Dresden 2026 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 11: Active Matter II (joint session DY/BP/CPP)
CPP 11.6: Talk
Monday, March 9, 2026, 16:15–16:30, ZEU/0160
Number fluctuations distinguish different self-propelling dynamics — •Tristan Cerdin1,2, Sophie Marbach2, and Carine Douarche1 — 1Université Paris-Saclay, CNRS, FAST, 91405, Orsay, France — 2CNRS, Sorbonne Université, Physicochimie des Electrolytes et Nanosystèmes Interfaciaux, F-75005 Paris, France
In nonequilibrium suspensions, static number fluctuations N in virtual observation boxes reveal remarkable structural properties, but the dynamic potential of N(t) signals remains unexplored. Here, we develop a theory to learn the dynamical parameters of self-propelled particle models from N(t) statistics.
Theoretical plots of the mean-squared number difference ⟨ Δ N2(t)⟩ exhibit 3 scaling regimes in time corresponding to the 3 regimes of self-propelled particles: diffusive, advective and effectively diffusive again at long times. By expanding the theory in each of these regimes, we recover limiting laws for the number fluctuations, which can be used in practice to quantify self-propulsion properties.
Additionally, unlike traditional trajectory analysis, N(t) statistics distinguish between models, by sensing subtle differences in reorientation dynamics that govern re-entrance events in boxes. This paves the way for quantifying advanced dynamic features in dense, out-of-equilibrium suspensions.
Keywords: Number Fluctuations; Active Brownian Particles; Run and Tumble; Coarse graining; Moment expansion