Rototaxis: localization of active motion under rotation

TL;DR

This paper introduces roto-taxis, a new concept extending chemotaxis to rotating environments, analyzing how self-propelled particles localize near rotation centers through theoretical and numerical studies of overdamped and inertial dynamics.

Contribution

It extends the concept of taxis to rotating environments and investigates the dynamics of self-propelled particles under rotation, revealing stable trajectories and complex behaviors.

Findings

Overdamped particles can stabilize on epicyclical trajectories.

Inertial effects lead to complex dynamical behaviors.

Results applicable to microorganisms and granular matter in vortices.

Abstract

The ability to navigate in complex, inhomogeneous environments is fundamental to survival at all length scales, giving rise to the rapid development of various subfields in bio-locomotion such as the well established concept of chemotaxis. In this work, we extend this existing notion of taxis to rotating environments and introduce the idea of roto-taxis to bio-locomotion. In particular, we explore both overdamped and inertial dynamics of a model synthetic self-propelled particle in the presence of constant global rotation, focusing on the particle's ability to localize near a rotation center as a survival strategy. We find that in the overdamped regime, the swimmer is in general able to generate a self restoring active torque that enables it to remain on stable epicyclical-like trajectories. On the other hand, for underdamped motion with inertial effects, the intricate competition between self-propulsion and inertial forces, in conjunction with the rototactic torque leads to complex dynamical behavior with non-trivial phase space of initial conditions which we reveal by numerical simulations. Our results are relevant for a wide range of setups, from vibrated granular matter on turntables to microorganisms or animals swimming near swirls or vortices.