Hypersurfaces of $\mathbb{S}^2\times\mathbb{S}^2$ with constant sectional curvature

TL;DR

This paper classifies hypersurfaces in 22 with constant sectional curvature, showing they are related to minimal hypersurfaces and solutions of the sinh-Gordon equation, with a complete classification for constant mean curvature cases.

Contribution

It proves that the only constant sectional curvature in 22 hypersurfaces is 2 and establishes a link to the sinh-Gordon equation, providing a full classification.

Findings

Constant sectional curvature only 2

Hypersurfaces are parallel to minimal hypersurfaces with C=0

Complete classification for constant mean curvature hypersurfaces

Abstract

In this paper, we classify the hypersurfaces of $\mathbb{S}^2\times\mathbb{S}^2$ with constant sectional curvature. By applying the so-called Tsinghua principle, which was first discovered by the first three authors in 2013 at Tsinghua University, we prove that the constant sectional curvature can only be $\frac{1}{2}$ and the product angle function $C$ defined by Urbano is identically zero. We show that any such hypersurface is a parallel hypersurface of a minimal hypersurface in $\mathbb{S}^2\times\mathbb{S}^2$ with $C=0$, and we establish a one-to-one correspondence between the involving minimal hypersurface and the famous ``sinh-Gordon equation'' $$ (\frac{\partial^2}{\partial u^2}+\frac{\partial^2}{\partial v^2})h =-\tfrac{1}{\sqrt{2}}\sinh(\sqrt{2}h). $$ As a byproduct, we give a complete classification of the hypersurfaces of $\mathbb{S}^2\times\mathbb{S}^2$ with constant mean curvature and constant product angle function $C$.