Stability and excitations of solitons in 2D Bose-Einstein condensates
  The small oscillations of solitons in 2D Bose-Einstein condensates are investigated by solving the Kadomtsev-Petviashvili equation which is valid when the velocity of the soliton approaches the speed of sound. We show that the soliton is stable and that the lowest excited states obey the same dispersion law as the one of the stable branch of excitations of a 1D gray soliton in a 2D condensate. The role of these states in thermodynamics is discussed. 
S. Tsuchiya, F. Dalfovo, C. Tozzo, and L. Pitaevskii