Special Seminar


Tuesday, May 28, 2024 - 2:00pm to 5:45pm


ISEB 1010

Talk Schedule (each talk 30-35 minutes)

2:00 PM   Alex Mramor (University of Copenhagen)

2:45 PM   Kai-Wei Zhao (Notre Dame)

3:30 PM   Hongyi Sheng (UC San Diego)

4:15 PM   Tin Yau Tsang (New York University)

5:00 PM   Xiaolong Li (Wichita State University)



Speaker: Alex Mramor (University of Copenhagen)
Title: On the Unknottedness of Self Shrinkers
Abstract: The mean curvature flow, the natural analogue of the heat equation in submanifold geometry, often develops singularities and roughly speaking these singularities are modeled on self shrinkers, which are surfaces that give rise to mean curvature flows that move by dilations. it happens that self shrinkers are minimal surfaces in a metric which, while poorly behaved, is Ricci positive in a certain sense so it is natural, for instance, to ask what type of qualities shrinkers have in common with minimal surfaces in the round 3-sphere. Inspired by an old work of Lawson on such surfaces in this talk we discuss some unknottedness results for self shrinkers in R3, some of which are joint work with S. Wang.


Speaker: Kai-Wei Zhao (Notre Dame)
Title: Uniqueness of Tangent Flows at Infinity for Finite-Entropy Shortening Curves
Abstract: Curve shortening flow is, in compact case, the gradient flow of arc-length functional. It is the simplest geometric flow and is a special case of mean curvature flow. The classification problem of ancient solutions under some geometric conditions can be view as a parabolic analogue of geometric Liouville theorem. The previous results technically reply on the assumption of convexity of the curves. In the ongoing project joint with Kyeongsu Choi, Donghwi Seo, and Weibo Su, we replace it by the boundedness of entropy, which is a measure of geometric complexity defined by Colding and Minicozzi. In this talk, we will prove that an ancient smooth curve shortening flow with finite-entropy embedded in R2 has a unique tangent flow at infinity. To this end, we show that its rescaled flows backwardly converge to a line with multiplicity m≥3 exponentially fast in any compact region, unless the flow is a shrinking circle, a static line, a paper clip, or a translating grim reaper. In addition, we figure out the exact numbers of tips, vertices, and inflection points of the curves at negative enough time. Moreover, the exponential growth rate of graphical radius and the convergence of vertex regions to grim reaper curves will be shown.


Speaker: Hongyi Sheng (UC San Diego)
Title: Localized Deformations and Gluing Constructions in General Relativity
Abstract: Localized deformations play an important role in gluing constructions in general relativity. In this talk, we will review some recent localized deformation theorems and their applications regarding rigidity and non-rigidity type results.


Speaker: Tin Yau Tsang (New York University)
Title: Mass for the Large and the Small
Abstract: The positive mass theorem concerns the mass of large manifolds. In this talk, we will first review the proofs by Schoen and Yau, then the proof by Witten. Combining these with their recent generalisations turns out to help us understand the mass of small manifolds.


Speaker: Xiaolong Li (Wichita State University)
Title: Recent Developments on the Curvature Operator of the Second Kind
Abstract: In this talk, I will first introduce the curvature operator of the second kind and talk about the resolution of Nishikawa's conjecture by Cao-Gursky-Tran, myself, and Nienhaus-Petersen-Wink. Then I will talk about some ongoing research with Gursky concerning negative lower bounds of the curvature operator of the second kind. Along the way, I will mention some interesting problems.