Dresden 2026 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 34: Focus Session: Fluids with Broken Time-Reversal Symmetry – Odd/Hall Viscosity Between Active Matter and Electron Flows

DY 34.9: Vortrag

Mittwoch, 11. März 2026, 12:00–12:15, ZEU/0160

Exceptional points, chirality and entropy production in nonreciprocal polar active matter — Kim L. Kreienkamp and •Sabine H. L. Klapp — Institut für Physik, Technische Universität Berlin, Germany

Non-reciprocal couplings significantly impact the collective dynamics of mixtures. A particularly striking consequence of such couplings is the spontaneous emergence of time-dependent phases that break parity-time symmetry. Here, we study a paradigmatic model of a non-reciprocal polar active mixture by combining field-theoretical analyses and particle-based simulations. When different species have opposing alignment tendencies, flocking states with spontaneously broken rotational symmetry transform into chiral states characterized by a rotating polarization direction. At the field-theoretical level, the transition to these parity-time-symmetry-breaking chiral states is indicated by so-called exceptional points. We demonstrate that these theoretical concepts have clear counterparts in particle-based systems [1]: we observe chimera-like states with coexisting locally synchronized and disordered regions, and find that both the spontaneous chirality and the entropy production rate [2] peak at coupling strengths corresponding to the exceptional points. Our results highlight the diverse effects of non-reciprocity across different scales.

[1] K. L. Kreienkamp and S. H. L. Klapp, Communications Physics 8, 307 (2025)

[2] K. L. Kreienkamp and S. H. L. Klapp, arXiv:2508.05209 (2025)

Keywords: nonreciprocal systems; active matter