How many dissenters does it take to disorder a flock?

Abstract

We consider the effect of introducing a small number of non-aligning agents\nin a well-formed flock. To this end, we modify a minimal model of active\nBrownian particles with purely repulsive (excluded volume) forces to introduce\nan alignment interaction that will be experienced by all the particles except\nfor a small minority of "dissenters". We find that even a very small fraction\nof dissenters disrupts the flocking state. Strikingly, these motile dissenters\nare much more effective than an equal number of static obstacles in breaking up\nthe flock. For the studied system sizes we obtain clear evidence of scale\ninvariance at the flocking-disorder transition point and the system can be\neffectively described with a finite-size scaling formalism. We develop a\ncontinuum model for the system which reveals that dissenters act like annealed\nnoise on aligners, with a noise strength that grows with the persistence of the\ndissenters' dynamics.\n