The stability of the symmetric two-spiral state against asymmetric perturbations is investigated. It is shown that the the bound states are always unstable against a spontaneous breaking of symmetry, which leads to the formation of states with one dominant spiral. The existence and the stability of lattices of topological defects are discussed.

• Received 8 March 1993

DOI:https://doi.org/10.1103/PhysRevE.48.R9