Bound states of topological defects in parametrically excited capillary ripples

Bound states of topological defects arising at parametric excitation of waves on the surface of a vertically vibrating thin layer of viscous fluid are investigated theoretically and in experiments. Stably existing bound states of two topological defects having like charges are observed. The distance between the topological defects is found to depend on supercriticality and on the depth of the liquid layer. Analysis of the phase field of the bound states of topological defects revealed quadrupolar components. An approximate theory has been constructed that allows one to calculate the phase fields of bound states and determine the dependence of the distance between the defects on governing parameters. It is shown that theoretical calculations give a correct explanation of data obtained in the experiments.