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  • Open Access

Spatially structured flocking in a proliferating population of self-propelled organisms without explicit alignment interactions

Seiya Takamura and Nen Saito*

  • Graduate School of Integrated Science for Life, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima City, Hiroshima 739-8526, Japan

  • *Contact author: nensaito@hiroshima-u.ac.jp
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Phys. Rev. Research 7, 033299 – Published 29 September, 2025

DOI: https://doi.org/10.1103/v3gm-vhry

Abstract

While it is well established that self-propelled particles with alignment interactions can exhibit orientational order, the impact of self-replication and annihilation, which are key characteristics in cellular systems, on spatiotemporal order remains poorly understood. To explore the interplay between self-propulsion and self-replication, we introduce the active Brownian bug model, in which self-propelled agents undergo stochastic, density-dependent replication and constant-rate death. Despite the absence of alignment interactions, the system exhibits flocking behavior characterized by high orientational order, while maintaining ordered hexagonal arrays. This emergent order arises from stochastic birth and death processes, offering a mechanism for flocking in proliferating cellular populations.

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Phys. Rev. Research 7, 033299– Published 29 September, 2025
  • Received 31 May 2025
  • Accepted 4 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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