title: Dynamics of a homogeneous active dumbbell system.
abstract: We analyze the dynamics of a two-dimensional system of interacting active dumbbells. We characterize the mean-square displacement, linear response function, and deviation from the equilibrium fluctuation-dissipation theorem as a function of activity strength, packing fraction, and temperature for parameters such that the system is in its homogeneous phase. While the diffusion constant in the last diffusive regime naturally increases with activity and decreases with packing fraction, we exhibit an intriguing nonmonotonic dependence on the activity of the ratio between the finite-density and the single-particle diffusion constants. At fixed packing fraction, the time-integrated linear response function depends nonmonotonically on activity strength. The effective temperature extracted from the ratio between the integrated linear response and the mean-square displacement in the last diffusive regime is always higher than the ambient temperature, increases with increasing activity, and, for small active force, monotonically increases with density while for sufficiently high activity it first increases and next decreases with the packing fraction. We ascribe this peculiar effect to the existence of finite-size clusters for sufficiently high activity and density at the fixed (low) temperatures at which we worked. The crossover occurs at lower activity or density the lower the external temperature. The finite-density effective temperature is higher (lower) than the single dumbbell one below (above) a crossover value of the Péclet number.
authors.affiliation: SISSA-Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, 34136 Trieste, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Suma
authors.affiliation: Dipartimento di Fisica, Università di Bari and INFN, Sezione di Bari, via Amendola 173, Bari I-70126, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Gonnella
authors.affiliation: Dipartimento di Fisica, Università di Bari and INFN, Sezione di Bari, via Amendola 173, Bari I-70126, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Laghezza
authors.affiliation: Istituto Applicazioni Calcolo, CNR, via Amendola 122/D, Bari I-70126, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Lamura
authors.affiliation: Dipartimento di Fisica, Università di Bari and INFN, Sezione di Bari, via Amendola 173, Bari I-70126, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Mossa
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie, Paris 6, Laboratoire de Physique Théorique et Hautes Energies, 4, Place Jussieu, Tour 13, 5ème étage, 75252 Paris Cedex 05, France.
authors.forename: Leticia F
authors.initials: LF
authors.lastname: Cugliandolo