Radial pinching and topological rigidity for free boundary Gaussian $f$-minimal submanifolds

Abstract

Let $M^k\subset {\overline{B}}_R^N$ be a smooth compact connected orientable free boundary $f_c$-minimal submanifold of the closed Euclidean ball, where $f_c(x)=c|x{|}^2/2$ and $c\ge 0$. Assume that $c{R}^2\le k$ and $|A_{x^{\perp }}{|}^2\le 1+\frac{1}{k-1}(1-c|x^{\perp }{|}^2{)}^2$, where $A_{x^{\perp }}(X,Y)=⟨x^{\perp },A(X,Y)⟩$. We prove that $M$ is diffeomorphic either to $D^k$ or to $S^1\times D^{k-1}$; strict pinching yields the disk. The proof uses Hessian convexity of the squared-distance function, a nullity estimate along its minimum set, and a sublevel-set argument. In dimension two and codimension one, the non-disk branch is rotationally symmetric. We also construct a local family of embedded rotational examples for small $c\ge 0$, with the $c=0$ member equal to the critical catenoid.