On the interaction of spiral waves in non-equilibrium media

We show that the asymptotic interaction of spirals in two-dimensionally oscillating continuous media falls off exponentially and can be attractive as well as repulsive depending on the parameters of the system but not on the topological charges. The exponent is in qualitative agreement with simulations. For moderate distances the simulations show that spirals may form a stable bound state. Pairs with opposite topological charges drift with constant velocity and like-charged spirals rotate around each other with constant frequency. This is in contrast with the stationary (non-oscillating) case, where the interaction of vortices (or dislocations) is long range and monotonical and depends on topological charges.