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BP: Fachverband Biologische Physik
BP 13: Active Matter III (joint session DY/BP/CPP)
BP 13.1: Vortrag
Dienstag, 18. März 2025, 09:30–09:45, H47
From micro to macro: systematic coarse-graining of active particle models and implications on phase separation — •Sumeja Burekovic1, Filippo De Luca2, Cesare Nardini1,3, Ananyo Maitra4,5, and Michael E. Cates2 — 1CEA, Paris-Saclay, France — 2DAMTP, University of Cambridge, UK — 3LPTMC, Sorbonne Université, France — 4LPTM, CY Cergy Paris Université, France — 5LJP, Sorbonne Université, France
Significant insights into collective phenomena of active systems, such as phase separation, have been obtained through minimal field theories developed in a top-down manner. In contrast, the bottom-up approach seeks to link these continuum models to the microscopic dynamics of active particles, often formulated as Langevin equations for their position and orientation. This connection is typically achieved via explicit coarse-graining and allows active field theories to be expressed in terms of physically meaningful parameters. A major challenge in coarse-graining is the consistent elimination of irrelevant fast degrees of freedom to derive closed equations for the hydrodynamic variables or order parameters, such as the density field. We propose a systematic extension of standard homogenization/projection-operator techniques. As we show in minimal examples with few degrees of freedoms, our technique allows to go beyond the state of the art of homogenization in the mathematical literature. We then discuss the predictions of our coarse-graining methods for the large-scale phenomenology of non-aligning active particles, including cases in which microphase separation - rather than full phase separation - emerges due to activity.
Keywords: Motility-Induced Phase Separation; Coarse-graining; Active Particles; Stochastic averaging; Hydrodynamic limits