Algebra and Algebraic Geometry Seminar Spring 2023

The seminar normally meets 2:30-3:30pm on Fridays, in the room VV B223.

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Spring 2023 Schedule

date	speaker	title	host/link to talk
February 3	Dima Arinkin	Intergrating symplectic stacks	Local
February 24	Ruijie Yang	TBA	Maxim
March 10	Joerg Schuermann	TBA	Maxim
March 24	Daniel Corey	Degenerations of flag varieties and subdivisions of generalized permutahedra	Rodriguez
April 21	Christopher O'Neill	Numerical semigroups, minimal presentations, and posets	Sobieska

Abstracts

Dima Arinkin

Integrating symplectic stacks

Shifted symplectic stacks, introduced by Pantev, Toën, Vaquie, and Vezzosi, are a natural generalization of symplectic manifolds in derived algebraic geometry. The word `shifted' here refers to cohomological shift, which can naturally occur in the derived setting: after all, the tangent space is now not a vector space, but a complex. Several classes of interesting moduli stacks carry shifted simplectic structures.

In my talk (based on a joint project with T.Pantev and B.Toën), I will present a way to generate shifted symplectic stacks. Informally, it involves integration along a (compact oriented) topological manifold X: starting with a family of shifted symplectic stacks over X, we produce a new stack of sections of this family, and equip it with a symplectic structure via an appropriate version of the Poincaré duality.

Daniel Corey

Degenerations of flag varieties and subdivisions of generalized permutahedra

We study the initial degenerations of the type-A flag varieties, and show how they are related to flag matroid strata and subdivisions of flag matroid polytopes. As applications, we give a complete proof of a conjecture of Keel and Tevelev on log canonical compactifications of moduli spaces of hyperplanes in projective space in general position, and study the Chow quotient of the complete flag variety by the diagonal torus of the projective linear group. This is based on joint work with Olarte and Luber.

Christopher O'Neill

Numerical semigroups, minimal presentations, and posets

A numerical semigroup is a subset S of the natural numbers that is closed under addition.  One of the primary attributes of interest in commutative algebra are the relations (or trades) between the generators of S; any particular choice of minimal trades is called a minimal presentation of S (this is equivalent to choosing a minimal binomial generating set for the defining toric ideal of S).  In this talk, we present a method of constructing a minimal presentation of S from a portion of its divisibility poset. Time permitting, we will explore connections to polyhedral geometry.  

No familiarity with numerical semigroups or toric ideals will be assumed for this talk.