# Algebraic Geometry/Commutative Algebra Seminar, 2017–2018

To volunteer to give a talk, or for anything else regarding the seminar, contact Claudiu Raicu.

Abstracts can be found below.

## Fall Schedule

The seminar will meet on Wednesdays, 3:00–4:00pm in 258 Hurley unless otherwise noted. Related events are also listed below.

Date Speaker Title
Wednesday, Aug. 30 Liubomir Chiriac (University of Massachusetts Amherst) Distribution of the Fourier coefficients in pairs of newforms
Wednesday, Sep. 6 Daniele Rosso (Indiana University Northwest) Irreducible components of exotic Springer fibers
Wednesday, Sep. 13 No seminar
Wednesday, Sep. 20 No seminar
Wednesday, Sep. 27 Mike Perlman (Notre Dame) Regularity of Pfaffian Thickenings
Wednesday, Oct. 4 Michael Wibmer (University of Pennsylvania) Free differential Galois groups
Wednesday, Oct. 11, 4-5pm
129 Hayes-Healy Hall
Department Colloquium
Anurag Singh (University of Utah) The number of equations defining an algebraic set
Thursday, Oct. 12, 2:30-3:30pm
Anurag Singh (University of Utah) Hankel determinantal rings
Wednesday, Oct. 18 No seminar (Fall break)
Wednesday, Oct. 25 Robin Hartshorne (U.C. Berkeley) Grothendieck duality
Wednesday, Nov. 1 Carl Wang-Erickson (Imperial College) Massey products in cohomology and a number-theoretic application
Wednesday, Nov. 8 Charles Doran (University of Alberta / ICERM) Calabi-Yau Manifolds, Mirrors, and Moduli
Thursday, Nov. 9
Department Colloquium
Markus Hunziker (Baylor University) Classical invariant theory and Harish-Chandra modules
Wednesday, Nov. 15 Nick Switala (UIC) The injective dimension of F-finite F-modules and holonomic D-modules
Wednesday, Nov. 22 No seminar (Thanksgiving)
Wednesday, Nov. 29 Tommy Kucera (University of Manitoba) The elementary socle series: Problems and Questions
Abstract
Wednesday, Dec. 6 Alex Constantinescu (University of Genova) TBA

## Abstracts

### Aug. 30, 2017

Speaker
Liubomir Chiriac (University of Massachusetts Amherst)
Title
Distribution of the Fourier coefficients in pairs of newforms
Abstract
Given two distinct newforms, I will present several statistical results concerning the joint distribution of their Fourier coefficients, with special emphasis on questions about dominance. The talk will touch upon refined multiplicity one problems in a few different contexts, as well as some applications of a natural generalization of the Sato-Tate conjecture for pairs of newforms.

### Sept. 6, 2017

Speaker
Daniele Rosso (Indiana University Northwest)
Title
Irreducible components of exotic Springer fibers
Abstract
The Springer resolution is a resolution of singularities of the variety of nilpotent elements in a reductive Lie algebra. It is an important geometric construction in representation theory, but some of its features are not as nice if we are working in Type C (Symplectic group). To make the symplectic case look more like the Type A case, Kato introduced the exotic nilpotent cone and its resolution, whose fibers are called the exotic Springer fibers. We give a combinatorial description of the irreducible components of these fibers in terms of standard Young bitableaux and obtain an exotic Robinson-Schensted correspondence. This is joint work with Vinoth Nandakumar and Neil Saunders.

### Sept. 27, 2017

Speaker
Mike Perlman (Notre Dame)
Title
Regularity of Pfaffian Thickenings
Abstract
Let $S$ be the coordinate ring on the spaces of $n\times n$ complex skew-symmetric matrices. This ring has a natural action of the general linear group $\textnormal{GL}_n(\mathbb{C})$, and we study the Castelnuovo-Mumford regularity of ideals $I\subseteq S$ that are invariant under this action. In particular, we compute the regularity of basic invariant ideals and large powers of ideals of Pfaffians. As a consequence, we characterize when these ideals have linear minimal free resolution. This work is inspired by the recent results of Raicu, who solved the analogous problem in the case of generic $n\times m$ matrices with a $\textnormal{GL}_n(\mathbb{C})\times \textnormal{GL}_m(\mathbb{C})$-action.

### Oct. 11, 2017

Speaker
Anurag Singh (University of Utah)
Title
The number of equations defining an algebraic set
Abstract
Given an algebraic set, i.e., the solution set of a family of polynomial equations, what is the minimal number of polynomials needed to define this set? The question is surprisingly difficult, with a rich history. We will give a partial survey, and discuss results and questions coming from local cohomology theory.

### Oct. 12, 2017

Speaker
Anurag Singh (University of Utah)
Title
Hankel determinantal rings
Abstract
We will discuss various aspects of rings defined by minors of Hankel matrices of indeterminates, and sketch a proof that these have rational singularities. This is joint work with Aldo Conca, Maral Mostafazadehfard, and Matteo Varbaro.

### Oct. 25, 2017

Speaker
Robin Hartshorne (U.C. Berkeley)
Title
Grothendieck duality
Abstract
I will explain the general idea of Grothendieck’s duality for coherent sheaf cohomology, with emphasis on his vision of the functorial nature of the theorem.

### Nov. 1, 2017

Speaker
Carl Wang-Erickson (Imperial College)
Title
Massey products in cohomology and a number-theoretic application
Abstract
We will explain how an appropriate infinity-algebra structure on cohomology allows for an explicit presentation of a deformation problem. This expands on the better-known mantra that deformations and obstructions arise from first and second degree cohomology, respectively. Deformations of group representations will be featured, in preparation for an application. The application will be drawn from joint work with Preston Wake, where we answer a question of Barry Mazur about congruences between Eisenstein series and cusp forms in terms of Massey products in Galois cohomology.

### Nov. 8, 2017

Speaker
Charles Doran (University of Alberta/ICERM)
Title
Calabi-Yau Manifolds, Mirrors, and Moduli
Abstract
Calabi-Yau manifolds are of central importance in both algebraic and differential geometry, and have a range of key applications in quantum field theory and string theory. Nevertheless, in dimensions three and higher our knowledge of their construction and effective moduli has historically been tied to the ambient spaces in which they live. Hodge-theoretic considerations suggest that a more natural way to build Calabi-Yau manifolds is “from the inside out” via internal fibrations. We will discuss a first-ever classification of such Calabi-Yau threefolds and implications for the structure of their moduli spaces. Furthermore, by identifying mirror partners, we are led to a new mirror symmetry conjecture which unifies the Calabi-Yau and Fano/Landau-Ginzburg mirror proposals (and answers a question of A. Tyurin).

### Nov. 9, 2017

Speaker
Markus Hunziker (Baylor University)
Title
Classical invariant theory and Harish-Chandra modules
Abstract
Classical invariant theory has played a central role in the development of modern mathematics and continues to have important applications in numerous areas of current interest. In this expository talk, I will present a new approach to classical invariant theory via combinatorics and representation theory related to Hermitian symmetric spaces. I will then explain how this approach can be used to solve several long-standing problems in invariant theory and beyond.

### Nov. 15, 2017

Speaker
Nick Switala (UIC)
Title
The injective dimension of F-finite F-modules and holonomic D-modules
Abstract
If M is an F-module over a regular Noetherian ring of positive characteristic, or a D-module over a formal power series ring with coefficients in a field of characteristic zero, Lyubeznik showed that the injective dimension of M is bounded above by the dimension of its support. If M is F-finite (respectively, holonomic), we show that the injective dimension of M is bounded below by one less than the dimension of its support, and therefore can take only two possible values. We do this by studying the last term in the minimal injective resolution of M. (This is joint work with Wenliang Zhang.)

Math Department - University of Notre Dame