Classification without the bound on the squared second fundamental form

Classify complete self-shrinkers in arbitrary codimension with positive constant scalar curvature after removing the assumption that the squared norm S of the second fundamental form satisfies S≤1, including the higher-codimension product examples with S>1.

Background

The paper proves that every complete self-shrinker in arbitrary codimension with positive constant scalar curvature and S≤1 is isometric to a round sphere or a standard generalized cylinder. The restriction S≤1 is used to invoke the Cao–Li gap theorem. The authors note that higher-codimension products of round spheres and Euclidean factors provide examples with positive constant scalar curvature and S>1, so removing the bound requires a broader classification encompassing these examples.

References

Can the assumption S\le 1 be removed? As pointed out in Remark \ref{remark-S}, in higher codimension there exist product examples with S>1 and positive constant scalar curvature, so a complete classification must include such examples.

Complete Self-Shrinkers in Arbitrary Codimension with Positive Constant Scalar Curvature and \(S\le 1\)  (2609.19464 - Guo, 16 Sep 2026) in Section 6, Concluding remarks

Can one classify complete self-shrinkers with negative or sign-changing scalar curvature? The algebraic Lemma \ref{alg} uses the positivity of R in an essential way, and the negative case requires a different approach.

Complete Self-Shrinkers in Arbitrary Codimension with Positive Constant Scalar Curvature and \(S\le 1\)  (2609.19464 - Guo, 16 Sep 2026) in Section 6, Concluding remarks