On Biproducts and Extensions
Yevgenia Kashina, Yorck Sommerhaeuser
该研究刻画了4阶初等阿贝尔群上特定八维Yetter-Drinfel'd Hopf代数的Radford双积能表示为Hopf代数扩张的具体形式，丰富了Hopf代数扩张理论的相关结论。
我们描述了4阶初等阿贝尔群上的某些八维Yetter-Drinfel'd Hopf代数的Radford双积可被表示为Hopf代数扩张的方式。
We describe in which ways the Radford biproducts of certain eight-dimensional Yetter-Drinfel'd Hopf algebras over the elementary abelian group of order 4 can be written as extensions of Hopf algebras.
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Radford $[(m,k),m]$-biproduct Theorem for Generalized Hom-crossed Products
本文通过引入左 $(m,k)$-Hom-叉积并结合左 $m$-Hom-smash 余积，建立并刻画了 Radford $[(m,k),m]$-双积定理，为构造 Hom-Hopf 代数提供新途径。
We give explicit formulas for maps in a long exact sequence connecting bialgebra cohomology to Hochschild cohomology. We give a sufficient condition for the connecting homomorphism to be surjective. We apply these results to compute all bialgebra two-cocycles of certain Radford biproducts (bosonizations). These two-cocycles are precisely those associated to the finite dimensional pointed Hopf algebras in the recent classification of Andruskiewitsch and Schneider, in an interpretation of these Hopf algebras as graded bialgebra deformations of Radford biproducts.
This paper studies the duals of some finite dimensional pointed Hopf algebras, with abelian group of grouplikes, over an algebraically closed field of characteristic 0, which are either Radford biproducts or else nontrivial liftings of a biproduct.
Biproduct Quasi-Hopf Algebras of Rank 2
受Radford工作启发，研究任意拟Hopf代数上左Yetter-Drinfeld模辫子范畴中的2维Hopf代数，确定其定义的双积拟Hopf代数，构造得到新的偶数维基本拟Hopf代数类与张量范畴类。
In continuation of our recent work about smash product Hom-Hopf algebras in \cite{MLY}, we introduce Hom-Yetter-Drinfeld category $_H^H{\mathbb{YD}}$ via Radford biproduct Hom-Hopf algebra, and prove that the Hom-Yetter-Drinfeld modules can provide solutions of the Hom-Yang-Baxter equation and $_H^H{\mathbb{YD}}$ is a pre-braided tensor category, where $(H, \b, S)$ is a Hom-Hopf algebra. Furthermore, we obtain that $(A^{\natural}_{\diamond} H,\aø\b)$ is a Radford biproduct Hom-Hopf algebra if and only if $(A,\a)$ is a Hopf algebra in the category $_H^H{\mathbb{YD}}$. At last, some examples and…
We study some problems related to lazy 2-cocycles, such as: extension of (lazy) 2-cocycles to a Drinfeld double and to a Radford biproduct, Yetter-Drinfeld data obtained from lazy 2-cocycles, lifting of projective representations afforded by lazy 2-cocycles.
On Isomorphisms between Certain Yetter-Drinfel'd Hopf Algebras
本文确定了作者先前研究的两族Yetter-Drinfel'd Hopf代数及其Radford双积的同构分类。
In formulating a generalized framework to study certain noncommutative algebras naturally arising in representation theory, K. A. Brown asked if every finitely generated Hopf algebra satisfying a polynomial identity was finite over a normal commutative Hopf subalgebra. In this note we show that Radford's biproduct, applied to the enveloping algebra of the Lie superalgebra pl(1,1), provides a noetherian prime counterexample.
Let $p,q$ be prime numbers with $p^4<q$, and $k$ an algebraically closed field of characteristic 0. We show that semisimple Hopf algebras of dimension $p^2q^2$ can be constructed either from group algebras and their duals by means of extensions, or from Radford biproduct $R#kG$, where $kG$ is the group algebra of group $G$ of order $p^2$, $R$ is a semisimple Yetter-Drinfeld Hopf algebra in ${}^{kG}_{kG}\mathcal{YD}$ of dimension $q^2$. As an application, the special case that the structure of semisimple Hopf algebras of dimension $4q^2$ is given.
Let $q$ be a prime number, $k$ an algebraically closed field of characteristic 0, and $H$ a non-trivial semisimple Hopf algebra of dimension $2q^3$. This paper proves that $H$ can be constructed either from group algebras and their duals by means of extensions, or from Radford's biproduct $H\cong R#kG$, where $kG$ is the group algebra of $G$ of order 2, $R$ is a semisimple Yetter-Drinfeld Hopf algebra in ${}^{kG}_{kG}\mathcal{YD}$ of dimension $q^3$.
Let $A$ be a Hopf algebra over a field $K$ of characteristic 0 and suppose there is a coalgebra projection $π$ from $A$ to a sub-Hopf algebra $H$ that splits the inclusion. If the projection is $H$-bilinear, then $A$ is isomorphic to a biproduct $R #_ξH$ where $(R,ξ)$ is called a pre-bialgebra with cocycle in the category $_{H}^{H}\mathcal{YD}$. The cocycle $ξ$ maps $R \otimes R$ to $H$. Examples of this situation include the liftings of pointed Hopf algebras with abelian group of points $Γ$ as classified by Andruskiewitsch and Schneider [AS1]. One asks when such an $A$ can be twisted by a coc…
Let $H$ be a Hopf algebra over a field $K$ of characteristic $0$ and let $A$ be a bialgebra or Hopf algebra such that $H$ is isomorphic to a sub-Hopf algebra of $A$ and there is an $H$-bilinear coalgebra projection $π$ from $A$ to $H$ which splits the inclusion. Then $A \cong R \#_ξH$ where $R$ is the pre-bialgebra of coinvariants. In this paper we study the deformations of $A$ by an $H$-bilinear cocycle. If $γ$ is a cocycle for $A$, then $γ$ can be restricted to a cocycle $γ_R$ for $R$, and $A^γ\cong R^{γ_R} \#_{ξ_γ} H$. As examples, we consider liftings of $\mathcal{B}(V) \# K[Γ]$ where $Γ$ …
Double cross products with projections and relative Rota-Baxter operators on Hopf algebras
本文研究带投影的双交叉积，证明其等价于Hopf代数上的相对Rota-Baxter算子，并探讨其与辫子算子及Doi-Hopf模态射的联系。
We introduce a family of braided Hopf algebras that generalizes the rank 1 Hopf algebras introduced by Krop anad Radford and we study its cleft extensions
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本文研究任意权无穷小（双Hom-）双代数的表示理论，提出双积双代数，揭示其与Rota-Baxter、树状及pre-Lie双模的联系，并给出两类Gelfand-Dorfman定理。
On partial actions of Hopf-Ore extensions
本文研究 Hopf 代数部分作用向 Hopf-Ore 扩张的提升方法，并据此刻画秩一 Hopf 代数（含广义 Taft 与 Radford 代数）的部分作用。
The unified product was defined in \cite{am3} related to the restricted extending structure problem for Hopf algebras: a Hopf algebra $E$ factorizes through a Hopf subalgebra $A$ and a subcoalgebra $H$ such that $1\in H$ if and only if $E$ is isomorphic to a unified product $A \ltimes H$. Using the concept of normality of a morphism of coalgebras in the sense of Andruskiewitsch and Devoto we prove an equivalent description for the unified product from the point of view of split morphisms of Hopf algebras. A Hopf algebra $E$ is isomorphic to a unified product $A \ltimes H$ if and only if there …
On Braided Differential Calculi and Quantum G-structures
该研究在辫子幺正范畴发展微分演算理论，结合双积构造协变smash积微分演算，引入量子G-结构并以实例说明，为量子几何提供新理论框架。
On Hopf algebras of dimension $p^n$ in characteristic $p$
本文研究特征 $p$ 代数闭域上含大量群样元或高维本原 Hopf 子代数的 $p^n$ 维 Hopf 代数，刻画其结构，并应用于 $p^2$ 维分类、Radford 代数、Sweedler 上同调及点态扩张。
A deeper understanding of recent computations of the Brauer group of Hopf algebras is attained by explaining why a direct product decomposition for this group holds and describing the non-interpreted factor occurring in it. For a Hopf algebra $B$ in a braided monoidal category $\C$, and under certain assumptions on the braiding (fulfilled if $\C$ is symmetric), we construct a sequence for the Brauer group $\BM(\C;B)$ of $B$-module algebras, generalizing Beattie's one. It allows one to prove that $\BM(\C;B) \cong \Br(\C) \times \Gal(\C;B),$ where $\Br(\C)$ is the Brauer group of $\C$ and $\Gal(…
We study a Hopf algebra $H$, which is finitely generated and projective over a commutative ring $k$, as a $P$-Frobenius algebra. We define modular functions in this setting, and provide a complete proof of Radford's formula for the fourth power of the antipode, using Frobenius algebraic techniques. As further applications, we extend Etingof and Gelaki's result that a separable and coseparable Hopf algebra has antipode of order two, the result of Schneider that Hopf subalgebras are twisted Frobenius extensions, and show that the quantum double is always a Frobenius algebra.
Noncommutative differential geometry on crossed product algebras
本文通过结合结构Hopf代数上的双协变微积分与基代数上的微积分，为任意裂扩张对应的交叉积代数构造了协变微分结构，得到具有典范强联络的量子主丛，并建立了联络与联络1-形式的一一对应。
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