Energy-critical semi-linear shifted wave equation on the hyperbolic spaces

Abstract

In this paper we consider a semi-linear, energy-critical, shifted wave equation on the hyperbolic space ${\mathbb{H}}^n$ with $3\le n\le 5$: \[ \partial_t^2 u - (Δ_{{\mathbb H}^n} + ρ^2) u = ζ|u|^{4/(n-2)} u, \quad (x,t)\in {\mathbb H}^n \times {\mathbb R}. \] Here $\zeta =\pm 1$ and $\rho =(n-1)/2$ are constants. We introduce a family of Strichartz estimates compatible with initial data in the energy space $H^{0,1}\times L^2({\mathbb{H}}^n)$ and then establish a local theory with these initial data. In addition, we prove a Morawetz-type inequality \[ \int_{-T_-}^{T_+} \int_{{\mathbb H}^n} \frac{ρ(\cosh |x|) |u(x,t)|^{2n/(n-2)}}{\sinh |x|} dμ(x) dt \leq n {\mathcal E}, \] in the defocusing case $\zeta =-1$, where $\mathcal{E}$ is the energy. Moreover, if the initial data are also radial, we can prove the scattering of the corresponding solutions by combining the Morawetz-type inequality, the local theory and a pointwise estimate on radial $H^{0,1}({\mathbb{H}}^n)$ functions.

20 pages, 2 figures