions for the velocity and number density correlations are testable in both simulations and experiments.
belong to the universality class of (2+1)-dimensional Kardar-Parisi-Zhang (KPZ) equation, which implies short-ranged orientational order in the hydrodynamic limit. We then show that, in the limit of weak chirality, the hydrodynamics of a system with reasonable size is expected to governed
by the linear regime of the KPZ equation, exhibiting quasi-long-ranged orientational order. Our predictions for the velocity and number density correlations are testable in both simulations and experiments.
Date Issued
2026-04-23
Date Acceptance
2026-03-16
Citation
Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, 2026, 113 (1)
ISSN
1539-3755
Publisher
American Physical Society
Journal / Book Title
Physical Review E: Statistical, Nonlinear, and Soft Matter Physics
Volume
113
Issue
1
Copyright Statement
© Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI
License URL
Identifier
10.1103/sj5y-8dsd
Publication Status
Published
Article Number
045419
Date Publish Online
2026-04-23