Mean field approach of dynamical pattern formation in underdamped active matter with short-ranged alignment and distant anti-alignment interactions

TL;DR

This paper develops a mean field continuum model for underdamped active matter with short-range alignment and long-range anti-alignment interactions, revealing how inertia influences pattern formation and collective motion.

Contribution

It introduces a coarse-grained underdamped model for active matter, extending beyond overdamped approximations, and explores inertia's role in pattern formation and collective dynamics.

Findings

Underdamped dynamics predict structured laning states.

Inertia-induced flows destabilize laning when anti-alignment weakens.

A turbulent regime with strong density fluctuations emerges between ordered states.

Abstract

Many active matter systems, especially on the microscopic scale, are well approximated as overdamped, meaning that any inertial momentum is immediately dissipated by the environment. On the other hand, especially for macroscopic active systems but also for many mesoscopic systems the time scale of inertial motion can become large enough to be relevant for the dynamics. This raises the question how collective dynamics and the resulting states in active matter are influenced by inertia. Therefore, we propose a coarsegrained continuum model for underdamped active matter based on a mean field description for passive systems. Furthermore, we apply the model to a system with interactions that support an alignment on short distances and an antialignment on longer length scales as known in the context of pattern formation due to orientational interactions. Our numerical calculations of the underand overdamped dynamics both predict a structured laning state. However, activity induced convective flows that are only present in the underdamped model destabilize this state when the anti-alignment is weakened, leading to a collective motion state which does not occur in the overdamped limit. A turbulent transition regime between the two states can be characterized by strong density fluctuations and the absence of global ordering.