All Questions
Tagged with rt.representation-theory qa.quantum-algebra
149 questions
7
votes
1
answer
672
views
The Irreducible Corepresentations of the eight-dimensional Kac-Paljutkin Quantum Group
I asked this question on Math.Stack but have not had any answers.
Question
What are the irreducible corepresentations of the eight-dimensional Kac-Paljutkin Quantum Group, $A$?
The trivial ...
- 1,027
5
votes
1
answer
297
views
Quantum 9j symbols?
A formula for (SU2) quantum 6j symbols exists. A formula expressing ordinary (q=1)
9j symbols in terms of 6j symbols is long known. Unfortunately, combining both (I tried it myself) got tricky - the ...
- 4,829
1
vote
0
answers
216
views
polynomial representation of $sl_{2}(k)$
Let $k$ be an algebraic closed field of characteristic 0. We write
$$X=\left(
\begin{array}{ccc}
0 & 1\\
0 & 0\\
\end{array}
\right),~~
Y=\left(
\begin{array}{ccc}
0 & 0\\
1 & 0\\
\...
1
vote
1
answer
168
views
Decomposition of C' Kazhdan-Lusztig basis element associated to longest word in S_n
I'm trying to decompose the Kazhdan-Lusztig C' basis element associated to the longest word in $S_n$, $C'_{w_0}$ into products and sums of elements $C'_w$ where $w < w_0$ in the Bruhat order. For ...
- 115
3
votes
0
answers
323
views
Quantum Coordinate Algebras at Roots of Unity and Non-Standard Irrep Types
Let $\frak{g}$ be a complex semi-simple Lie algebra of rank $n$, and $U_q(\frak{g})$ the corresponding Drinfeld-Jimbo algebra. As is well-known, for $q$ not a root of unity, the irreducible finite-...
- 1,453
5
votes
4
answers
532
views
Non-Drinfeld–Jimbo deformations and finite quantum groups
As is well-known, for the compact semi-simple Lie groups $G$, there exist non-commutative Hopf algebra deformations ${\cal O}_q[G]$ of their coordinate algebras ${\cal O}[G]$, the so-called Drinfeld--...
- 263
2
votes
1
answer
228
views
A question on Lusztig's `graph with automorphism' construction?
Using the notion of a graph with compatible automorphism, Lusztig constructs all symmetrizable Cartan data (i.e. Cartan matrices $A$ for which there is a diagonal matrix $D=\mathrm{diag}(d_1,\ldots,...
- 1,472
8
votes
0
answers
488
views
det(A)det(B) = det(AB+correction), Capelli identities, "factorized" representation of $\mathfrak {gl}_n$
Context: Some probably know that there are Capelli identities which state
$$det(A)det(B) = det(AB+correction)$$ for some matrices with non-commuting elements, they go back to the 19-th century, but ...
- 24.9k
5
votes
2
answers
923
views
Status of a conjectural definition of H. Nakajima
In his paper '$t$-analogue of $q$-characters of finite dimensional representations of quantum affine algebras' - http://arxiv.org/abs/math/0009231 - H. Nakajima states a conjectural definition of the $...
- 1,201
0
votes
2
answers
203
views
Structure of Homomorphisms of commutative C^* algebra
Being new to $C$* algebra, I'm trying to understand basic properties of -homomorphisms of such algebras. Let $P$ be a set of commuting projections on Hilbert space ${\cal H}$.
Let ${\cal P}$ be the $...
- 45
4
votes
1
answer
629
views
Kazhdan Lusztig Map and conjugacy classes of Weyl groups.
The Kazhdan Lusztig map gives a correspondence between conjugacy classes of Weyl groups and nilpotent orbits. So, let $w$ be a conjugacy class and
$N$ be the nilpotent orbit it gets mapped to under ...
- 1,073
4
votes
0
answers
203
views
The Killing form on quantized enveloping algebras and reduction to the classical case
Let $U_q$ be the quantized enveloping algebra associated to a semisimple Lie algebra $\mathfrak g$. It is a result due to Tanisaki (see here; also see Chapter 6 of Jantzen's book Lectures on Quantum ...
- 3,637
4
votes
1
answer
280
views
Vertex embeddings of quantum groups via quivers
Let Uq be a quantised enveloping algebra of type affine ADE (untwisted). By the loop presentation of Uq, we see that for each vertex of the finite Dynkin diagram, there is an inclusion Uq($\hat{sl_2}$)...
- 8,866
6
votes
4
answers
2k
views
level 2,3 characters of affine su(2)
Does anyone know where I can find an explicit formula to compute the level 2 or level 3
characters of affine $su(2)$? I have found several sources that give a formula to compute the
level 1 ...
- 1,709
12
votes
1
answer
723
views
Unitary representations of Quantum Groups
Let $\mathfrak{g}$ be a finite-dimensional complex simple Lie algebra and let $U_q(\mathfrak{g})$ be some incarnation of the quantized universal enveloping algebra of $\mathfrak{g}$; here I am ...
- 8,559
16
votes
0
answers
824
views
Capelli determinant = Duflo ( determinant) - was it known ?
Question briefly. Was this fact known: Capelli determinant = Duflo (determinant) ? (This is an equality of the two central elements in universal enveloping of Lie algebra $gl_n$).
I googled a lot ...
- 24.9k
13
votes
2
answers
1k
views
Intrinsic characterization of Soergel bimodules?
A Soergel bimodule (for $S_n$) is a bimodule over $R = \mathbb{Q}[x_1,\dots,x_n]$ which appears as a summand/grading shift of tensor products of the basic bimodules
$$B_{i,i+1} = R \otimes_{i,i+1} R$$
...
- 10.1k
2
votes
4
answers
650
views
Role of fiber functor monoidal structure in Tannakian bialgebra reconstruction
Shahn Majid presents in section 9.4 of "Foundatations of Quantum Group Theory" a Tannaka-type reconstruction theorem for producing a $k$-bialgebra out of its $k$-linear monoidal category of modules $\...
- 1,368
6
votes
0
answers
238
views
Category of modules over a coPoisson-bialgebra
Fix a ground commutative ring $k$. A coPoisson-bialgebra is a bialgebra $H$ equipped with a linear mapping $\pi:H \rightarrow H \otimes_k H$ s.t.
$\pi$ is a coLie bracket
$\pi$ is a coderivation
$\pi(...
- 1,368
5
votes
1
answer
564
views
Is there a fusion rule in positive characteristic?
Verlinde's fusion gives a certain "tensor product" of representations of loop groups. The category of representations of loop groups has (essentially equivalent) two incarnations. One is analytic, ...
- 18.7k
1
vote
0
answers
121
views
Product knot invariants
Let $I_1(L)$ be a Reshetikhine-Turaev link invariant coming from the (quantum Lie) group $G_1$ and representation $\lambda_1$ having the S matrix $S_1$. Let $I_2(L)$ be a Reshetikhine-Turaev link ...
- 4,829
41
votes
3
answers
3k
views
Why is there such a close resemblance between the unitary representation theory of the Virasoro algebra and that of the Temperley-Lieb algebra?
For those who aren't familiar with the Virasoro or Temperley-Lieb algebras, I include some definitions:
• The (universal envelopping algebra of the) Virasoro algebra is the $\star$-algebra $...
- 43.2k
12
votes
0
answers
605
views
Given an algebra, can it be realized as a block of a Hopf algebra?
During a classification problem I came across a set of algebras given as the path algebra of a quiver with relations. As an example the local ones: $k\langle x,y\rangle/x^2,y^2, xy-qyx$, where $q\in k$...
- 2,450
5
votes
2
answers
384
views
a question about finite dimensional representation of a Hopf algebra
Let $H$ be a Hopf algebra over a field $k$ and $V$ a finite
dimensional left $H$-module. Then $End_{k}(V)$ is a right $H$-module
via $(f\cdot h)(v)=S(h_{1})f(h_{2}\cdot v)$.
We set $Ann(End_{k}(V))$={...
1
vote
0
answers
247
views
Annulator of Tensor Power in a Quantum Group
There is a little question haunted me for few days. I will be grateful to anyone who can give me any clue how to solve it.
Let $V$ be a nontrivial module of $\mathrm{U}_q(\mathfrak{g})$ (the ...
- 153
15
votes
1
answer
700
views
Why do sl(2) and so(3) correspond to different points on the Vogel plane?
Vogel assigns to every simple metric Lie algebra (and more generally to every simple metric Lie algebra object in a symmetric monoidal category) a point in the orbifold $\mathbb{P}^2/S_3$ (where $S_3$ ...
- 28.1k
7
votes
0
answers
400
views
Quantum Drinfeld-Sokolov reduction of a Whittaker module
Take a Whittaker module $Wh$ of a (finite or affine) semi-simple Lie algebra $\mathfrak{g}$ , and apply the quantum Drinfeld-Sokolov reduction $qDS$ with respect to an $sl(2)$ embedding $\rho:sl(2) \...
- 6,123
8
votes
0
answers
917
views
duality between universal enveloping and function algebra for GL(n)
Motivation. Few years ago I constructed a family of internal Hopf algebras in the Loday-Pirashvili tensor category of linear maps which is in a sense a generalization of the algebra of regular ...
- 5,232
3
votes
0
answers
515
views
What happens geometrically when you take associated-graded (or complete, ...) of a group ring at its augmentation ideal?
I am interested in the following functor from Monoids (in $\text{Set}$) to Graded Lie Algebras (over a fixed field of characteristic $0$). (By "graded" I mean only that my Lie algebras have some ...
- 54.6k
12
votes
3
answers
1k
views
Simple modules for $U_q(\mathfrak{sl}_n)$ at roots of unity
Can anyone point me to a classification/construction of the irreducibles for $U_q(\mathfrak{sl}_n)$, or the associated small quantum groups, when the parameter $q$ is a root of unity and $n>2$? ...
- 2,721
10
votes
2
answers
902
views
An explicit description of $\operatorname{gr}(k \cdot G)$ for the filtration induced by the augmentation ideal?
Let $A$ be any bialgebra (associative, unital, etc.) over a ring $k$. Then among other things it has a counit $\epsilon : A \to k$, and hence an augmentation ideal $I = \ker \epsilon$, which is a ...
- 54.6k
4
votes
0
answers
110
views
Is there a good reference for how ribbon structures change when one switches coproducts?
I'm just going assume readers are familiar with the notions of R-matrix and ribbon categories.
Given a quasi-triangular Hopf algebra $A$ with $R$-matrix $R$, one can construct the co-opposite Hopf ...
- 44.7k
6
votes
1
answer
634
views
What is the image of the half/full twist in the Hecke algebra, in the Kazhdan-Lusztig basis? What is the corresponding complex of Soergel bimodules?
Let $B_n$ be the braid group on $n$ strands. It has generators $\tau_i$ for $i = 1,\ldots,n-1$ which exchange the $i$th and $(i+1)$st strands, and which satisfy the relations
$\tau_i \tau_j = \tau_j \...
- 8,723
26
votes
2
answers
3k
views
When does Lusztig's canonical basis have non-positive structure coefficients?
I've heard asserted in talks quite a few times that Lusztig's canonical basis for irreducible representations is known to not always have positive structure coefficents for the action of $E_i$ and $...
- 44.7k
2
votes
1
answer
476
views
Are there other algebra structures on the regular representation of a group?
Let $G$ be a (discrete, say) group and $\mathbb K$ a field. The regular representation $G^{\mathbb K}$ is the vector space of all functions $G \to \mathbb K$. It is a (left, say) $G$-module: given $...
- 54.6k
4
votes
0
answers
241
views
Analogy between canonical basis of U(n_-) and Schur functors, each under restriction
.1. For any category $\mathcal C$, possibly enriched over schemes, define $Rep({\mathcal C})$ to be the functor category ${\mathcal C} \to {\bf Vec}$ with direct sum inherited from $\bf Vec$. (If $\...
- 27.8k
5
votes
3
answers
2k
views
Practical Ways to get Skew-Schur Functions
The Schur polynomials satisfy many, many identities and there is a whole book about them.
I think the easiest way is with the Vandermonde Determinant.
$$s_{3,1,1}(a,b,c) = \frac{\left|\begin{array}{...
- 22.8k
12
votes
1
answer
891
views
Do Jones-Wenzl idempotents lift to anything interesting in the Hecke algebra?
Background
Inside the Temperley-Lieb algebra $TL_n$ (with loop value $\delta=-[2]$ and standard generators $e_1,\ldots,e_{n-1}$), the Jones-Wenzl idempotent is the unique non-zero element $f^{(n)}$ ...
- 1,756
5
votes
3
answers
348
views
Software for Planar Algebras or Group Rings
Does software exists for calculating with planar algebras or group rings? It could be part of Mathematica or be an extension of Python or Java or C. What would go into designing such a data-type ...
- 22.8k
10
votes
1
answer
871
views
Is there a good reference for the relationship between the Yangian and formal based loop group?
For every finite dimensional semi-simple Lie group $\mathfrak{g}$, we have a loop algebra $\mathfrak{g}[t,t^{-1}]$. This loop algebra has a natural invariant inner product by taking the residue at ...
- 44.7k
12
votes
2
answers
2k
views
Is there a machinery describing all the irreducible representations ?
Suppose we have a finite dimensional Lie algebra $g$， Is there a machinery to describe all the irreducible representation of $g$.
Consider toy example: $sl_{2}$ or $sl_{3}$, how do we describe all ...
- 1,305
12
votes
1
answer
840
views
Comparing two similar procedures for quantizing a Casimir Lie algebra
My primary reference for this question is the very good book Quantum Groups and Knot Invariants by C. Kassel, M. Rosso, and V. Turaev. I'm also drawing from P. Etingof and O. Schiffmann, Lectures on ...
- 54.6k
5
votes
1
answer
951
views
Does the canonical basis of a tensor product of quantum group representations span the isotypic components of tilting modules?
It's a theorem of Lusztig that if one takes two (or more) representations of a quantum group at a non-root-of-unity choice of $q$, and look at the canonical basis of their tensor product, then each ...
- 44.7k
6
votes
1
answer
298
views
Are there elements of fixed weight in a crystal not killed by too many Kashiwara operators?
I've come across an annoying lemma trying to finish up an argument, and I was hoping one of you guys knew about it.
Question: Given
a weight $\lambda$ of a simple Lie algebra $\mathfrak g$, and
...
- 44.7k
8
votes
3
answers
1k
views
Is there an analogue Beilinson-Bernstein localization for quantized enveloping algebra
I am completely a beginner in this field. I wonder know whether there is appropriate notion for quantum flag variety of finite dimensional Lie algebra. If so, what is the correspondent notion for &...
- 81
7
votes
0
answers
213
views
Decomposition of certain projectives for cyclotomic q-Schur algebras
In representation theory, a very popular set of finite dimensional algebras are the $q$-Schur algebras, which are given by looking at the endomorphisms of $V^{\otimes d}$ where $V$ is the standard ...
- 44.7k
6
votes
2
answers
1k
views
Categorifications of the Fibonacci Fusion Ring arising from Conformal Field Theory
I was reading about realizations of the "Fibonacci" fusion ring $X \otimes X = X \oplus 1$ in Fusion Categories of Rank 2 by Victor Ostrik. Apparently, there are two of them and they arise in various ...
- 22.8k
8
votes
2
answers
819
views
Are there interesting monoidal structures on representations of quantum affine algebras?
Is there a good monoidal structure on a category of integrable representations of a quantum affine algebra? In the ordinary affine Kac-Moody case, there is the usual tensor product (symmetric, adds ...
- 45.7k
5
votes
1
answer
404
views
What is the "right" hermitian structure on tensor products of quantum group representations?
This is pretty specific, but there are some experts around.
So, in Chari & Pressley, it's explained that in the standard *-structure, every irreducible, finite-dimensional representation of a ...
- 44.7k