Speaker: John Toner, PhD, University of Oregon
Title: Only the Ambidextrous Can Flock: 2d Chiral Malthusian Flocks and the KPZ Equation
Abstract: I’ll show that 2d Malthusian flocks (i.e., flocks with birth and death) composed of chiral active agents can not form a long range ordered flocking state (i.e., a state in which the spatially averaged velocity vector <vec{v}> is non-zero,) even though it is well-known that they can order in this way if they are achiral. The argument for this conclusion uses a mapping of this problem onto the 2-space, one-time dimensional KPZ equation. While this conclusion holds in principal for arbitrarily weak chirality, I’ll show that in practice, even for moderately weak chirality, a very large chiral flock (e.g., the size of the observable universe!) can remain well-ordered.