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Linear representations of algebras and groups, Lie theory, associative algebras, multilinear algebra.

69 votes
Accepted

Consequences of Geometric Langlands

OK, this is a very broad question so I'll be telegraphic. There is a sequence of increasingly detailed conjectures going by the name GL -- it's really a "program" (harmonic analysis of $\mathcal{D}$-m …
57 votes
Accepted

Double affine Hecke algebras and mainstream mathematics

Well the first thing to say is to look at the very enthusiastic and world-encompassing papers of Cherednik himself on DAHA as the center of the mathematical world (say his 1998 ICM). I'll mention a c …
33 votes

What is significant about the half-sum of positive roots?

From the point of view of geometry, the crucial fact about $\rho$ is that the corresponding line bundle on the flag manifold is (upt to a sign) a (the) square-root of the canonical bundle (top exteri …
David Ben-Zvi's user avatar
32 votes
Accepted

A precise statement of the categorical version of geometric Langlands conjecture

For context for Tom's answer, let me state the naive version of the conjecture, which has been around since around 1997 I think (due to Beilinson-Drinfeld). It calls for an equivalence of (dg) catego …
David Ben-Zvi's user avatar
28 votes
Accepted

What role does the "dual Coxeter number" play in Lie theory (and should it be called the "Ka...

The dual Coxeter number comes up naturally as a normalization factor for invariant bilinear forms on the Lie algebra: according to Kac's book which you quote, $2h^{\vee}$ is the ratio between the Kill …
David Ben-Zvi's user avatar
22 votes

Why the BGG category O?

It might be worth pointing out a different motivation for Category O, namely the theory of Harish Chandra (g,K) modules. These are algebraic models for continuous representations of real reductive gro …
David Ben-Zvi's user avatar
22 votes
Accepted

Why can't we take three loops?

To elaborate on Kevin's excellent answer, one can account for the current absence of "higher loop" representation theory using physics. Namely, all of the representation theoretic structures you menti …
David Ben-Zvi's user avatar
22 votes
Accepted

LMS Lectures on Geometric Langlands

The videos from the LMS lectures and all of the GRASP videos are now available again from the links you gave (for download, not streaming). Many apologies for their long hiatus offline and many thanks …
David Ben-Zvi's user avatar
20 votes
Accepted

Virasoro action on the elliptic cohomology

There is an extensive math literature on related constructions. The key word is "chiral de Rham complex", introduced by Malikov, Schechtman and Vaintrob here and further developed in many many papers, …
David Ben-Zvi's user avatar
15 votes
Accepted

Why is the dual of a torus the same as its fundamental group?

The two are naturally dual lattices. The fundamental group of a torus $T$ can be canonically identified with the group (known as the cocharacter lattice) of $\it homomorphisms$ from the circle group t …
David Ben-Zvi's user avatar
13 votes
Accepted

What are local spaces and what are they good for?

Local spaces:finite subschemes::Factorization spaces:finite subsets. A local space over X is a compatible collection of spaces over the Hilbert schemes of arbitrary numbers of points in X satisfying …
David Ben-Zvi's user avatar
12 votes

How should I think about the Grothendieck-Springer alteration?

For Question 1 I agree with dhy that Namikawa's work is the relevant place to start, and from there the booming field of symplectic representation theory, which from one perspective is all about gener …
David Ben-Zvi's user avatar
11 votes
Accepted

Is there a gerbe Beilinson-Bernstein Localization?

[Edited to reflect Reimundo's comment] The question addresses categorified versions of the Borel-Weil-Bott theorem (and more generally Beilinson-Bernstein localization), which states an equivalence b …
David Ben-Zvi's user avatar
11 votes
Accepted

Is there any way to generalize the Laplacian to finite groups?

One natural generalization is the center of the group algebra (i.e., algebra of class functions - so in the abelian case you consider, just the group algebra itself). In the continuous case there are …
David Ben-Zvi's user avatar
10 votes
Accepted

Is D-module on flag variety of Lie algebra a scheme?

The de Rham space of a scheme is essentially never a scheme or algebraic space (unless I guess you're Spec of an Artin ring, in which case you'll get a discrete set of points). In particular this appl …
David Ben-Zvi's user avatar

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