Fill-Ins of Tori with Scalar Curvature Bounded from Below

Abstract: Let $\gamma$ be a Riemannian metric on $\Sigma = S^1 \times T^{n-2}$, where $3 \leq n \leq 7$. Consider $\Omega = B^2 \times T^{n-2}$ with boundary $\partial \Omega = \Sigma$, and let $g$ be a Riemannian metric on $\Omega$ such that the scalar curvature $R_g \geq -n(n - 1)$ and $g|_{\partial \Omega} = \gamma$. Assuming the mean curvature of $\partial \Omega$ with respect to the outward normal is positive, we establish that the total mean curvature of $\partial \Omega$ is bounded from above by a constant depending only on $n$ and $\gamma$. Furthermore, we compute the sharp constant for this estimate when $\gamma$ is a flat metric. This result resolves a special case of a conjecture by Gromov concerning total mean curvature of fill-in with scalar curvature bounded from below. The proof combines techniques developed by Shi-Tam, Shi-Wang-Wei, as well as recent work by Brendle-Hung on the systolic inequality.