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arXiv · 2001.01300

Moving, reproducing, and dying beyond Flatland: Malthusian flocks in dimensions $d>2$

Leiming Chen·Chiu Fan Lee·John Toner
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Abstract

We show that "Malthusian flocks" -- i.e., coherently moving collections of self-propelled entities (such as living creatures) which are being "born" and "dying" during their motion -- belong to a new universality class in spatial dimensions $d>2$. We calculate the universal exponents and scaling laws of this new universality class to $O(\epsilon)$ in an $\epsilon=4-d$ expansion, and find these are different from the "canonical" exponents previously conjectured to hold for "immortal" flocks (i.e., those without birth and death) and shown to hold for incompressible flocks in $d>2$. Our expansion should be quite accurate in $d=3$, allowing precise quantitative comparisons between our theory, simulations, and experiments.

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Leiming Chen, Chiu Fan Lee, John Toner. 2020-01-05. Moving, reproducing, and dying beyond Flatland: Malthusian flocks in dimensions $d>2$. https://doi.org/10.1103/physrevlett.125.098003

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