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A collisional model of odd fluids: from Boltzmann equation to chiral hydrodynamics

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arxiv 2508.12944 v1 pith:FBRP5PIT submitted 2025-08-18 cond-mat.soft cond-mat.stat-mech

A collisional model of odd fluids: from Boltzmann equation to chiral hydrodynamics

classification cond-mat.soft cond-mat.stat-mech
keywords modelfluidsresponsetheorycoefficientsmicroscopicbeenboltzmann
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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When the time-reversal and parity symmetries in a fluid are broken, transverse transport coefficients can arise in response to perturbations, an example being odd viscosity. We refer to these systems as odd fluids. While much progress has been made in the continuum theory of odd-viscous fluids, and non-collisional models for odd viscous fluids have been proposed, a classical microscopic description in which the transverse responses originate from collisions is lacking. In this paper, we show that a dilute granular gas of rough and inelastic particles driven by a constant torque is a minimal microscopic model of an odd fluid. By applying the methods of Boltzmann kinetic theory, we obtain a hydrodynamic description of the microscopic model. Then, using the method of adiabatic elimination, we numerically compute all the response coefficients of the model, explicitly showing that the model has many odd response terms. Our theory predicts that certain odd response coefficients can change sign even when the direction of the external torque is fixed. While we choose a particular case, the procedure we present can be applied to any collisional model. We also present a semi-quantitative method to determine the hydrodynamic variables of the theory by observing the eigenvalue spectrum of the linear collision operator.

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Cited by 5 Pith papers

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  1. Steady base states in a two-dimensional chiral fluid. The chiral Stokes cavity

    cond-mat.soft 2026-07 conditional novelty 7.0

    Enforcing angular-momentum conservation without stress symmetry yields a 2D chiral hydrodynamics in which every odd channel is the 90° rotation of a Newtonian one, and confined steady flows reduce to a modified Helmho...

  2. Kinetic and Hydrodynamic Theories of Chiral Intruder Dynamics in Nonequilibrium Baths

    cond-mat.stat-mech 2026-07 conditional novelty 7.0

    An intruder in a chiral nonequilibrium bath acquires shape-chirality ratchet torques in the dilute limit and edge-current-generated odd drag and torque in the dense limit.

  3. Chiral Dynamics of an Intruder across Dilute and Hydrodynamic Regimes

    cond-mat.stat-mech 2026-07 conditional novelty 7.0

    A kinetic-to-hydrodynamic derivation shows intruder shape sets chiral transport via boundary integrals in dilute baths and via torque-density edge currents in dense baths.

  4. Odd fluids from chiral cellular automata

    cond-mat.stat-mech 2026-06 unverdicted novelty 7.0

    A parity-breaking chiral extension of the FHP cellular automaton is constructed and shown to yield hydrodynamics with odd viscosity, verified through Poiseuille-flow simulations.

  5. Emergent odd response in active chiral films

    cond-mat.soft 2026-07 conditional novelty 6.0

    An active chiral film of anchored spinning rods has a derived Hall-viscosity coefficient η_o = 3A/32 in weak shear, with the transverse traction saturating at high shear.