Stable self-similar blow up for energy subcritical wave equations

Abstract: We consider the semilinear wave equation [ \partial_t^2 \psi-\Delta \psi=|\psi|^{p-1}\psi ] for $1&lt;p\leq 3$ with radial data in $\R^{3}$. This equation admits an explicit spatially homogeneous blow up solution $\psi^T$ given by $\psi^T(t,x)=\kappa_p (T-t)^{-\frac{2}{p-1}}$ where $$T\&gt;0$$ and $\kappa_p$ is a $p$-dependent constant. We prove that the blow up described by $\psi<sup>T$ is stable against small perturbations in the energy topology. This complements previous results by Merle and Zaag. The method of proof is quite robust and can be applied to other self-similar blow up problems as well, even in the energy supercritical case.