On the Minkowski inequality near the sphere

Abstract

We construct a sequence $\{Σ_\ell\}_{\ell=1}^\infty$ of closed, axially symmetric surfaces $Σ_\ell\subset \mathbb{R}^3$ that converges to the unit sphere in $W^{2,p}\cap C^1$ for every $p\in[1,\infty)$ and such that, for every $\ell$, $$ \int_{Σ_{\ell}}H_{Σ_\ell}-\sqrt{16\,π\,|Σ_{\ell}|}<0 $$ where $H_{Σ_\ell}$ is the mean curvature of $Σ_\ell$. This shows that the Minkowski inequality with optimal constant fails even for perturbations of a round sphere that are small in $W^{2,p}\cap C^1$ unless additional convexity assumptions are imposed.