Emergent hydrodynamics of chiral active fluids: vortices, bubbles and odd diffusion
Abstract
Starting from a microscopic multiparticle Langevin equation, we obtain a hydrodynamic description in terms of density and momentum fields for chiral active particles interacting via standard repulsive and nonlocal odd forces. These odd interactions are reciprocal but non-conservative: they are non-potential forces, as they act perpendicular to the vector joining any pair of particles. As a result, the torques that two particles exert on one another are non-reciprocal. The ensuing macroscopic continuum description consists of a continuity equation for the density and a generalized compressible Navier–Stokes equation for the fluid velocity. The latter includes a chirality-induced torque density term and an odd viscosity contribution. Our theory predicts the emergence of odd diffusivity, edge currents, and is consistent with an inhomogeneous phase—characterized by bubble-like structures—recently observed in simulations. Specifically, the theory exhibits a linear instability arising from the interplay between odd viscosity and torque density, and admits steady-state inhomogeneous solutions featuring bubbles and vortices, in qualitative agreement with numerical simulations. Our findings can be tested experimentally in systems of granular spinners or rotating microorganisms suspended in a fluid.
Related
- Minimal superfluid vortices in chiral perturbation theory
- Emergent Conformal Symmetry on Superfluid Vortices in Two-Color QCD and Pseudoreal Gauge Theories
- Metastability and nucleation of bubbles in active chiral systems
- Confined Riesz gas: From Newtonian Dynamics to Emergent Hydrodynamics
- Relativistic Covariance from Hamiltonian Hydrodynamics in the Chiral Limit
BibTeX
@article{marconi2026emergent,
title = {{Emergent hydrodynamics of chiral active fluids: vortices, bubbles and odd diffusion}},
author = {Umberto Marini Bettolo Marconi and Alessandro Petrini and Raphael Maire and Lorenzo Caprini},
journal = {New Journal of Physics},
year = {2026},
month = nov,
doi = {10.1088/1367-2630/ae6c55},
eprint = {2601.19432},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05853660v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Emergent hydrodynamics of chiral active fluids: vortices, bubbles and odd diffusion
AU - Umberto Marini Bettolo Marconi
AU - Alessandro Petrini
AU - Raphael Maire
AU - Lorenzo Caprini
PY - 2026
DA - 2026/11/05
JO - New Journal of Physics
DO - 10.1088/1367-2630/ae6c55
UR - https://hal.science/hal-05853660v1
AB - Starting from a microscopic multiparticle Langevin equation, we obtain a hydrodynamic description in terms of density and momentum fields for chiral active particles interacting via standard repulsive and nonlocal odd forces. These odd interactions are reciprocal but non-conservative: they are non-potential forces, as they act perpendicular to the vector joining any pair of particles. As a result, the torques that two particles exert on one another are non-reciprocal. The ensuing macroscopic continuum description consists of a continuity equation for the density and a generalized compressible Navier–Stokes equation for the fluid velocity. The latter includes a chirality-induced torque density term and an odd viscosity contribution. Our theory predicts the emergence of odd diffusivity, edge currents, and is consistent with an inhomogeneous phase—characterized by bubble-like structures—recently observed in simulations. Specifically, the theory exhibits a linear instability arising from the interplay between odd viscosity and torque density, and admits steady-state inhomogeneous solutions featuring bubbles and vortices, in qualitative agreement with numerical simulations. Our findings can be tested experimentally in systems of granular spinners or rotating microorganisms suspended in a fluid.
SN - 1367-2630
ER -