Dispersive Estimates for Manifolds with one Trapped Orbit

Abstract

For a large class of complete, non-compact Riemannian manifolds, $(M,g)$, with boundary, we prove high energy resolvent estimates in the case where there is one trapped hyperbolic geodesic. As an application, we have the following local smoothing estimate for the Schr\"odinger propagator: \int_0^T || \rho_s e^{it(\Delta_g-V)} u_0 ||_{H^{1/2 - \epsilon}(M)}^2 dt \leq C_T || u_0 ||_{L^2(M)}^2, where $\rho_s(x) \in \Ci(M)$ satisfies $\rho_s = <\dist_g(x,x_0)>^{-s}$, $s> \half$, and $V \in \Ci(M)$, $0 \leq V \leq C$ satisfies $|\nabla V| \leq C <\dist(x,x_0)>^{-1-\delta}$ for some $\delta>0$. From the local smoothing estimate, we deduce a family of Strichartz-type estimates, which are used to prove two well-posedness results for the nonlinear Schr\"odinger equation. As a second application, we prove the following exponential local energy decay estimate for solutions to the wave equation when $\dim M = n \geq 3$ is odd and $M$ is equal to $\reals^n$ outside a compact set: \be \int_M |\psi \partial_t u |^2 + | \psi \nabla u |^2 dx} \leq C e^{-t/C} (||u(x,0)||_{H^{1+\epsilon}(M)}^2 + ||D_tu(x,0)||_{H^\epsilon(M)}^2), where $\psi \in \Ci(M)$, $\psi \equiv e^{-|x|^2}$ outside a compact set.