We study the asymptotic response of polar ordered active fluids ('flocks') to small external aligning fields h. The longitudinal susceptibility chi(parallel to) diverges, in the thermodynamic limit, like h(-nu) as h -> 0. In finite systems of linear size L, chi(parallel to) saturates to a value similar to L-gamma. The universal exponents nu and gamma depend only on the spatial dimensionality d, and are related to the dynamical exponent z and the 'roughness exponent' alpha characterizing the unperturbed flock dynamics. Using a well supported conjecture for the values of these two exponents, we obtain nu = 2/3, gamma = 4/5 in d = 2 and nu = 1/4, gamma = 2/5 in d = 3. These values are confirmed by our simulations.

Leading birds by their beaks: the response of flocks to external perturbations

Ginelli F;
2016-01-01

Abstract

We study the asymptotic response of polar ordered active fluids ('flocks') to small external aligning fields h. The longitudinal susceptibility chi(parallel to) diverges, in the thermodynamic limit, like h(-nu) as h -> 0. In finite systems of linear size L, chi(parallel to) saturates to a value similar to L-gamma. The universal exponents nu and gamma depend only on the spatial dimensionality d, and are related to the dynamical exponent z and the 'roughness exponent' alpha characterizing the unperturbed flock dynamics. Using a well supported conjecture for the values of these two exponents, we obtain nu = 2/3, gamma = 4/5 in d = 2 and nu = 1/4, gamma = 2/5 in d = 3. These values are confirmed by our simulations.
2016
Kyriakopoulos, N; Ginelli, F; Toner, J
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11383/2081559
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