Fore-aft asymmetric flocking

TL;DR

This paper demonstrates that fore-aft asymmetry in flocking models significantly alters phase behavior, leading to coexistence of banded phases and a complex phase diagram, which is likely a generic phenomenon.

Contribution

It reveals how even weak fore-aft asymmetry qualitatively changes flocking phase diagrams, extending understanding beyond symmetric models.

Findings

Asymmetry favors front neighbors, altering phase diagram.

Existence of a 'banded liquid' phase with algebraic density distribution.

Results are supported by hydrodynamic stability analysis.

Abstract

We show that fore-aft asymmetry, a generic feature of living organisms and some active matter systems, can have a strong influence on the collective properties of even the simplest flocking models. Specifically, an arbitrarily weak asymmetry favoring front neighbors changes qualitatively the phase diagram of the Vicsek model. A region where many sharp traveling band solutions coexist is present at low noise strength, below the Toner-Tu liquid, at odds with the phase-separation scenario well describing the usual isotropic model. Inside this region, a `banded liquid' phase with algebraic density distribution coexists with band solutions. Linear stability analysis at the hydrodynamic level suggests that these results are generic and not specific to the Vicsek model.