An improved result on Chern conjecture

Abstract

Let $X: M^n\to \mathbb S^{n+1}(1)$ be a closed minimal hypersurface with constant scalar curvature. Chern conjecture says that a closed minimal hypersurface with constant scalar curvature, $S\geq 2n$ if $S>n$, where $S$ is the squared norm of the second fundamental form. As a partial result, Peng-Terng \cite{pt1, pt2}, Yang-Cheng \cite{yc1, yc2, yc3} and Suh-Yang \cite{sy} obtained that if $S>n$, then $S>n+ \dfrac{3}n$. Recently, Chen \cite{c} has proved $S>n+\frac{26}{59}n$ if $S>n$. Since resolving Chern conjecture is a hard problem, as a midway for resolving Chern conjecture, one wants to prove $S>n+\frac12 n$ if $S>n$. In this paper, for $4\leq n\leq 13$, we give a positive solution for this midway problem. For general $n$, we prove that for a complete minimal hypersurface with constant scalar curvature, \[ S>\frac{10000000}{6869671}\,n >1.4556737869\,n>n+\dfrac{221}{485}n \] if $S>n$, which is better than the result of Chen \cite{c}.