Symmetry breaking in active non-reciprocal systems
Kim Kreienkamp (TU Berlin)
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. Both the spontaneous chirality and entropy production rate peak at coupling
strengths associated with exceptional points. Our results highlight the diverse effects of non-reciprocity across different scales.