Emergent odd response in active chiral films
Abstract
Active chiral fluids can support an anomalous transport coefficient known as odd (or Hall) viscosity. Hydrodynamic descriptions of such fluids typically introduce odd viscosity phenomenologically. How such a response emerges from specific microscopic interactions remains incompletely understood. Here, building on classical shear rheology, we microscopically derive an odd rheological response in active chiral films: thin layers of torque-exerting, elongated particles anchored to a no-slip surface. A canonical realization of such a film is the bacterial carpet, in which flagellated bacteria are tethered head-down to a solid surface while their flagella remain free to spin and inject angular momentum into the surrounding fluid. Using a Smoluchowski kinetic theory for the orientational dynamics of these anchored particles, we derive their stress response to an imposed shear flow. We reveal that shear-induced reorientation leads to a flow-aligned polarization and a transverse surface traction from which the odd-viscosity tensor follows in closed form. This approach stands in contrast with existing microscopic theories, in which the axis of torque injection is insensitive to the flow rather than set by it. Numerical solutions of the kinetic theory further highlight saturation of the transverse traction at strong shear, driven by this orientation dynamics -- signaling departure from linear response. Our results demonstrate how odd viscosity can emerge self-consistently as a coarse-grained rheological signature of active fluid-structure interaction and establish active chiral films as a new controllable setting for odd hydrodynamics.
Related
- Emergent hydrodynamics of chiral active fluids: vortices, bubbles and odd diffusion
- Breakdown of Emergent Chiral Order and Defect Chaos in Nonreciprocal Flocks
- Emergent Chiral Metal Phase in Compressible Quantum Hall Fluids
- Emergent Self-Organisation of Intelligent Active Particles
- Odd slip at chiral active surfaces
BibTeX
@misc{chahal2026emergent,
title = {{Emergent odd response in active chiral films}},
author = {Seema Chahal and Naveen Kumar D and Brato Chakrabarti},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2607.17717},
eprint = {2607.17717},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.17717},
}
RIS
TY - UNPB
TI - Emergent odd response in active chiral films
AU - Seema Chahal
AU - Naveen Kumar D
AU - Brato Chakrabarti
PY - 2026
DA - 2026/11/02
PB - arXiv
DO - 10.48550/arxiv.2607.17717
UR - https://arxiv.org/abs/2607.17717
AB - Active chiral fluids can support an anomalous transport coefficient known as odd (or Hall) viscosity. Hydrodynamic descriptions of such fluids typically introduce odd viscosity phenomenologically. How such a response emerges from specific microscopic interactions remains incompletely understood. Here, building on classical shear rheology, we microscopically derive an odd rheological response in active chiral films: thin layers of torque-exerting, elongated particles anchored to a no-slip surface. A canonical realization of such a film is the bacterial carpet, in which flagellated bacteria are tethered head-down to a solid surface while their flagella remain free to spin and inject angular momentum into the surrounding fluid. Using a Smoluchowski kinetic theory for the orientational dynamics of these anchored particles, we derive their stress response to an imposed shear flow. We reveal that shear-induced reorientation leads to a flow-aligned polarization and a transverse surface traction from which the odd-viscosity tensor follows in closed form. This approach stands in contrast with existing microscopic theories, in which the axis of torque injection is insensitive to the flow rather than set by it. Numerical solutions of the kinetic theory further highlight saturation of the transverse traction at strong shear, driven by this orientation dynamics -- signaling departure from linear response. Our results demonstrate how odd viscosity can emerge self-consistently as a coarse-grained rheological signature of active fluid-structure interaction and establish active chiral films as a new controllable setting for odd hydrodynamics.
ER -