Information transfer, flocking and defects in a non-reciprocal XY model*

We study the classical dynamics of a lattice of XY spins, i.e., planar rotors with inertia and damping, characterized by a unit vector p_i  at site i, where the torque on the i ^th rotor due to the j ^th depends on whether site j is ahead or astern of i, as defined by the direction of p_i. We study analytically and numerically the consequences [Dadhichi et al., Phys Rev E 101, 052601 (2020)] of this non-mutuality of interaction, including self-advection of the orientation and the resulting bend waves of flocking models, directed information transfer and, at large enough asymmetry, a bending instability and spatiotemporal chaos.