Hopf Galois扩张与Hopf模结构定理

设Ｈ是域ｋ上任意的Ｈｏｐｆ代数。本文首先讨论了右Ｈ＿扩张Ａ／Ａ￣（ｃｏＨ）与Ｈｏｐｆ模范畴，给出了Ａ／Ａ￣（ｃｏＨ）为右Ｈ－Ｇａｌｏｉｓ扩张的充分必要条件和Ｈｏｐｆ模范畴满足结构定理的若干等价条件．然后我们讨论了不可约作用与除环的Ｇａｌｏｉｓ扩张．     

A#H^＊rat为中心单代数的条件

本文用ＭｏｒｉｔａＣｏｎｔｅｘｔ的方法得到域上余ＦｒｏｂｅｎｉｕｓＨｏｐｆ代数Ｈ与Ｈ－余摸代数Ａ的Ｓｍａｓｈ积Ａ＃Ｈ＊ｒａｔ是中心单代数的条件：若Ａ／ＡＣｏＨ是Ｈ－Ｇａｌｏｉｓ扩张，且ＡＣｏＨ是中心单代数，则Ａ＃Ｈ＊ｒａｔ也是中心单代数，特别地，若ＡＣｏＨｋ，则Ａ＃Ｈ＊ｒａｔ是中心单代数，且为ｋ－空间Ａ上线性变换稠密环．作为推论给出Ｈ＃Ｈ＊ｒａｔ是本原中心单代数新的证明．     

环的Galois,分离和Frobenius扩张

设∧是其中心Ｃ＿∧上的有限维单代数，Ｆ是满足Ｃ＿∧的∧的子环，Ｇ是保持Γ的元素不变的∧的自同构的有限群．本文证明：若∧／Γ是Ｇ－Ｇａｌｏｉｓ扩张，则在∧中的中心化子△是Ｃ＿Γ一分离代数且∧／Γ是Ｆｒｏｂｅｎｉｕｓ扩张，这里Ｃ＿Γ是Γ的中心．     

除环的Hopf Galois扩张与Hopf模

设Ｈｏｐｆ代数Ｈ余作用于代数Ａ．本文讨论代数Ａ，余不变子代数ＡｃｏＨ及Ｓｍａｓｈ积Ａ＃Ｈ的相互关系．同时将研究Ｈｏｐｆ模，全积分及除环的ＨｏｐｆＧａｌｏｉｓ扩张．     

QF环性质向扩环上的传递

设环Ａ是环Ｂ的扩环（记作Ａ／Ｂ），Ｂ是ＱＦ环，在本文中我们将证明在以下四种情形下Ａ也是ＱＦ环：（１）_ＢＡ是有限生成自由的且Ａ／Ｂ是投射扩张．（２）Ａ／Ｂ是Ｆｒｏｂｅｎｉｕｓ的．（３）Ａ／Ｂ是可离且平坦的．（４）Ａ／Ｂ是Ｈ－可离的．     

关于交换环上带正则基的Hopf-Galois扩张的同构类

本文考虑交换环上带正则基的Ｈｏｐｆ－Ｇａｌｏｉｓ扩张的刻划及其同构类集合的结 构．主要结论是：当Ｂ为一交换环、Ｈ为余交换的有限Ｈｏｐｆ时,上述同构类集合 构成群并与 Ｌ~＊＝（ＢＨ）~＊的 ２次上同调群 Ｈ~２（Ｌ~＊, Ｕ）同构．     

关于交换环上带正则基的Hopf-Galois扩张的同构类

本文考虑交换环上带正则基的Ｈｏｐｆ－Ｇａｌｏｉｓ扩张的刻划及其同构类集合的结 构．主要结论是：当Ｂ为一交换环、Ｈ为余交换的有限Ｈｏｐｆ时,上述同构类集合 构成群并与 Ｌ~＊＝（ＢＨ）~＊的 ２次上同调群 Ｈ~２（Ｌ~＊, Ｕ）同构．     

关于余模代数的Hopf—Jacobson根的一些结果

设Ｈ是Ｈｏｐｆ代数，Ａ是右Ｈ－余模代数，若（，）满射，则Ｊ（Ａ＾ｃｏＨ）＝Ｌ＾Ｈ（Ａ）∩＾ｃｏＨ，而且，若Ｊ（Ａ）是余模理想，则Ｊ（Ａ＾ｃｏＨ）＝Ｊ＾Ｈ（Ａ）∩Ａ＾ｃｏＨ。     

［C，H］－Hopf模与模余代数的结构定理

本文首先利用ｃｏｉｎｔｅｇｒａｌ和ｃｏｃｌｅｆｔ模余代数概念，得到Ｈ为Ｈｏｐｆ代数当且仅当Ｈ作为Ｈ－模余代数是ｃｏｃｌｅｆｔ以及模余代数的一些性质．然后，设Ｃ为Ｈ－模余代数．令Ｃ＝Ｃ／Ｃｋｅｒε则有．最后，证明了结构定理：当Ｃ为ｃｏｃｌｅｆｔＨ－模余代数时，作为余代数有同构：Ｃ≌Ｃ×Ｈ     

G-旋模型场代数中的对偶定理

设Ｇ是有限群，　Ｈ是Ｇ的子群，Ｄ（Ｇ）为Ｇ的Ｄｏｕｂｌｅ代数，　Ｆ是　Ｇ－旋模型所对应的场代数．　本文考虑Ｄ（Ｇ）的Ｈｏｐｆ子代数Ｄ（Ｈ），证明了Ｆ的Ｄ（Ｈ）不变子空间ＡＨ是Ｃ＊－代数．Ｄ（Ｈ）存在Ｃ＊－表示，使得Ｄ（Ｈ）和ＡＨ互为换位子．     

Hopf代数的半单扩张与不变子环的同调维数

设H是域k上的有限维Hopf代数,A是左H-模代数,AH是A的H-不变子环.假定A/AH是半单扩张且A是平坦的右AH-模.如果H*是unimodular,且存在c∈C(A),使t·c=1.我们证明了WD(AH)=WD(A)=WD(A#H).此外,如果A是投射的左及右AH-模,则有LD(AH)=LD(A)=LD(A#H).     

H-separable Hopf Galois Extensions and Azumaya Algebra

1 IntroductionLet A/R be a ring extension with the common identity 1. A/R is said to be separable if theA-bimodule homomorphism of A @R A onto A defined by a @ 5-a6 splits. A separableextension over a non-commutative ring generalizes that over a commutative ring which wasdiscussed in [1]. Hirata introduced anOther kind of separable extensions called H-separabeones (see [2]). A/R is said to be H-separable if A @R A is isomorphic as an A-bimoduleto a direct sumrnand of A". riom {2, Theor…     

Gorenstein代数上的Hopf代数作用

令H是有限维Hopf代数，A是左H-模代数。本文证明了A是Gorenstein代数的充分必要条件。A^H也是Gorenstein代数的条件。它是Enochs EE,GarciaJJ和del RioA关于群作用相应的理论的推广，同时给出A/A^H是Frobenius扩张的条件。     

一类半单Hopf代数的结构

设k是特征为零的代数闭域,H是k上的pq~2维Frobenius型半单Hopf代数,其中p,q为不同的素数.本文证明了,如果p>q且H~*也是Frobenius型Hopf代数,则H是q~2维群代数A与A上p维Yetter-Drinfeld Hopf代数R的双积,即H≌R#A.作为例子,本文还证明了任意63维或68维的半单Hopf代数均为Frobenius型Hopf代数.     

On Galois Extension of Hopf Algebras

Let H be a cosemisimple Hopf algebra over a field k, and π ： A→ H be a surjective cocentral bialgebra homomorphism of bialgebras. The authors prove that if A is Galois over its coinvariants B=LH Ker π and B is a sub-Hopf algebra of A, then A is itself a Hopf algebra. This generalizes a result of Cegarra [3] on group-graded algebras.     

QF代数的Hopf代数作用

Ｈ是 Ｈｏｐｆ代数，Ａ是左 Ｈ－模代数，本文给出了当 Ａ是 ＱＦ代数时，ＡＨ也是 ＱＦ代数的一个条件．     

C~*-index of observable algebras in G-spin model

In two-dimensional lattice spin systems in which the spins take values in afinite group G,one can define a field algebra F which carries an action of a Hopf algebraD(G),the double algebra of G and moreover,an action of D(G;H),which is a subalgebraof D(G)determined by a subgroup H of G,so that F becomes a modular algebra.Theconcrete construction of D(G;H)-invariant subspace A_H in F is given.By constructingthe quasi-basis of conditional expectation γ_G of A_H onto A_G,the C~*-index of γ_G is exactlythe index of H in G.     

H-可分的Hopf Galois扩张与Azumaya代数

Let H be finite dimensional semisimple Hopf algebra over a field and A an H-module algebra,In this paper,we characterize and H-separable galois extension of an Azumaya algebra.Assuming that A/A^H is and H-separable extension,we prove that A/A^H is H^*-Galois and A^H is Azumaya if and only if A#H is and Azumaya Z-algebra,where Z is the center of A#H(not necessarily C(A)^H).     

On Hopf Galois Extension of Separable Algebras

In this paper, the classical Galois theory to the H*-Galois case is developed. Let H be a semisimple and cosemisimple Hopf algebra over a field k, A a left H-module algebra,and A/AHa right H*-Galois extension. The authors prove that, if AHis a separable kalgebra, then for any right coideal subalgebra B of H, the B-invariants A~B= {a ∈ A |b · a = ε(b)a, b∈ B} is a separable k-algebra. They also establish a Galois connection between right coideal subalgebras of H and separable subalgebras of A containing AHas in the classical case. The results are applied to the case H =(kG)*for a finite group G to get a Galois 1-1 correspondence.     

A NOTE ON THE GLOBAL DIMENSION OF SMASH PRODUCTS

Let H be a finite dimensional Hopf algebra over a field k, and A an H-module algebra. If H and H* are semisimple, then we prove that gl.dim(A#H) = gl.dim(A). The relationship between this result and Kaplansky's Fifth Conjecture is discussed.