Seminars and Colloquia by Series

Geometric equations for matroid varieties

Series
Algebra Seminar
Time
Tuesday, September 21, 2021 - 10:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Ashley K. WheelerGeorgia Tech

Each point x in Gr(r,n) corresponds to an r×n matrix A_x which gives rise to a matroid M_x on its columns. Gel'fand, Goresky, MacPherson, and Serganova showed that the sets {y∈Gr(r,n)|M_y=M_x} form a stratification of Gr(r,n) with many beautiful properties. However, results of Mnëv and Sturmfels show that these strata can be quite complicated, and in particular may have arbitrary singularities. We study the ideals I_x of matroid varieties, the Zariski closures of these strata. We construct several classes of examples based on theorems from projective geometry and describe how the Grassmann-Cayley algebra may be used to derive non-trivial elements of I_x geometrically when the combinatorics of the matroid is sufficiently rich. 

(Differential) primary decomposition of modules

Series
Algebra Seminar
Time
Tuesday, September 14, 2021 - 10:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Justin ChenICERM/Georgia Tech

Primary decomposition is an indispensable tool in commutative algebra, both theoretically and computationally in practice. While primary decomposition of ideals is ubiquitous, the case for general modules is less well-known. I will give a comprehensive exposition of primary decomposition for modules, starting with a gentle review of practical symbolic algorithms, leading up to recent developments including differential primary decomposition and numerical primary decomposition. Based on joint works with Yairon Cid-Ruiz, Marc Harkonen, Robert Krone, and Anton Leykin.

Equivariant completions for degenerations of toric varieties

Series
Algebra Seminar
Time
Wednesday, March 24, 2021 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Netanel FriedenbergGeorgia Tech

After reviewing classical results about existence of completions of varieties, I will talk about a class of degenerations of toric varieties which have a combinatorial classification - normal toric varieties over rank one valuation rings. I will then discuss recent results about the existence of equivariant completions of such degenerations. In particular, I will show a result from my thesis about the existence of normal equivariant completions of these degenerations.

BlueJeans link: https://bluejeans.com/909590858?src=join_info

Equidistribution and Uniformity in Families of Curves

Series
Algebra Seminar
Time
Wednesday, March 17, 2021 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Lars KühneUniversity of Copenhagen

Please Note: This talk will be given via BlueJeans: https://bluejeans.com/531363037

In the talk, I will present an equidistribution result for families of (non-degenerate) subvarieties in a (general) family of abelian varieties. This extends a result of DeMarco and Mavraki for curves in fibered products of elliptic surfaces. Using this result, one can deduce a uniform version of the classical Bogomolov conjecture for curves embedded in their Jacobians, namely that the number of torsion points lying on them is uniformly bounded in the genus of the curve. This has been previously only known in few cases by work of David--Philippon and DeMarco--Krieger--Ye. Finally, one can obtain a rather uniform version of the Mordell-Lang conjecture as well by complementing a result of Dimitrov--Gao--Habegger: The number of rational points on a smooth algebraic curve defined over a number field can be bounded solely in terms of its genus and the Mordell-Weil rank of its Jacobian. Again, this was previously known only under additional assumptions (Stoll, Katz--Rabinoff--Zureick-Brown).

Tautological Bundles of Matroids

Series
Algebra Seminar
Time
Wednesday, March 3, 2021 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Chris EurStanford University

Matroid theory has seen fruitful developments arising from different algebro-geometric approaches, such as the K-theory of Grassmannians and Chow rings of wonderful compactifications. However, these developments have remained somewhat disjoint. We introduce "tautological bundles of matroids" as a new geometric framework for studying matroids. We show that it unifies, recovers, and extends much of these recent developments including log-concavity statements, as well as answering some open conjectures. This is an on-going work with Andrew Berget, Hunter Spink, and Dennis Tseng.

BlueJeans link: https://bluejeans.com/569437095

Uniform Asymptotic Growth of Symbolic Powers of Ideals

Series
Algebra Seminar
Time
Wednesday, February 24, 2021 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Robert WalkerUniversity of Wisconsin-Madison

Algebraic geometry (AG) is a major generalization of linear algebra which is fairly influential in mathematics. Since the 1980's with the development of computer algebra systems like Mathematica, AG has been leveraged in areas of STEM as diverse as statistics, robotic kinematics, computer science/geometric modeling, and mirror symmetry. Part one of my talk will be a brief introduction to AG, to two notions of taking powers of ideals (regular vs symbolic) in Noetherian commutative rings, and to the ideal containment problem that I study in my thesis. Part two of my talk will focus on stating the main results of my thesis in a user-ready form, giving a "comical" example or two of how to use them. At the risk of sounding like Paul Rudd in Ant-Man, I hope this talk will be awesome.

BlueJeans link: https://bluejeans.com/851535338

Defining canonically best factorization theorems for the generating functions of special convolution type sums

Series
Algebra Seminar
Time
Wednesday, February 10, 2021 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Maxie Schmidt

We are motivated by invertible matrix based constructions for expressing the coefficients of ordinary generating functions of special convolution type sums. The sum types we consider typically arise in classical number theoretic applications such as in expressing the Dirichlet convolutions $f \ast 1$ for any arithmetic function $f$. The starting point for this perspective is to consider the so-termed Lambert series generating function (LGF) factorization theorems that have been published over the past few years in work by Merca, Mousavi and Schmidt (collectively). In the LGF case, we are able to connect functions and constructions like divisor sums from multiplicative number theory to standard functions in the more additive theory of partitions. A natural question is to ask how we can replicate this type of unique "best possible", or most expressive expansion relating the generating functions of more general classes of convolution sums? In the talk, we start by summarizing the published results and work on this topic, and then move on to exploring how to define the notion of a "canonically best" factorization theorem to characterize this type of sum in more generality.

BlueJeans link: https://bluejeans.com/936847924

Variations of canonical measures: Riemann surfaces, graphs and hybrid curves

Series
Algebra Seminar
Time
Wednesday, December 2, 2020 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Noema Nicolussi

In the last years, connections between graphs and Riemann surfaces have been
discovered on several different levels. In particular, graphs are closely related
to singular Riemann surfaces and the boundary in the Deligne–Mumford com-
pactification of moduli spaces. Moreover, in both settings there is a notion of a
canonical measure (the Arakelov–Bergman and Zhang measures) which reflects
crucial geometric information.
In this talk, we focus on the following question: what is the limit of the canon-
ical measures along a family of Riemann surfaces? Combining the canonical
measures on Riemann surfaces and metric graphs, we obtain a full description
and a new compactification of the moduli space of Riemann surfaces in terms
of hybrid curves.

Based on joint work with Omid Amini (École polytechnique).

BlueJeans link: https://bluejeans.com/476849994

Hodge theory for tropical varieties 2

Series
Algebra Seminar
Time
Wednesday, November 18, 2020 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Omid Amini

Please Note: Part 2 of 3-part series

The aim of these two talks is to give an overview of our work on tropical Hodge theory. We show that cohomology groups of smooth projective tropical varieties verify hard Lefschetz property and Hodge-Riemann relations. Providing a description of the Chow groups of matroids in terms of cohomology groups of specific smooth projective tropical varieties, these results can be regarded as a generalization of the work of Adiprasito-Huh-Katz to more general tropical varieties. We also prove that smooth projective tropical varieties verify the analogue in the tropical setting of the weight-monodromy conjecture, affirming a conjecture of Mikhalkin and Zharkov.

BlueJeans link: https://bluejeans.com/476849994

Hodge theory for tropical varieties 1

Series
Algebra Seminar
Time
Wednesday, November 11, 2020 - 15:30 for 1 hour (actually 50 minutes)
Location
ONLINE
Speaker
Matthieu Piquerez

Please Note: Part 1 of 3-part series

The aim of these two talks is to give an overview of our work on tropical Hodge theory. We show that cohomology groups of smooth projective tropical varieties verify hard Lefschetz property and Hodge-Riemann relations. Providing a description of the Chow groups of matroids in terms of cohomology groups of specific smooth projective tropical varieties, these results can be regarded as a generalization of the work of Adiprasito-Huh-Katz to more general tropical varieties. We also prove that smooth projective tropical varieties verify the analogue in the tropical setting of the weight-monodromy conjecture, affirming a conjecture of Mikhalkin and Zharkov.

BlueJeans link: https://bluejeans.com/476849994

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