Title: Dispersion for the wave equation outside a ball and counterexamples,
Abstract: The purpose of this note is to prove dispersive estimates for the wave
equation outside a ball in R^d. If d = 3, we show that the linear flow
satisfies the dispersive estimates as in R^3. In higher dimensions d $\ge$ 4 we
show that losses in dispersion do appear and this happens at the Poisson spot.