Abstract
We study the asymptotic response of polar ordered active fluids ("flocks") to small external aligning fields h. The longitudinal susceptibility χ∥ diverges, in the thermodynamic limit, like h−ν as h→0. In finite systems of linear size L, χ∥ saturates to a value ∼Lγ. The universal exponents ν and γ depend only on the spatial dimensionality d, and are related to the dynamical exponent z and the "roughness exponent" α characterizing the unperturbed flock dynamics. Using a well supported conjecture for the values of these two exponents, we obtain ν=2/3, γ=4/5 in d=2 and ν=1/4, γ=2/5 in d=3. These values are confirmed by our simulations.
Original language | English |
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Article number | 073039 |
Pages (from-to) | 1-14 |
Number of pages | 14 |
Journal | New Journal of Physics |
Volume | 18 |
DOIs | |
Publication status | Published - 20 Jul 2016 |
Bibliographical note
AcknowledgmentsWe have benefited from discussions with H Chaté and A Cavagna. We acknowledge support from the Marie Curie Career Integration Grant (CIG) PCIG13-GA-2013-618399. JT also acknowledges support from the SUPA distinguished visitor program and from the National Science Foundation through awards # EF-1137815 and 1006171, and thanks the University of Aberdeen for their hospitality while this work was underway. FG acknowledges support from EPSRC First Grant EP/K018450/1.
Keywords
- active matter
- flocking
- response theory
- emergent behavior
- renormalization group