Stable and Minimizing Cones in the Alt-Phillips Problem

Abstract: We study homogeneous solutions to the Alt-Phillips problem when the exponent $\gamma$ is close to 1. In dimension $d\ge3$, we show that the radial cone is minimizing when $\gamma$ is close to 1. In dimension $d \ge 4$, we construct an axially symmetric cone whose contact set has with positive density. We show that it is a global minimizer. It is analogous to the De Silva-Jerison \cite{DJ} cone for the Alt-Caffarelli functional which corresponds to exponent $\gamma=0$. The cone we construct bifurcates from another minimizing cone whose contact set has zero density, obtained as the trivial extension of the radial solution. This second cone is analogous to a quadratic polynomial solution in the classical obstacle problem which corresponds to exponent $\gamma=1$. In particular our results show that, when $\gamma<1$ is sufficiently close to 1, there are axis symmetric cones that exhibit the properties of both end point cases $\gamma=0$ and $\gamma=1$.