Propagation of singularities for gravity-capillary water waves

Abstract

We obtain two results of propagation for solutions to the gravity-capillary water wave system. First we show how oscillations and the spatial decay propagate at infinity; then we show a microlocal smoothing effect under the non-trapping condition of the initial free surface. These results extends the works of Craig, Kappeler and Strauss, Wunsch and Nakamura to quasilinear dispersive equations. We also prove the existence of gravity-capillary water waves in weighted Sobolev spaces. Such solutions have asymptotically Euclidean free surfaces. To obtain these results, we generalize the paradifferential calculus of Bony to weighted Sobolev spaces and develop a semiclassical paradifferential calculus. We also introduce a new family of wavefront sets -- the quasi-homogeneous wavefront sets, which is a generalization, at least in the Euclidean geometry, the wavefront sets of Hörmander, the scattering wavefront sets of Melrose, the quadratic scattering wavefront sets of Wunsch and the homogeneous wavefront sets of Nakamura.