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Chiral active fluids: Insights from the total momentum
Tomer Markovich1,2, Tom C Lubensky3
1Tel Aviv University, School of Mechanical Engineering, Tel Aviv 69978, Israel.
Physical Review. E
|October 21, 2025
Summary
Chiral active materials exhibit distinct dynamics due to particle rotation. Their total momentum differs from center-of-mass momentum, requiring new models beyond equilibrium fluid descriptions for accurate analysis.
Area of Science:
- Physics
- Materials Science
- Soft Matter Physics
Background:
- Chiral active materials microscopically break time-reversal and parity symmetries.
- This asymmetry often arises from particle rotation, driving systems far from equilibrium.
Purpose of the Study:
- To investigate the relationship between center-of-mass (c.m.) momentum and total momentum in chiral active materials.
- To demonstrate the insufficiency of c.m. dynamics for describing these systems and establish a new theoretical framework.
Main Methods:
- Theoretical analysis of momentum dynamics in chiral active matter.
- Comparison of c.m. stress and total momentum in non-equilibrium systems versus equilibrium fluids.
Main Results:
- Nonvanishing spin angular momentum creates a distinction between c.m. momentum and total momentum.
- Center-of-mass dynamics alone are inadequate for fully describing chiral active material behavior.
Conclusions:
- The total momentum, experimentally accessible, imposes symmetry constraints on stress tensor formulation.
- This leads to a relationship between central-force and spin-spin interactions, limiting odd viscosities to Hall viscosity and odd pressure.
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