Formulae of one-partition and two-partition Hodge integrals

Speaker: 

Melissa Liu

Institution: 

Columbia University

Time: 

Wednesday, March 14, 2007 - 3:00pm

Location: 

MSTB 254

Many Hodge integral identities, including the ELSV formula of Hurwitz numbers and the lambda_g conjecture, are various limits of the formula of one-partition Hodge integrals conjectured by Marino and Vafa. Local Gromov-Witten invariants in all degrees and all genera of any toric surfaces in a Calabi-Yau threefold are determined by the formula of two-partition Hodge integrals. I will describe proofs of the formulae of one-partition and two-partition Hodge integrals based on joint works with Kefeng Liu and Jian Zhou.

Geometric Langlands conjecture as a Fourier transform

Speaker: 

Dmytro Arinkin

Institution: 

Caltech

Time: 

Tuesday, March 6, 2007 - 2:00pm

Location: 

MSTB 254

The Langlands conjecture originated as a highly non-trivial generalization of the reciprocity laws in number theory. In my talk, I explain how after certain `geometrization', it becomes a statement about sets (`moduli spaces') of vector bundles on a Riemann surface. The result is a kind of Fourier transform relating sets of vector bundles and local systems on a Riemann surface.

This `geometric Langlands transform' can be used to motivate theorems and conjectures in such diverse areas of mathematics (and physics) as theory of Painleve equations, representation theory of loop groups, autoduality of Jacobians, and mirror symmetry. Some of the relations will be explained in the talk.

Horseshoes in Multidimensional Scaling

Speaker: 

Professor Sharad Goel

Institution: 

USC

Time: 

Tuesday, March 20, 2007 - 11:00am

Location: 

MSTB 254

Classical multidimensional scaling (MDS) is a method for visualizing high-dimensional point clouds by mapping to low-dimensional Euclidean space. This mapping is defined in terms of eigenfunctions of a matrix of interpoint proximities. I'll discuss MDS applied to a specific dataset: the 2005 United States House of Representatives roll call votes. In this case, MDS outputs 'horseshoes' that are characteristic of dimensionality reduction techniques. I'll show that in general, a latent ordering of the data gives rise to these patterns when one only has local information. That is, when only the interpoint distances for nearby points are known accurately. Our results provide insight into manifold learning in the special case where the manifold is a curve. This work is joint with Persi Diaconis and Susan Holmes.

Hamiltonian Stationary Shrinkers and Expanders for Lagrangian Mean Curvature Flows

Speaker: 

Yng-Ing Li

Institution: 

National Taiwan University

Time: 

Tuesday, April 17, 2007 - 3:00pm

Location: 

MSTB 254

In this talk, I will report a recent joint work with Mu-Tao Wang. We construct examples of shrinkers and expanders for Lagrangian mean curvature flows. These examples are Hamiltonian stationary and asymptotic to the union of two Hamiltonian stationary cones found by Schoen and Wolfson. The Schoen-Wolfson cones are obstructions to the existence problems of special Lagragians or Lagrangian minimal surfaces in the variational approach. It is known that these cone singularities cannot be resolved by any smooth Lagrangian submanifolds. The shrinkers and expanders that we found can be glued together to yield solutions of the Brakke motion-a weak formulation of the mean curvature flow, and thus provide a canonical way to resolve the union of two such cone singularities. Our theorem is analogus to the Feldman-Ilmanen-Knopf gluing construction for the K\"ahler-Ricci flows.

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