Boundary information inflow enhances correlation in flocking

Andrea Cavagna, Irene Giardina, Francesco Ginelli

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The most conspicuous trait of collective animal behavior is the emergence of highly ordered structures. Less obvious to the eye, but perhaps more profound a signature of self-organization, is the presence of long-range spatial correlations. Experimental data on starling flocks in 3D show that the exponent ruling the decay of the velocity correlation function, C(r)~1/r¿, is extremely small, ¿ 1. This result can neither be explained by equilibrium field theory nor by off-equilibrium theories and simulations of active systems. Here, by means of numerical simulations and theoretical calculations, we show that a dynamical field applied to the boundary of a set of Heisenberg spins on a 3D lattice gives rise to a vanishing exponent ¿, as in starling flocks. The effect of the dynamical field is to create an information inflow from border to bulk that triggers long-range spin-wave modes, thus giving rise to an anomalously long-ranged correlation. The biological origin of this phenomenon can be either exogenous - information produced by environmental perturbations is transferred from boundary to bulk of the flock - or endogenous - the flock keeps itself in a constant state of dynamical excitation that is beneficial to correlation and collective response.
Original languageEnglish
Article number168107
Number of pages5
JournalPhysical Review Letters
Volume110
Issue number16
DOIs
Publication statusPublished - 19 Apr 2013

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