Birth, Death, and Horizontal Flight: Malthusian flocks with an easy plane in three dimensions

John Toner

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arXiv · 2407.03071

Birth, Death, and Horizontal Flight: Malthusian flocks with an easy plane in three dimensions

John Toner

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Abstract

I formulate the theory of three dimensional "Malthusian flocks" -- i.e., coherently moving collections of self-propelled entities (such as living creatures) which are being "born" and "dying" during their motion -- whose constituents all have a preference for having their velocity vectors lie parallel to the same two-dimensional plane. I determine the universal scaling exponents characterizing such systems exactly, finding that the dynamical exponent $z=3/2$, the "anisotropy" exponent $\zeta=3/4$, and the "roughness" exponent $\chi=-1/2$. I also give the scaling laws implied by these exponents.

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John Toner. 2024-07-03. Birth, Death, and Horizontal Flight: Malthusian flocks with an easy plane in three dimensions. https://arxiv.org/abs/2407.03071

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