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A Hopf algebra is a vector space $H$ over a field $k$ endowed with an associative product $\times:H\otimes_k H\to H$ and a coassociative coproduct $\Delta:H\to H\otimes_k H$ which is a morphism of algebras. Unit $1:k\to H$, counit $\epsilon:H\to k$ and antipode $S:H\to H$ are also required. Such a structure exists on the group algebra $k G$ of a finite group $G$.

9 votes
2 answers
1k views

Algebra in a category

I am try to understand the concept: an algebra in a category. Let $\mathcal{C}$ be a category and $A$ an object in $\mathcal{C}$. $A$ is an algebra in $\mathcal{C}$ means the multiplication $m: A \oti …
Jianrong Li's user avatar
  • 6,201
8 votes
1 answer
418 views

Compatibility conditions for Yetter-Drinfeld modules

In the paper, page 28, Definition 4.2.1, the compatibility condition for a Yetter-Drinfeld module over $H$ is $$ h_{(1)} v_{(-1)} \otimes h_{(2)}.v_{(0)} = (h_{(1)}.v)_{(-1)}h_{(2)} \otimes (h_{(1)}. …
Jianrong Li's user avatar
  • 6,201
7 votes
1 answer
181 views

How to translate multi-segments to Drinfeld polynomials?

Let $\hat{H}_m=\hat{H}_m(q)$ be the Iwahori-Hecke algebra of $GL_m$, see for example, Section 2. The simple $\hat{H}_m$-modules are parametrized by Zelevinsky's multi-segments, See Section 2.2 of the …
Jianrong Li's user avatar
  • 6,201
5 votes
1 answer
297 views

Center of quantum affine algebras

Are there some references about the center of quantum affine algebras? I searched on google and only find the paper. In particular, what is the center of $U_q(\widehat{\mathfrak{sl}_2})$. Thank you ve …
Jianrong Li's user avatar
  • 6,201
4 votes
1 answer
865 views

How to show that the graded dual of the universal enveloping algebra of a free Lie algebra o...

In the article, the universal enveloping algebra of a free Lie algebra on a set X is defined to be the free associative algebra generated by X. It is said that the graded dual of the universal envel …
Jianrong Li's user avatar
  • 6,201
4 votes
0 answers
301 views

Does the tensor algebra $T(V)$ of $V$ isomorphic to the symmetric algebra of the free Lie al...

Let $V$ be a finite dimensional vector space. Let $T(V)$ be the tensor algebra over $V$. Do we have $T(V) \cong S(Lie(V))$ as a graded vector space? Here $S(Lie(V))$ is the symmetric algebra of the …
Jianrong Li's user avatar
  • 6,201
3 votes
1 answer
123 views

Is $T(V) \rtimes T(V^* \otimes V)$ a bialgebra?

Let $V$ be a vector space and $V^*$ the dual vector space. Let $T(V)$ be the tensor algebra of $V$. The algebras $T(V)$ and $T(V^* \otimes V)$ are bialgebras. I am trying to find some bialgebra stru …
Jianrong Li's user avatar
  • 6,201
3 votes
1 answer
242 views

Are there p-adic or finite field analogue of Drinfeld-Jimbo's quantum groups

Drinfeld-Jimbo's quantum groups are associated algebras over the field of complex numbers. Are there some references about the analogue of Drinfeld-Jimbo's quantum groups over a p-adic field or a fini …
Jianrong Li's user avatar
  • 6,201
3 votes
1 answer
682 views

Deformation of a Hopf algebra

A deformation of a Hopf algebra is defined as follows. On page 171 of the book a guide to quantum groups, Remark 2, it is said that Any deformation of a Hopf algebra $A$ as a bialgebra is automatica …
Jianrong Li's user avatar
  • 6,201
3 votes
2 answers
243 views

How to show that Yetter-Drinfeld condition is equialent to $\Psi$ is a braiding

Let $H$ be a Hopf algebra and $V$ a right $H$-module and right $H$-comodule. The module $V$ is a Yetter-Drinfeld module over $H$ if and only if \begin{align} ( v \triangleleft h_{(2)} )_{(0)} \otimes …
Jianrong Li's user avatar
  • 6,201
2 votes
0 answers
310 views

Module algebras and comodule algebras

Let $H$ be a Hopf algebra and $A$ an algebra. Let $H^*$ be the dual Hopf algebra of $H$. Then by Proposition 1.6.11 in the book Foundations of Quantum Group Theory by Shahn Majid, $A$ is a right $H$-c …
Jianrong Li's user avatar
  • 6,201
2 votes
1 answer
179 views

Is the cross product $A \rtimes H$ a bialgebra?

Let $H$ be a bialgebra and $A$ a $H$-module algebra. The cross product $A \rtimes H$ is defined as follows. As a vector space $A \rtimes H = A \otimes H$. The multiplication on $A \rtimes H$ is define …
Jianrong Li's user avatar
  • 6,201
2 votes
1 answer
93 views

Are braided commutators primitive elements of a braided Hopf algebra?

Let $H$ be a braided Hopf algebra. The multiplication on $H \otimes H$ is defined by $(a \otimes b)(c \otimes d) = a \Psi(b \otimes c) d$, $a,b,c,d \in H$. Let $H = T(V)$. There is a algebra map $\D …
Jianrong Li's user avatar
  • 6,201
1 vote

How to translate multi-segments to Drinfeld polynomials?

This is described in equation (5.2) in the paper which follows from the paper: Quantum affine algebras and affine Hecke algebras.
Jianrong Li's user avatar
  • 6,201
1 vote
0 answers
127 views

References of an operator $T: V \otimes V \to V \otimes V$

Let $V$ be a vector space with a basis $v_1, \ldots, v_n$ and let $X_{ij} = v_i \otimes v_j$. Then $X_{ij}, i,j=1,\ldots, n$, is a basis of $V \otimes V$. Let $T: V \otimes V \to V \otimes V$ be the l …
Jianrong Li's user avatar
  • 6,201

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