# BPCPPDYSOE21 – wissenschaftliches Programm

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# BP: Fachverband Biologische Physik

## BP 19: Active Matter 2 - organized by Carsten Beta (Potsdam), Andreas Menzel (Magdeburg) and Holger Stark (Berlin) (joint session DY/BP/CPP)

### BP 19.1: Vortrag

### Dienstag, 23. März 2021, 11:00–11:20, DYa

**Mesoscale turbulence and dynamical clustering in active polar fluids** — •Vasco Marius Worlitzer^{1}, Gil Ariel^{2}, Avraham Be'er^{3}, Holger Stark^{4}, Markus Bär^{1}, and Sebastian Heidenreich^{1} — ^{1}Department of Mathematical Modelling and Data Analysis, Physikalisch-Technische Bundesanstalt, Abbestrasse 2-12, 10587 Berlin — ^{2}Department of Mathematics, Bar-Illan University, Ramat Gan 52000, Israel — ^{3}Zuckerberg Institute for Water Research of the Negev, Sede Boqer Campus 84900 Midreshet Ben-Gurion, Israel — ^{4}Institute of Theoretical Physics, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin

Bacterial suspensions are fascinating examples for active polar fluids which exhibit large scale collective behavior ranging from polar and disordered states to so-called mesoscale turbulence and vortex lattices. Previous approaches take into account the self-propulsion of bacteria and an effective polar-alignment interaction but assume for simplicity a constant density. Comparison with experiments showed that this modelling approach is successful, to some extent, in a relatively narrow regime corresponding to wild-type swarms in which density is indeed approximately constant and velocity distributions are Gaussian. We seek a unified model that can explain the observed phenomena across the entire phase space of swarming bacteria. To this end, we present a continuum model that allows variations in density. The model predicts new dynamical regimes, such as mixed states with coexisting vortex patterns and dynamical clusters, obeying anomalous statistics, similar to experimental observations.