Algebraic Geometry Seminar Spring 2013

The seminar meets on Fridays at 2:25 pm in Van Vleck B219.

The schedule for the previous semester is here.

Spring 2013

date	speaker	title	host(s)
January 25	Anatoly Libgober (UIC)	Albanese varieties of cyclic covers of plane, abelian varieties of CM type and orbifold pencils	Laurentiu
February 1	Laurentiu Maxim (University of Wisconsin-Madison)	Intersection spaces, perverse sheaves and type IIB string theory	local
March 1	Alexander Polishchuk (University of Oregon)	Lefschetz theorems for dg-categories with applications to matrix factorizations	Dima
March 15	Xue Hang (Columbia)	On the height of a canonical point in the Jacobian of a genus four curve	Tonghai
April 19	Xavier Gomez-Mont (CIMAT, Guanajuato, Mexico)	TBA	Laurentiu
April 26	Jack Huizenga (University of Illinois-Chicago)	Effective divisors on the Hilbert scheme of points in the plane and interpolation for stable bundles	Melanie
May 10	Yu-jong Tzeng (Harvard University)	TBA	Melanie

Abstract

Anatoly Libgober

Albanese varieties of cyclic covers of plane, abelian varieties of CM type and orbifold pencils

I'll describe the relation between Alexander modules of plane algebraic curves and maps of their complements onto orbifolds. A key step is a description of the Albanese variety of cyclic covers of the plane in terms of abelian varieties of CM type.

Laurentiu Maxim

Intersection spaces, perverse sheaves and type IIB string theory

The method of intersection spaces associates rational Poincare complexes to singular stratified spaces. For a complex projective hypersurface with only isolated singularities, we show that the cohomology of the associated intersection space is the hypercohomology of a perverse sheaf, the intersection space complex, on the hypersurface. We will discuss properties of the intersection space complex, such as self-duality, its betti numbers and mixed Hodge structures on its hypercohomology groups. This is joint work with Banagl and Budur.

Alexander Polishchuk

Lefschetz theorems for dg-categories with applications to matrix factorizations

I will describe versions of Lefschetz type formulas in the context of dg-categories. I will consider the case of the dg-category of matrix factorizations of an isolated hypersurface singularity and will show explicit calculations of the ingredients of the Lefschetz formula in this case.

Xue Hang

On the height of a canonical point in the Jacobian of a genus four curve

In this talk, we construct a quadratic point in the Jacobian of a non-hyperelliptic curve of genus four over a global field. We then compute the Neron--Tate height of this point in terms of the self-intersection of the admissible dualizing sheaf and some canonically defined local invariants. We show that the height of this point satisfies the Northcott property. We also give some estimates of the local invariants that appear in the height computation. When the reduction of the curve is simple, we compute explicitly the local invariants.

Jack Huizenga

Effective divisors on the Hilbert scheme of points in the plane and interpolation for stable bundles

The Hilbert scheme of n points in the projective plane parameterizes zero-dimensional subschemes of length n. An interesting problem is to describe the birational geometry of this space, and give modular interpretations for its various birational models. A first step in this program is to determine the cone of effective divisors on the Hilbert scheme.

We show the sections of many stable vector bundles satisfy a natural interpolation condition, and that these bundles always give rise to the edge of the effective cone. To do this, we give a generalization of Gaeta’s theorem on the resolution of the ideal sheaf of a general collection of n points in the plane. This resolution has a natural interpretation in terms of Bridgeland stability, and we observe that general ideal sheaves are always destabilized by exceptional bundles.