Presentations

Noncommutative resolutions of Coulomb branches Monday, October 25, 2021

video of the talk  slides for the talk

Given a 3d N=4 supersymmetric quantum field theory, there is an associated Coulomb branch, which is an important reflection of the A-twist of this theory. In the case of gauge theories, this Coulomb branch has a description due to Braverman-Finkelberg-Nakajima; I'll discuss how we can generalize this geometric description in order to construct non-commutative resolutions of Coulomb branches (giving a more...

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Knot homology and coherent sheaves on Coulomb branches Thursday, April 8, 2021

video of the talk slides for the talk

Recent work of Aganagic proposes the construction of a homological knot invariant categorifying the Reshetikhin-Turaev invariants of miniscule representations of type ADE Lie algebras, using the geometry and physics of coherent sheaves on a space which one can alternately describe as a resolved slice in the affine Grassmannian, a space of G-monopoles with specified...

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Hypertoric mirror symmetry Thursday, November 5, 2020:

video of the talk

I’ve frequently heard the assertion that “hyperkahler manifolds are self-mirror up to rotation.” I’m not so sure this is true in general, but I know one example of such a variety:  multiplicative hypertoric varieties; these are what happens when you cut up a real torus into polytopes, and then send the polytopes to have a toric hyperkahler party.  I’ll discuss recent work with Gammage and McBreen showing that self-homological homological mirror symmetry after rotation...

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Coulomb branches and cylindrical KLRW algebras Friday, September 11, 2020:

video of the talk: part I

video of the talk: part II

Abstract:  Remarkable work of Braverman-Finkelberg-Nakajima has constructed, based on some fancy quantum field theory, a fascinating collection of spaces called "Coulomb branches." The definition of these involves the geometry of affine Grassmannians, and thus is not so easy for many people think about.  Luckily, the algebraic tools for understanding the most...

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Tensor functors and categorification Thursday, August 20, 2020:

video of the talk 

Abstract: One key tool in understanding categories of representations of Lie (super)algebras and quantum groups is how the fun tour of tensor product with finite dimensional representations behaves.  I’ll first explain how my work as well as that of many others has led to a good understanding of this in the type A case, and then say a few words about how we might generalize to BCD types.

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Howe to translate Gelfand-Tsetlin Wednesday, August 12, 2020

video of the talk  

Soergel bimodules have natural manifestations in 3 different contexts: combinatorial (i.e. diagrammatic calculus), geometric (i.e. perverse sheaves on the flag variety) and representation theoretic (i.e. Harish-Chandra bimodules/category O).  

In each of these contexts, there are generalizations that might interest you:

  • on the combinatorial side, there is a categorification of the kth tensor power of C^n via KLRW algebras, studied by Khovanov-Lauda-Sussan-Yonezawa...
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3d mirror symmetry and its discontents Monday, August 10, 2020

video of the talk

One of the central topics of the interaction between QFT and math is mirror symmetry for 2d theories. This theory has a more mysterious and exotic friend one dimension higher, sometimes called 3d mirror symmetry, which relates two 3-dimensional theories with N=4 supersymmetry. For roughly a decade, I struggled to understand this phenomenon without understanding what most of the words in the previous sentence meant. Eventually, I wised up and based on work of Braverman, Finkelberg, Nakajima, Dimofte,...

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S(ymplectic) duality: where do we stand?, at Fields Institute, Toronto, Friday, February 7, 2020

video of the talk

Around 2007, Braden, Licata, Proudfoot and I came up with the slightly daft idea that certain singular symplectic varieties come in dual pairs whose definition we could not explain, with relations between them that we struggled to articulate, let alone prove. By 2014, we were able to produce at least a coherent list of properties we expected to match in dual pairs, the most striking being a Koszul duality between associated category O's.

This was...

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Line defects and tilting bundles, at Fields Institute, University of Toronto, Tuesday, November 19, 2019:

video of the talk

Abstract: 

 

Work on Bezrukavnikov and Kaledin provides a bridge between representation theory and algebraic geometry, giving an equivalence of derived categories between certain categories of coherent sheaves and non-commutative algebras. Their original construction involved a strange detour into the land of characteristic p, but with some insight from 3-d gauge theory, we can avoid this in the case of BFN Coulomb branches,...

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