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We study an agent-based model of self-propelled particles with a velocity-dependent alignment rule. This interaction is orientation weighted and acts along the line connecting neighboring particles. Tuning the alignment strength produces…

Soft Condensed Matter · Physics 2026-05-19 Bohdan Dobosh , Alexander Yakimenko

Motivated by recent experimental and computational results that show a motility-induced clustering transition in self-propelled particle systems, we study an individual model and its corresponding Self-Organized Hydrodynamic model for…

Adaptation and Self-Organizing Systems · Physics 2016-02-22 Pierre Degond , Silke Henkes , Hui Yu

We investigate the collective transport properties of microscopic magnetic rollers that propel close to a surface due to a circularly polarized, rotating magnetic field. The applied field exerts a torque to the particles, which induces a…

Soft Condensed Matter · Physics 2022-01-03 Gaspard Junot , Andrejs Cebers , Pietro Tierno

Collective behavior is all around us, from flocks of birds to schools of fish. These systems are immensely complex, which makes it pertinent to study their behavior through minimal models. We introduce such a minimal model for cohesive and…

Soft Condensed Matter · Physics 2025-01-29 Jeanine Shea , Holger Stark

Kinetic and hydrodynamic theories are widely employed for describing the collective behaviour of active matter systems. At the fluctuating level, these have been obtained from explicit coarse-graining procedures in the limit where each…

Statistical Mechanics · Physics 2022-12-14 Ouassim Feliachi , Marc Besse , Cesare Nardini , Julien Barré

Although human beings have known about the phenomenon of "flocking"- that is, the coherent movement of large numbers of creatures (flocks of birds, schools of fish, herds of woolly mammoths, etc.)- since prehistoric times, it is only in the…

Soft Condensed Matter · Physics 2018-12-04 John Toner

Birds in a flock move in a correlated way, resulting in large polarization of velocities. A good understanding of this collective behavior exists for linear motion of the flock. Yet observing actual birds, the center of mass of the group…

We present a hydrodynamic model of flocking that generalizes the familiar Toner-Tu equations to incorporate turning inertia of well-polarized flocks. The continuum equations controlled by only two dimensionless parameters, orientational…

Soft Condensed Matter · Physics 2016-01-20 Xingbo Yang , M. Cristina Marchetti

Within a simple model of attractive active Brownian particles, we predict flocking behavior and challenge the widespread idea that alignment interactions are necessary to observe this collective phenomenon. Here, we show that even…

Soft Condensed Matter · Physics 2023-04-19 Lorenzo Caprini , Hartmut Löwen

We derive the hydrodynamic equations of perfect fluids without boost invariance [1] from kinetic theory. Our approach is to follow the standard derivation of the Vlasov hierarchy based on an a-priori unknown collision functional satisfying…

High Energy Physics - Theory · Physics 2025-10-01 Kevin T. Grosvenor , Niels A. Obers , Subodh P. Patil

We analyse collective motion that occurs during rare (large deviation) events in systems of active particles, both numerically and analytically. We discuss the associated dynamical phase transition to collective motion, which occurs when…

Statistical Mechanics · Physics 2021-02-10 Yann-Edwin Keta , Étienne Fodor , Frédéric van Wijland , Michael E. Cates , Robert L. Jack

Considering a gas of self-propelled particles with binary interactions, we derive the hydrodynamic equations governing the density and velocity fields from the microscopic dynamics, in the framework of the associated Boltzmann equation.…

Statistical Mechanics · Physics 2009-10-09 Eric Bertin , Michel Droz , Guillaume Grégoire

A one-dimensional rule-based model for flocking, that combines velocity alignment and long-range centering interactions, is presented and studied. The induced cohesion in the collective motion of the self-propelled agents leads to a unique…

Statistical Mechanics · Physics 2015-01-19 V. Dossetti

We study in detail the hydrodynamic theories describing the transition to collective motion in polar active matter, exemplified by the Vicsek and active Ising models. Using a simple phenomenological theory, we show the existence of an…

Statistical Mechanics · Physics 2016-01-20 Alexandre P. Solon , Jean-Baptiste Caussin , Denis Bartolo , Hugues Chaté , Julien Tailleur

Collective behavior in biological systems was first captured by the Vicsek model, in which particles align their velocities in the average direction of neighbors, leading to coherent motion and showing an order-disorder transition. However,…

Soft Condensed Matter · Physics 2026-02-26 Mohit Gaur , Arnab Saha , Subhajit Paul

We study theoretically the collective dynamics of particles driven by an optical vortex along a circular path. Phase equations of N particles are derived by taking into account both hydrodynamic and repulsive interactions between them. For…

Adaptation and Self-Organizing Systems · Physics 2019-09-30 Takumi Miyamoto , Masayuki Imai , Nariya Uchida

In this paper, we quantify the asymptotic limit of collective behavior kinetic equations arising in mathematical biology modeled by Vlasov-type equations with nonlocal interaction forces and alignment. More precisely, we investigate the…

Analysis of PDEs · Mathematics 2020-07-10 José A. Carrillo , Young-Pil Choi , Jinwook Jung

Colloidal particles moving in a fluid interact via the induced velocity field. The collective dynamic state for a class of actively forced colloids, driven by harmonic potentials via a rule that couples forces to configurations, to perform…

Soft Condensed Matter · Physics 2011-10-11 Loïc Damet , Giovanni M. Cicuta , Jurij Kotar , Marco Cosentino Lagomarsino , Pietro Cicuta

Collective motion and self-organization of interacting particles, such as flocking and swarming, can be viewed as nonequilibrium analogues of collective dynamics in gases. Motivated by the analogy between gas mixtures and Cucker--Smale…

Analysis of PDEs · Mathematics 2025-11-25 Ziming Bian , Seung-Yeal Ha , Tommaso Ruggeri , Qinghua Xiao

We theoretically describe the dynamics of swimmer populations confined in thin liquid films. We first demonstrate that hydrodynamic interactions between confined swimmers only depend on their shape and are independent of their specific…

Soft Condensed Matter · Physics 2015-06-11 Tommaso Brotto , Jean-Baptiste Caussin , Eric Lauga , Denis Bartolo