Mini-Workshop in Algebraic Geometry

Time：2019年7月9日

Room：管理科研楼1308室

**Schedule：**

09**:**00-10**:**00

Title：Rationality of Multi-variable Poincare Series

Speaker：Xi Chen (Universityof Alberta)

Abstract：Zariski conjectured that the Poincare seriesof a divisor on a smooth projective surface is rational. This was proved by Cutkosky and Srinivas in 1993. We areconsidering a generalization of this statement to multi-variable Poincare series. This is a joint work with J.Elizondo.

*Tea Break*

10**:**30-11**:**30

Title：Moduli of symmetric cubic fourfolds and nodal sextic curves

Speaker：Chenglong Yu (University of Pennsylvania)

Abstract：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.

*Lunch*

13**:**30-14**:**30

Title：The L2 representation of intersection cohomology

Speaker：Junchao Shentu (University of Science&Technology of China)

Abstract：The intersection cohomology is introduced by Goresky MacPherson as a cohomology theory on singular spaces (e.g. algebraic varieties) that satisfies the Poincare duality. After series of works by Goresky-MacPherson, Steenbrink, Beilinson- Bernstein- Deligne-Gabber, M. Saito and Cataldo-Migliorini, the whole (absolute and relative) Hodge-Lefschetz theorems are established. This makes intersection cohomology the most natural cohomology theory which is pure in the sense of Hodge theory. In this talk I will explain how to use differential forms to represent the intersection complex on an algebraic variety, at least when the variety admits only equi-singularities. This is an ongoing project, joint with Chen Zhao, willing to fill the analytic part (the de Rham Theorem) of the Hodge theory of the intersection cohomology.

14**:**40-15**:**40

Title：Cone spherical metrics, 1-forms andstable vector bundles on Riemann surfaces

Speaker：Jijian Song (Center for Applied Mathematics, TianjinUniversity)

Abstract：A cone spherical metric on acompact Riemann surface X is a conformal metric of constant curvature +1 withfinitely many conical singularities. The singularities of the metric can bedescribed by a real divisor D. An open question called Picard-Poincar′e problemis whether there exists a cone spherical metric for properly given (X; D) suchthat the singularities of the metric are described by the divisor D. In thistalk, I will report an existence result of meromorphic 1-forms with realperiods on Riemann surface and an angle constraint for reducible metrics on theRiemann sphere. For the irreducible metrics, by using projective structures, weprove that if D is effective, then they always can be obtained from rank 2stable vector bundles with line subbundles. At last, I will talk about how toconstruct a special class of cone spherical metrics by Strebel differentials.This is a joint work with Yiran Cheng, Bo Li, Lingguang Li and Bin Xu.

*Tea Break*

16**:**00-17**:**00

Title：Lyubeznik numbers ofirreducible projective varieties

Speaker：Botong Wang (University of Wisconsin-Madison)

Abstract：Lyubeznik numbers areinvariants of singularities that are defined algebraically, but has topologicalinterpretations. In positive characteristics, it is a theorem of Wenliang Zhangthat the Lyubeznik numbers of the cone of a projective variety do not depend onthe choice of the projective embedding. Recently, Thomas Reichelt, MorihikoSaito and Uli Walther related the problem with the failure of Hard Lefschetztheorem for singular varieties. And they constructed examples of reduciblecomplex projective varieties whose Lyubeznik numbers depend on the choice ofprojective embeddings. I will discuss their works and a generalization toirreducible projective varieties.

Organizers：Mao Sheng (University of Science andTechnology of China)

Sponsors：School of Mathematical Sciences, USTC