## HaoHua Deng : Mumford-Tate Groups and the Hodge locus of period maps

- Algebraic Geometry ( 276 Views )Mumford-Tate groups together with their associated Mumford-Tate domains, as their definitions, tell rich information about Hodge classes. While Abelian varieties with complex multiplication serve as (relatively simple) examples, the study on Mumford-Tate groups in general cases could be much more complicated. In this expository talk I will briefly summarize the literature in the view of algebraic geometry and representation theory. The relation between Mumford-Tate groups and the Hodge-generic properties of period maps will be emphasized. I will also talk about some recent applications, including part of the latest results on the distribution of Hodge locus worked out by Baldi-Klingler-Ullmo. The talk is supposed to be accessible for graduate students in algebraic geometry or related fields.

## Chenglong Yu : Moduli of symmetric cubic fourfolds and nodal sextic curves

- Algebraic Geometry ( 222 Views )Period map is a powerful tool to study geometric objects related to K3 surfaces and cubic 4-folds. In this talk, we focus on moduli of cubic 4-folds and sextic curves with specified symmetries and singularities. We identify the geometric (GIT) compactifications with the Hodge theoretic (Looijenga, mostly Baily-Borel) compactifications of locally symmetric varieties. As a corollary, the algebra of GIT invariants is identified with the algebra of automorphic forms on the corresponding period domains. One of the key inputs is the functorial property of semi-toric compactifications of locally symmetric varieties. Our work generalizes results of Matsumoto-Sasaki-Yoshida, Allcock-Carlson-Toledo, Looijenga-Swierstra and Laza-Pearlstein-Zhang. This is joint work with Zhiwei Zheng.

## Ben Howard : Twisted Gross-Zagier theorems and central derivatives in Hida families

- Algebraic Geometry ( 177 Views )Abstract: Given a Hida family of modular forms, a conjecture of Greenberg predicts that L-functions of forms in the family should generically vanish to order 0 or 1 at the center of the functional equation. Similarly the Selmer groups of forms in the family should generically be of rank 0 or 1. In this talk I will prove a generalization of the Gross-Zagier theorem, relating Neron-Tate heights of special points on the modular Jacobian J_1(N) to derivatives of L-functions, and explain how this generalization can be used to verify Greenberg's conjecture for any particular Hida family.

## Thomas Lam : First steps in affine Schubert calculus

- Algebraic Geometry ( 156 Views )I will explain some attempts to develop a theory of Schubert calculus on the affine Grassmannian. I will begin with the different descriptions of the (co)homology rings due to Bott, Kostant and Kumar, and Ginzburg. Then I will discuss the problems of finding polynomial representatives for Schubert classes and the explicit determination of structure constants in (co)homology.

## Jie Wang : The primitive cohomology of the theta divisor of an abelian fivefold

- Algebraic Geometry ( 127 Views )The primitive cohomology of the theta divisor of a principally polarized abelian variety of dimension $g$ is a Hodge structure of level $g-3$. The Hodge conjecture predicts that it is contained in the image, under the Abel-Jacobi map, of the cohomology of a family of curves in the theta divisor. In this talk, I will explain how one can use the Prym map to show that this version of the Hodge conjecture is true for the theta divisor of a general abelian fivefold. This is joint work with Izadi and Tam\'as.

## Speaker unknown : On the converse theorem in the theory of Borcherds products

- Algebraic Geometry ( 32 Views )R. Borcherds constructed a lifting from elliptic modular forms of weight $1-n/2$ to meromorphic modular forms on the orthogonal group $O(2,n)$. The lifted modular forms can be written as infinite products analogous to the Dedekind $\eta$-function (``Borcherds products''). Moreover, their divisors are always linear combinations of Heegner divisors; these are algebraic divisors that come from embedded quotients of $O(2,n-1)$. We address the natural question, whether every meromorphic modular form on $O(2,n)$, whose divisor is a linear combination of Heegner divisors, is a Borcherds product? We discuss some recent results that answer this question in the affirmative in a large class of cases.