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Structure and memory control self-diffusion in active matter

Akinlade Akintunde1 and Stewart A. Mallory1,2,*

  • *Contact author: sam7808@psu.edu
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Phys. Rev. E 114, 014115 – Published 10 July, 2026

DOI: https://doi.org/10.1103/sg5l-6zsh

Abstract

Despite extensive progress in characterizing the emergent behavior of active matter, the microscopic origins of self-diffusion in interacting active systems remain poorly understood. Here, we develop a framework that quantitatively links self-diffusion to collisional forces and their temporal correlations in active fluids. We show that transport is governed by two contributions: an equal-time suppression of motion arising from anisotropic collisional forces, and a memory correction associated with the temporal persistence of these forces. Together, these effects yield an exact expression for the self-diffusivity in terms of measurable force statistics and correlation times. We apply this framework to purely repulsive active Brownian particles and find that self-diffusion is always reduced as a function of packing fraction and activity. We identify the regimes in which equal-time force fluctuations and collisional memory dominate and how their relative contributions vary with activity and packing fraction. Our results establish a direct connection between microscopic force correlations and macroscopic transport, providing a general mechanical perspective for interpreting self-diffusion in active matter.

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Outline

Information

Phys. Rev. E 114, 014115– Published 10 July, 2026
  • Received 19 January 2026
  • Revised 29 March 2026
  • Accepted 17 June 2026
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