Soliton-soliton collisions in a generalized Zakharov system

The system of the nonlinear Schrödinger and dAlembert equations with Zakharov coupling is considered. This system admits both subsonic and transsonic solitons. The subjects of the work are symmetric soliton-soliton collisions in this model. First, the collision-induced emission of acoustic waves (in the dAlembert subsystem) is treated analytically for the case when the velocities of the solitons are much larger than their amplitudes. It is demonstrated that the acoustic losses are exponentially small unless the solitons velocities are much larger than the sound velocity. Next, the collision is simulated numerically in a general case. Two basic phenomena are observed. The collision of subsonic solitons always leads to their fusion into a breather, provided the system is sufficiently far from the integrable limit. The collision between the transsonic solitons gives rise to a multiple production of solitons (both subsonic and transsonic ones are produced), and the quasielastic character of the collision is recovered in the limit of large velocities.