Classification of multi-solitons in one sense of time for the 5D energy-critical wave equation

Abstract

We classify the multi-solitons, in the positive sense of time, of the focusing energy-critical wave equation in space dimension $5$, more precisely the solutions $u(t,x)$ of the equation \[ \partial_t^2 u - Δu - |u|^{\frac 4{3}} u = 0, \quad (t,x)\in [T_0,\infty)\times {\mathbb R}^5, \] which satisfy the estimate \[ \left\|\nabla_{t,x} \left(u(t) - \sum_{k} W_k(t) \right) \right\|_{L^2} \lesssim t^{-\frac12^+} \quad \hbox{for all $t\gg 1$}. \] Here, $\{W_k{\}}_k$ is any given finite family of traveling waves, based on the explicit ground state solution \[ W(x) = \left(1+ \frac{|x|^2}{15}\right)^{-\frac32} \] with collinear two-by-two different velocities.