  We investigate the properties of finite energy travelling waves to the
nonlinear Schrodinger equation with nonzero conditions at infinity for a wide
class of nonlinearities. In space dimension two and three we prove that
travelling waves converge in the transonic limit (up to rescaling) to ground
states of the Kadomtsev-Petviashvili equation. Our results generalize an
earlier result of F. Bethuel, P. Gravejat and J-C. Saut for the two-dimensional
Gross-Pitaevskii equation, and provide a rigorous proof to a conjecture by C.
Jones and P. H. Roberts about the existence of an upper branch of travelling
waves in dimension three.
