Symmetry breaking in active non-reciprocal systems
Abstract:
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.