Events

Date: 3 December 2025   Time: 14:00 - 15:00

Location: Online via the Teams link below

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 then demonstrate that these theoretical concepts have clear counterparts in particle-based systems: we observe chimera-like states with coexisting locally synchronized and disordered regions, and find that both the spontaneous chirality and the entropy production rate peak at coupling strengths corresponding to the exceptional points. Our results highlight the diverse effects of non-reciprocity across different scales.

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