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

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.

5 pges, 2 figures. This new version has essentially the same content as the earlier one, but differs cosmetically, and is the version actually submitted to PRL. The accompanying long paper is titled "A novel nonequilibrium state of matter: a $d=4-\epsilon$ expansion study of Malthusian flocks"

References in corpus (5)

• Novel type of phase transition in a system of self-driven particles
• Collective motion of self-propelled particles interacting without cohesion
• Nonmutual torques and the unimportance of motility for long-range order in two-dimensional flocks
• Quantitative Assessment of the Toner and Tu Theory of Polar Flocks
• A novel nonequilibrium state of matter: a $d=4-\epsilon$ expansion study of Malthusian flocks

Cited by in corpus (14)

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• Lift force in odd compressible fluids
• Metastability of Constant-Density Flocks
• Scaling Law and Universal Drop Size Distribution of Coarsening in Conversion-Limited Phase Separation
• A novel nonequilibrium state of matter: a $d=4-\epsilon$ expansion study of Malthusian flocks
• Packed swarms on dirt: two-dimensional incompressible flocks with quenched and annealed disorder
• Evidence of fluctuation-induced first-order phase transition in active matter
• A new universality class describes Vicsek's flocking phase in physical dimensions
• Novel critical phenomena in compressible polar active fluids: Dynamical and Functional Renormalization Group Studies
• Don't look back: Ordering and defect cloaking in non-reciprocal lattice XY models
• Thermodynamic constraints and exact scaling exponents of flocking matter
• Active Jamming at Criticality
• An Infinite Set of Integral Formulae for Polar, Nematic, and Higher Order Structures at the Interface of Motility-Induced Phase Separation
• Dynamics of packed swarms: time-displaced correlators of two dimensional incompressible flocks