Universality class for a nonequilibrium state of matter: A
d
=
4
−
ε
expansion study of Malthusian flocks
d
=
4
−
ε
expansion study of Malthusian flocks
File(s)PRE_clean_copy.pdf (989.32 KB)
Accepted version
Author(s)
Chen, Leiming
Lee, Chiu Fan
Toner, John
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.
Date Issued
2020-08-26
Date Acceptance
2020-07-17
Citation
Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, 2020, 102 (022610), pp.1-40
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
Identifier
https://journals.aps.org/pre/abstract/10.1103/PhysRevE.102.022610
Subjects
Science & Technology
Physical Sciences
Physics, Fluids & Plasmas
Physics, Mathematical
Physics
cond-mat.soft
cond-mat.soft
cond-mat.stat-mech
Publication Status
Published
Date Publish Online
2020-08-26