Bright solitary waves in a Bose-Einstein condensate and their   interactions
  We examine the dynamics of two bright solitary waves with a negative nonlinear term. The observed repulsion between two solitary waves -- when these are in an antisymmetric combination -- is attributed to conservation laws. Slight breaking of parity, in combination with weak relaxation of energy, leads the two solitary waves to merge. The effective repulsion between solitary waves requires certain nearly ideal conditions and is thus fragile. 
K. Karkkainen, A. D. Jackson, G. M. Kavoulakis