Structure Theory of Parabolic Nodal and Singular Sets

Speaker: 

Robert Koirala

Institution: 

UC San Diego

Time: 

Tuesday, April 21, 2026 - 3:00pm to 4:00pm

Host: 

Location: 

340P

We will discuss new estimates for the size and structure of the nodal set $\{u=0\}$ and the singular set $\{u=|\nabla u|=0\}$ of solutions to parabolic inequalities with parabolic Lipschitz coefficients. In particular, we show that almost all of these sets are covered by regular parabolic Lipschitz graphs, with quantitative control, and that both satisfy parabolic Minkowski bounds depending only on a doubling quantity at a point. Many of these results are new even in the case of the heat equation on $\mathbb{R}^n\times \mathbb{R}$. This is joint work with Max Hallgren and Zilu Ma.

Flying wing construction of steady Ricci solitons

Speaker: 

Pak-Yeung Chan

Institution: 

National Tsing Hua University

Time: 

Tuesday, March 31, 2026 - 3:00pm to 4:00pm

Host: 

Location: 

340P Rowland Hall

Ricci solitons are generalizations of the Einstein manifolds and are self similar solutions to the Ricci flow. In particular, steady Ricci solitons are eternal solutions to the Ricci flow. In this talk, we will discuss the flying wing construction of some Kahler and Riemannian steady Ricci solitons of nonnegative curvature. This is based on joint work with Ronan Conlon and Yi Lai, as well as with Yi Lai and Man-Chun Lee.

Classification of Ancient Finite-Entropy Curve Shortening Flows

Speaker: 

Kai-Wei Zhao

Institution: 

UCI

Time: 

Tuesday, April 28, 2026 - 4:00pm to 5:00pm

Location: 

306 Rowland Hall

The classification of ancient solutions of CSF under some geometric conditions is a parabolic version of Liouville-type theorem. We will present that any ancient smooth embedded finite-entropy curve shortening flow is one of the following: a static line, a shrinking circle, a paper clip, a translating grim reaper, or a graphical ancient trombone constructed by Angenent-You. In particular, our result implies that any compact ancient smooth embedded finite-entropy flow is convex. Moreover, any non-compact ancient smooth embedded finite-entropy flow is either a static line or a complete graph over a fixed open interval. This is based on the joint work with Kyeongsu Choi, Dong-Hwi Seo, and Wei-Bo Su.

Enumerative problems for minimal surfaces with prescribed genus

Speaker: 

Adrian Chun-Pong Chu

Institution: 

Cornell University

Time: 

Tuesday, March 31, 2026 - 4:00pm to 5:00pm

Host: 

Location: 

306 Rowland Hall

We will present the enumerative min-max theory, which relates the number of genus g minimal surfaces in 3-manifolds to topological properties of the set of all embedded surfaces of genus ≤g. As a consequence, we can show that in every 3-sphere of positive Ricci curvature, there exist ≥5 minimal tori (confirming a conjecture by B. White (1989) in the Ricci-positive case), ≥4 minimal surfaces of genus 2, and ≥1 minimal surface of genus g for all g. This is based on a joint work with Yangyang Li and Zhihan Wang.

RTG Distinguished Lecture Talk 2: Invitation to Geometry via Mahler's Conjectures: a mathematical opera in three acts

Speaker: 

Yanir Rubinstein

Institution: 

Maryland and Stanford

Time: 

Tuesday, April 14, 2026 - 4:00pm to 5:00pm

Host: 

Location: 

RH306

Act I: Convexity, Duality, and Volume
Act II: Convex meets Differential
Act III: Convex meets Complex
Once convexity, duality and volume appear on stage, the Mahler
Conjectures are inevitable. These conjectures, originating in Number Theory,
predict the extremizers of the volume of a convex body times the volume of its dual.
They date from the 1930's and are still largely open. This "mathematical opera"
mostly aimed at a broad mathematical audience will attempt to recount the
over-a-century-old story of these beautiful conjectures, and their profound impact
on modern Geometric and Functional Analysis.

Feynman graph integral on Kahler manifolds

Speaker: 

Junrong Yan

Institution: 

Northeastern University

Time: 

Tuesday, February 10, 2026 - 4:00pm to 5:00pm

Host: 

Location: 

306 Rowland Hall

This is joint work with Minghao Wang. In this talk, I will explain the convergence of Feynman graph integrals on closed real-analytic K\"ahler manifolds: Using Getzler’s rescaling technique, the graph integrands extend naturally to the Fulton–MacPherson compactification as forms with divisorial singularities, allowing a rigorous definition as Cauchy principal value integrals. As an application, this yields a mathematical construction of the higher-genus B-model invariants on Calabi–Yau threefolds in the sense of Bershadsky–Cecotti–Ooguri–Vafa (BCOV).

Concavity Properties of Dirichlet Eigenfunctions in Hyperbolic Space

Speaker: 

Malik Tuerkoen

Institution: 

UC Irvine

Time: 

Tuesday, February 24, 2026 - 4:00pm to 5:00pm

Host: 

Location: 

306 Rowland Hall

On convex domains in R^n and S^n, the first Dirichlet eigenfunction is known to be log concave, a fact that is crucial to estimate the spectral gap, which is the difference between the second and first Dirichlet eigenvalue. It is known that the first Dirichlet eigenfunction is in general not log-concave for convex domains in H^n. I will discuss concavity estimates on horoconvex domains in hyperbolic space - which are domains whose boundaries second fundamental form is greater than 1 -  which yield new spectral-gap bounds in H^n. In doing so, we resolve a conjecture by Nguyen, Stancu and Wei. This is based on joint work with G. Khan and on joint work with S. Saha and G. Khan.

Some recent progress on the fully nonlinear Yamabe problem

Speaker: 

Baozhi Chu

Institution: 

UCSD

Time: 

Tuesday, January 13, 2026 - 3:00pm to 4:00pm

Location: 

RH 306

Abstract: The classical Yamabe problem—solved through the work of Yamabe, Trudinger, Aubin, and Schoen—asserts that on any closed smooth connected Riemannian manifold $(M^n,g)$, $n\geq 3$, one can find a metric conformal to $g$ with constant scalar curvature. A fully nonlinear analogue replaces the scalar curvature by symmetric functions of the Schouten tensor. Traditionally, the existing theory has required the scalar curvature to have a fixed sign. In a recent work, we broaden the scope of fully nonlinear Yamabe problem by establishing optimal Liouville-type theorems, local gradient estimates, and new existence and compactness results. Our results allow conformal metrics with scalar curvature of varying signs. A crucial new ingredient in our proofs is our enhanced understanding of solution behavior near isolated singularities. I will also discuss extensions to manifolds with boundary, treating prescribed boundary mean curvature and the boundary curvature arising from the Chern–Gauss–Bonnet formula.

 

Joint with Analysis seminar at 3pm.

 

 

Cohomology of Kaehler manifolds

Speaker: 

Matthias Wink

Institution: 

UCSB

Time: 

Tuesday, March 3, 2026 - 4:00pm

Host: 

Location: 

306 Rowland Hall

A celebrated result of Sui-Yau says that manifolds with positive bisectional curvature are biholomorphic to complex projective space. In this talk we will introduce new curvature conditions that provide characterizations of cohomology complex projective spaces. For example, the curvature tensor of a Kaehler manifold induces an operator on symmetric holomorphic 2-tensors, called Calabi operator. This operator is the identity for complex projective space with the Fubini Study metric. We show that a compact n-dimensional Kaehler manifold with n/2-positive Calabi curvature operator has the rational cohomology of complex projective space. The complex quadric shows that this result is sharp if n is even. This talk is based on joint work with K. Broder, J. Nienhaus, P. Petersen, J. Stanfield.

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