Rotational and translational diffusion in an interacting active dumbbell system

Leticia F. Cugliandolo, Giuseppe Gonnella, and Antonio Suma
Phys. Rev. E 91, 062124 – Published 18 June 2015
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Abstract

We study the dynamical properties of a two-dimensional ensemble of self-propelled dumbbells with only repulsive interactions. This model undergoes a phase transition between a homogeneous and a segregated phase and we focus on the former. We analyze the translational and rotational mean-square displacements in terms of the Péclet number, describing the relative role of active forces and thermal fluctuations, and of particle density. We find that the four distinct regimes of the translational mean-square displacement of the single active dumbbell survive at finite density for parameters that lead to a separation of time scales. We establish the Péclet number and density dependence of the diffusion constant in the last diffusive regime. We prove that the ratio between the diffusion constant and its value for the single dumbbell depends on temperature and active force only through the Péclet number at all densities explored. We also study the rotational mean-square displacement proving the existence of a rich behavior with intermediate regimes only appearing at finite density. The ratio of the rotational late-time diffusion constant and its vanishing density limit depends on the Péclet number and density only. At low Péclet number it is a monotonically decreasing function of density. At high Péclet number it first increases to reach a maximum and then decreases as a function of density. We interpret the latter result advocating the presence of large-scale fluctuations close to the transition, at large-enough density, that favor coherent rotation inhibiting, however, rotational motion for even larger packing fractions.

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  • Received 19 January 2015

DOI:https://doi.org/10.1103/PhysRevE.91.062124

©2015 American Physical Society

Authors & Affiliations

Leticia F. Cugliandolo1,*, Giuseppe Gonnella2,†, and Antonio Suma3,‡

  • 1Sorbonne Universités, Université Pierre et Marie Curie, Paris VI, Laboratoire de Physique Théorique et Hautes Énergies, 4 Place Jussieu, 75252 Paris Cedex 05, France
  • 2Dipartimento di Fisica, Università di Bari and INFN, Sezione di Bari, via Amendola 173, Bari, I-70126, Italy
  • 3SISSA–Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, 34136 Trieste Italy

  • *leticia@lpthe.jussieu.fr
  • gonnella@ba.infn.it
  • antonio.suma@gmail.com

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Issue

Vol. 91, Iss. 6 — June 2015

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