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Updated: May 17, 2026

A Micropatterning Assay for Measuring Cell Chirality
Published on: March 11, 2022
Only the ambidextrous can flock: Two-dimensional chiral Malthusian flocks, time cholesterics, and the
Leiming Chen1, Chiu Fan Lee2, John Toner3
1China University of Mining and Technology, School of Materials Science and Physics, Xuzhou Jiangsu 221116, P. R. China.
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 be 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.
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