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Universality class for a nonequilibrium state of matter: A d = 4 − ε expansion study of Malthusian flocks

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Title: Universality class for a nonequilibrium state of matter: A d = 4 − ε expansion study of Malthusian flocks
Authors: Chen, L
Lee, CF
Toner, J
Item Type: Journal Article
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 toa new universality class in spatial dimensionsd >2. We calculate the universal exponents andscaling laws of this new universality class toO( ) in ad= 4− expansion, and find these aredifferent 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 with spatial dimensionsin the range of 2< d≤4. We also obtain a universal amplitude ratio relating the damping oftransverse and longitudinal velocity and density fluctuations in these systems. Furthermore, wefind a universal separatrix in real (r) space between two regions in which the equal time densitycorrelation〈δρ(r,t)δρ(0,t)〉has opposite signs. Our expansion should be quite accurate ind= 3,allowing precise quantitative comparisons between our theory, simulations, and experiments.
Issue Date: 26-Aug-2020
Date of Acceptance: 17-Jul-2020
URI: http://hdl.handle.net/10044/1/81491
DOI: 10.1103/PhysRevE.102.022610
ISSN: 1539-3755
Publisher: American Physical Society
Start Page: 1
End Page: 40
Journal / Book Title: Physical Review E: Statistical, Nonlinear, and Soft Matter Physics
Volume: 102
Issue: 022610
Copyright Statement: ©2020 American Physical Society
Keywords: Science & Technology
Physical Sciences
Physics, Fluids & Plasmas
Physics, Mathematical
Physics
cond-mat.soft
cond-mat.soft
cond-mat.stat-mech
Publication Status: Published
Online Publication Date: 2020-08-26
Appears in Collections:Bioengineering
Faculty of Engineering