Clustering and absorbing-state transition for active particles driven by nematic turn-towards/turn-away interactions

Active matter systems with nonreciprocal interactions offer new routes to nonequilibrium self-organization and collective behavior. In recent work, we showed that activity-induced hydrodynamic interactions can lead to the formation of immotile ordered clusters in systems of discoidal microswimmers with non-axisymmetric actuation. This tendency to cluster drives the system into a dynamically arrested absorbing state (Thambi and Uspal, Phys. Rev. Fluids, 2025). Here, we ask whether this phenomenon is specific to hydrodynamics or more broadly generic. We reproduce the clustering and arrest in a minimal “dry” model by using two pairwise interactions: isotropic repulsion, and nonreciprocal torques that drive alignment of a particle’s propulsion axis with the axis connecting the particle centers. These interactions, obtained as an idealized approximation of the fluid-mechanical equations, closely resemble those reported in Zhang et al., Nat. Phys, 2022. A crucial distinction, however, is that the torque in our model has nematic symmetry, promoting both “turning towards” and “turning away.” We investigate the basic character of the absorbing state transition, and also address whether the absorbing state can exhibit hyperuniformity.