ICMCS seminar - Insertion geometry in repulsive active matter

Title: Insertion geometry in repulsive active matter

Abstract: Living and biological systems are typically found in, or are proximal to, nonequilibrium environments. Indeed, much of this nonequilibriumness arises from the energy conversion of individual constituents which, when coupled with many-body interactions, results in striking collective behaviour. Such systems are the focus of a growing field of statistical physics called active matter. As one can imagine, the far-from-equilibrium behaviour of active matter presents several serious challenges to the equilibrium framework of thermodynamics. Here, in an effort to bridge these problems, we explore (for the first time) the stochastic geometry of active matter. This stochastic geometry, e.g., the averaged room to accommodate another sphere, relates exactly to the equation of state for equilibrium hard spheres. We here extend this idea to active systems by analysing the insertion space for repulsive active particles in one and two dimensions using both on- and off-lattice models. In 1D we derive closed-form expressions for the mean insertion cavity size, cavity number, and total insertion volume, all in excellent agreement with simulations. Strikingly, activity increases the total insertion volume and tends to keep the insertion space more connected. These results provide the first quantitative foundation for the stochastic geometry of active matter, and opens up a new route to building a thermodynamics of active and living systems.

Refs: Insertion space in repulsive active matter, L. K. Davis* & K. Proesmans arXiv 2509.08131 (2025)

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Meeting ID: 812 1147 0751
Passcode: ICMCS123