Morse index computation for radial solutions of the {Hé}non problem in the disk

Abstract

We compute the Morse index $\text{m}(u_p)$ of any radial solution $u_p$ of the semilinear problem: \begin{equation} \label{problemaAbstract}\tag{P} \left\{ \begin{array}{lr} -Δu=|x|^α|u|^{p-1}u & \mbox{in } B\\ u=0 & \mbox{ on }\partial B \end{array} \right. \end{equation} where $B$ is the unit ball of ${\mathbb{R}}^2$ centered at the origin, $\alpha \ge 0$ is fixed and $p>1$ is sufficiently large. In the case $\alpha =0$, i.e. for the \emph{Lane-Emden problem}, this leads to the following Morse index formula \[\textsf{m}(u_{p}) = 4m^{2}-m-2, \] for $p$ large enough, where $m$ is the number of nodal domains of $u$.