# Regensburg 2019 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 20: Active Matter B (joint session DY/CPP)

### DY 20.5: Vortrag

### Dienstag, 2. April 2019, 15:00–15:15, H3

**Continuum model for active polar fluids with density variations** — •Vasco M. Worlitzer^{1}, Avraham Be'er^{2}, Gil Ariel^{3}, Markus Bär^{1}, Holger Stark^{4}, and Sebastian Heidenreich^{1} — ^{1}Department of Mathematical Modelling and Data Analysis, Physikalisch-Technische Bundesanstalt, 10597 Berlin, Germany — ^{2}Zuckerberg Institute for Water Research, The Jacob Blaustein Intitutes for Desert Research, Ben-Gurion University, Sede Boqer Campus, Midreshet Ben-Gurion, Israel — ^{3}Department of Mathematics, Bar-Ilan University, Ramat Gan, Israel — ^{4}Institute of Theoretical Physics, Technical University of Berlin, 10623 Berlin, Germany

Bacterial suspensions are intriguing examples for active polar fluids which exhibit large scale collective behavior from mesoscale turbulence to vortex lattices. For dense bacterial suspensions an effective fourth-order polar field theory was introduced modelling the collective dynamics in agreement with experimental findings [1,2]. However, in recent experiments of Bacillus subtilis suspensions anomalous velocity statistics and density variations are found which are not captured by the theory. In our contribution, we present a phenomenological theory for an active polar fluid with density and swimmer-velocity variations. We show that these variations result in an anomalous velocity statistics as observed in recent experiments [3].

[1] J Dunkel, S Heidenreich, K Drescher, HH Wensink, M Bär and RE Goldstein, Phys. Rev. Lett. 110 (2013) 228102. [2] S Heidenreich, J Dunkel, SHL Klapp and M Bär, Phys. Rev. E 94 (2016) 020601(R). [3] SD Ryan, G Ariel, A Be'er, Biophys J. (2016) 247.