Events

The Four Flavours of Equivariant Derived Category and how They're Secretly the Same!

Speaker: Geoff Vooys

Abstract: There are (at least) four known approaches to the equivariant bounded derived category (EDC) known in the literature that people have used in various works. One is due to Bernstein-Lunts in the topological case and was extended rigorously to the scheme case by Pramod Achar.. A second approach to the EDC is the one presented by Lusztig in Cuspidal Local Systems and Graded Hecke Algebras II, which has the benefit of being intimately related to graded Hecke algebra. The third EDC we consider is the equivariant derived category of simplicial sheaves on the simplicial scheme approximating the quotient G \ X (cf., for instance, Deligne's Théorie de Hodge : III). Finally, the last EDC we consider is the one (essentially) defined by Kai Behrend in Derived $\ell$-adic Categories for Algebraic Stacks as a certain 2-colimit of constructible derived categories of $\ell$-adic sheaves on the quotient stack [G/X].
In this talk we will discuss not just what these objects are, but also sketch (emphasis on sketch here; there are a lot of ``no one wants to see this done live'' type details) how they can all be seen to be equivalent. In particular, I will discuss some notions of 2-coskeletal simplicial schemes that may be of interest to anyone interested in higher category theory or other areas of math that use simplicial techniques.

Zoom: 846139176

Event Date: 
Thursday, January 28, 2021 - 08:00 to 09:00
Project: 
Voganish

An ABV-packet for GL(16) with two representations

Speaker: Nicole Kitt
Abstract: It is known that not all ABV-packets are Arthur packets, and in particular, that Arthur packets for general linear groups are singletons. This talk concerns, what is believed to be, the smallest known example of an ABV-packet for a general linear group that is not a singleton, and hence is not of Arthur type. Specifically, we have shown that there is an irreducible admissible representation $\pi_{KS}$ of p-adic GL(16) with the property that its ABV-packet contains exactly one other irreducible representation, $\pi_{\psi}$.
The main tool that we use to calculate the ABV-packet for p-adic GL(16) is the functor Ev. In this talk, I will illustrate the geometric methods used to compute this functor. In particular, I will provide a sketch computation of the ABV-packet for GL(16). Before doing so, I will review ABV-packets and Vogan varieties for GL(n). This is joint work with Clifton Cunningham, based on prior joint work with Clifton and Reginald Lybbert; both of which included several enlightening conversations with Andrew Fiori.

Zoom link: 846139176

Event Date: 
Thursday, January 21, 2021 - 08:00 to 09:00
Project: 
Voganish

A-packets for quasisplit GSp(2n) and GSO(2n) over a p-adic field

Speaker: Bin Xu,

Arthur (1989) conjectured that the discrete spectrum of automorphic representations of a connected reductive group over a number field can be decomposed into global A-packets, in terms of which he also conjectured a multiplicity formula. Arthur (2013) proved his conjectures for symplectic and orthogonal groups, in which case the global A-packets are parametrized by self-dual automorphic representations of general linear groups. In this talk, I will give a construction of the local A-packets for general symplectic and general even orthogonal groups in the nonarchimedean case. This is based on our earlier works in the tempered case, and it follows a construction by Moeglin for symplectic and orthogonal groups.

Zoom: 846139176

Event Date: 
Thursday, September 24, 2020 - 08:30 to 10:00
Event Type: 
Project: 
Voganish

Quivers and their representations

Speaker: James Steele

Abstract: In this talk, we will give an introduction to quivers and their representations.

Talk on Zoom: 846139176.

Event Date: 
Thursday, September 17, 2020 - 08:30 to 09:30
Event Type: 
Project: 
Voganish

On SO(4) distinguished representations of G2

Speaker: Sarah Dijols,

Abstract: In this talk, we will report some recent progress on SO(4)-distinguished representations of G2. This is a joint work with Jerrod Smith.

Zoom Link: 846139176

Event Date: 
Thursday, August 20, 2020 - 08:30 to 09:30
Event Type: 

Distinguished Arthur parameters and relative discrete series

Speaker: Jerrod Smith,

Abstract: In this talk, we will report the recent progress on representations of GL(2n) distinguished by symplectic group Sp(2n) and those representations distinguished by unitary groups.

Reference: Jerrod Smith, Speh representations are relatively discrete, to appear in Representation Theory (2020).

Zoom Link: 846139176

Event Date: 
Thursday, July 30, 2020 - 08:30 to 09:30
Event Type: 
Notes: 

Voganish Seminar: Arthur packets of unipotent representations of G2

Speaker: Clifton Cunningham,

Abstract: In this talk, we will explain how to realize the theta correspondence geometrically in the case of G2, it’s relation to endoscopy, and a cool thing that happens when you include pure inner forms.

Zoom link: 846139176

Event Date: 
Wednesday, July 8, 2020 - 10:00 to 11:00
Event Type: 
Project: 
Voganish

Voganish Seminar: Geometric induction from PGL(3) to G2

Speaker: Andrew Fiori,

Abstract: In this talk, we will consider the geometric induction from perverse sheaves of PGL(3) to G_2 and then compare it with the endoscopic transfer from PGL(3) to G_2.

Zoom link: 846139176

Event Date: 
Wednesday, June 24, 2020 - 08:30 to 09:30
Event Type: 
Project: 
Voganish

Endoscopic transfer from PGL(3) to G_2

Speaker: Qing Zhang,

Abstract: In this talk, we will give an introduction of the unipotent representations of PGL_3 and its pure inner forms and the transfer of these representations, following work by Gan & Savin.

Talk via Zoom: 846139176

Event Date: 
Wednesday, June 17, 2020 - 08:30 to 09:30
Event Type: 
Project: 
Voganish

Arthur packets for G(2) and perverse sheaves on cubics

Speaker: Clifton Cunningham (University of Calgary)

Abstract: This talk demonstrates a non-invasive procedure that calculates Arthur packets, their associated stable distributions and Langlands-Shelstad transfers, without direct use of endoscopy, using certain unipotent representations of the split p-adic exceptional group G(2) as examples. In the case at hand, this procedure relies on a study of the category of GL(2)-equivariant perverse sheaves on the moduli space of homogeneous cubics in two variables, which is perhaps of independent interest. Specifically, we find the Fourier transform and the microlocalization of the simple objects in this category, and convert that into information about the Aubert involution and stable distributions attached to Arthur packets. This is joint work with Andrew Fiori and Qing Zhang, based on earlier joint work with Andrew Fiori, Ahmed Moussaoui, James Mracek and Bin Xu, which is based on earlier work by David Vogan, sadly, not joint.

This is one of Lie group seminar event of MIT, see https://researchseminars.org/seminar/MITLie

Event Date: 
Thursday, May 7, 2020 - 16:30 to 17:30

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