Rotating waves in nonlinear media and critical degenerate Sobolev inequalities

We investigate the presence of rotating wave solutions of the nonlinear wave equation 2 t vv + mv = |v| p-2 v in B, where B N is the unit ball, complemented with Dirichlet boundary conditions on B. Depending on the prescribed angular velocity of the rotation, this leads to a Dirichlet problem for a semilinear elliptic or degenerate elliptic equation.We show that this problem is governed by an associated critical degenerate Sobolev inequality in the half-space.After proving this inequality and the existence of associated extremal functions, we then deduce necessary and sufficient conditions for the existence of ground state solutions.Moreover, we analyze under which conditions on , m and p these ground states are nonradial and therefore give rise to truly rotating waves.Our approach carries over to the corresponding Dirichlet problems in an annulus and in more general Riemannian models with boundary, including the hemisphere.We briefly discuss these problems and show that they are related to a larger family of associated critical degenerate Sobolev inequalities.1. Introduction 307 2. A family of degenerate Sobolev inequalities 315 3. A degenerate Sobolev inequality on B 327 4. The variational setting for and main results on ground state solutions 332 5.The case of an annulus 348 6. Riemannian models 351 Appendix A. Boundedness of solutions 356 Appendix B. Round metric on spheres in angular coordinates 357