IAS-2 Seminar: Symmetry breaking in active non-reciprocal systems

Kim Kreienkamp

Institute for Theoretical Physics, Technische Universität Berlin

Join us in person in Building 04.16, Room 2001

Non-reciprocal couplings significantly impact the dynamical behavior in 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 with completely symmetric repulsion. Using a combination of field theory and particle-based simulations, we identify two qualitatively distinct regimes of non-reciprocity-induced dynamics. In the regime of weak intra-species alignment, non-reciprocity leads to asymmetric clustering in which predominantly one of the two species forms clusters.

Notably, the asymmetric density dynamics is driven alone by non-reciprocal orientational couplings. In contrast, in the strongly coupled regime, the corresponding field theory exhibits exceptional points that have been associated with the emergence of chiral phases where the polarization direction rotates over time.

Our simulations confirm that spontaneous chirality arises at the particle level. In particular, we observe chimera-like states with coexisting locally synchronized and disordered regions and a peak of spontaneous chirality at coupling strengths associated with exceptional points. Our results highlight the diverse effects of non-reciprocity across different scales.