Algebra and Algebraic Geometry Seminar Fall 2023

The seminar normally meets 2:30-3:30pm on Fridays, in the room VV B135.

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Fall 2023 Schedule

date	speaker	title	host/link to talk
September 15	Joshua Mundinger	Quantization in positive characteristic	local
September 22	Andrei Negut	Computing K-HA's of quivers	local
October 6	Daniel Bragg (Utah)	A Stacky Murphy’s Law for the Stack of Curves	Josh
October 13	Xinchun Ma (UChicago)	TBA	Josh
November 3	Junyan Zhao	Moduli of curves and K-stability	Peter W
November 17	Purnaprajna Bangere	Syzygies of adjoint linear series on projective varieties	Michael K
December 1	Ekaterina Bogdanova (Harvard)	TBA	Dima

Abstracts

Joshua Mundinger

Quantization in positive characteristic

In order to answer basic questions in modular and geometric representation theory, Bezrukavnikov and Kaledin introduced quantizations of symplectic varieties in positive characteristic. These are certain noncommutative algebras over a field of positive characteristic which have a large center. I will discuss recent work describing how to construct an important class of modules over such algebras.

Andrei Negut

Computing K-HA's of quivers

Many interesting moduli stacks M in geometric representation theory admit interesting K-theoretic Hall algebras (K-HAs), defined by endowing the algebraic K-theory of M with an appropriate convolution product. While these algebras are notoriously hard to compute, they have an interesting relative called the shuffle algebra S. When M is a moduli stack of quiver representations, S is given by a collection of ideals inside polynomial rings, and their study can be reduced to commutative algebra. Fortunately/unfortunately, the commutative algebra in question is challenging, and we do not yet know of a complete description for a general quiver. In this talk, I will explain the general framework behind this problem, and survey results for the following special cases of quivers:

• double quivers arising in the theory of Nakajima quiver varieties
• quivers corresponding to symmetric Cartan matrices, yielding simply laced quantum loop groups
• quivers associated to toric Calabi-Yau threefolds in mathematical physics

Daniel Bragg

A Stacky Murphy’s Law for the Stack of Curves

Abstract: We show that every Deligne-Mumford gerbe over a field occurs as the residual gerbe of a point of the moduli stack of curves. Informally, this means that the moduli space of curves fails to be a fine moduli space in every possible way. We also show the same result for a list of other natural moduli problems. This is joint work with Max Lieblich.

Junyan Zhao

Moduli of curves and K-stability

The K-moduli theory provides us with an approach to study moduli of curves. In this talk, I will introduce the K-moduli of certain log Fano pairs and how it relates to moduli of curves. We will see that the K-moduli spaces interpolate between different compactifications of moduli of curves. In particular, the K-moduli gives the last several Hassett-Keel models of moduli of curves of genus six.

Purnaprajna Bangere

Syzygies of adjoint linear series on projective varieties

Syzygies of algebraic varieties have long been a topic of intense interest among algebraists and geometers alike. After the pioneering work of Mark Green on curves, numerous attempts have been made to extend some of these results to higher dimensions. It has been proposed that the syzygies of adjoint linear series L=K+mA, with A ample is a natural analogue for higher dimensions to explore. The very ampleness of adjoint linear series is not known for even threefolds. So the question that has been open for many years is the following (Question): If A is base point free and ample, does L satisfy property N_p for m>=n+1+p? Ein and Lazarsfeld proved this when A is very ample in 1991. In a joint work with Justin Lacini, we give a positive answer to the original question above.