Eur. Phys. J. E (2018) 41: 49
https://doi.org/10.1140/epje/i2018-11653-4

Regular Article

Active particle condensation by non-reciprocal and time-delayed interactions

¹ Department of Physics, Università degli studi di Trieste, 34127, Trieste, Italy
² The Abdus Salam International Centre for Theoretical Physics, 34151, Trieste, Italy
³ Department of Physics, Savitribai Phule Pune University, 411007, Pune, India

^* e-mail: arnab@physics.unipune.ac.in
^** e-mail: sayeed@physics.unipune.ac.in

Received: 12 October 2017
Accepted: 15 March 2018
Published online: 9 April 2018

Abstract

We consider the flocking of self-propelling agents in two dimensions, each of which communicates with its neighbors within a limited vision-cone. Also, the communication occurs with some time-delay. The communication among the agents are modeled by Vicsek rules. In this study we explore the combined effect of non-reciprocal interaction (induced by limited vision-cone) among the agents and the presence of delay in the interactions on the dynamical pattern formation within the flock. We find that under these two influences, without any position-based attractive interactions or confining boundaries, the agents can spontaneously condense into “drops”. Though the agents are in motion within the drop, the drop as a whole is pinned in space. We find that this novel state of the flock has a well-defined order and it is stabilized by the noise present in the system.