Dresden 2026 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 55: Focus Session: Emergent Transport in Active Systems (joint session DY/BP)

DY 55.5: Invited Talk

Thursday, March 12, 2026, 16:45–17:15, ZEU/0160

From non-reciprocal torques towards shape-flexible and res-ponsive prototypic worms — •Holger Stark and Jeanine Shea — Institute of Physics and Astronomy, Theoretical Physics, Techni-sche Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany

Non-reciprocal interactions as seen in active matter allow the formation of novel collective states that are only observable in the non-equilibrium. They may serve as prototypes for mimicking what is observed in the real world or for guiding robotic applications.

We start from non-reciprocal orientational interactions, where an active Brownian particle turns away from its neighbors [1]. By varying range and strength of the torque, we discover novel states such as travelling bands or dynamic flocking. Reversing the sign, makes the orientational interaction cohesive. We combine it with aligning torques and again for varying range and torque strength observe multiple, rotary, and persistent worms as well as an aster state [2]. In particular, the persistent worm represents a prototype for a flock of active constituents, either natural or robotic, which shows a remarkable flexibility and integrity when performing shape changes. This becomes obvious when hunting a prey, which leaders inside the worm sense via some chemotactic mechanism. In contrast to the macroscopic world, here without inertia, moving on a straight line seems the best strategy to escape. We also observe that the worm stays intact, even when squeezing through a narrow, long pore.

[1] M. Knezevic, T. Welker & H. Stark, Sci. Rep. 12, 19437 (2022).

[2] Jeanine Shea & Holger Stark, EPJE 48, 22 (2025).

Keywords: non-reciprocal interactions; flocking; prototypic worms; predator-prey