Osamu Iyama
We will study the relationship of quite different object in the theory of artin algebras, namely Auslander-regular rings of global dimension two, torsion theories, $τ$-categories and almost abelian categories. We will apply our results to characterization problems of Auslander-Reiten quivers.
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Gorenstein homological algebra is a kind of relative homological algebra which has been developed to a high level since more than four decades. In this report we review the basic theory of Gorenstein homological algebra of artin algebras. It is hoped that such a theory will help to understand the famous Gorenstein symmetric conjecture of artin algebras. With only few exceptions all the results in this report are contained in the existing literature. We have tried to keep the exposition as self-contained as possible. This report can be viewed as a preparation for learning the newly developed th…
On the homological conjectures for Artin algebras
本文证明Tachikawa第二猜想蕴含Artin代数的Auslander-Reiten猜想，并通过二重平凡扩张及已知关系，揭示多个重要猜想等价，且第二猜想蕴含第一猜想。
We prove that for a Frobenius extension, a module over the extension ring is Gorenstein projective if and only if its underlying module over the base ring is Gorenstein projective. For a separable Frobenius extension between Artin algebras, we obtain that the extension algebra is CM-finite (resp. CM-free) if and only if so is the base algebra. Furthermore, we prove that the reprensentation dimension of Artin algebras is invariant under separable Forbenius extensions.
This paper studies the homological determinants and Nakayama automorphisms of not-necessarily-noetherian $m$-Koszul twisted Calabi-Yau or, equivalently, $m$-Koszul Artin-Schelter regular, algebras. Dubois-Violette showed that such an algebra is isomorphic to a derivation quotient algebra D(w,i) for a unique-up-to-scalar-multiples twisted superpotential w in a tensor power of some vector space V. By definition, D(w,i) is the quotient of the tensor algebra TV by the ideal generated by all i-th order left partial derivatives of w. We identify the group of graded algebra automorphisms of D(w,i) wi…
Homological regularities and concavities
本文研究非交换代数的同调正则性，引入凹性和Artin-Schelter正则性两个新不变量，并建立判定诺特连通分次代数是否为Artin-Schelter正则的准则。
Homological Integrals for Weak Hopf Algebras
本文引入了无限维弱Hopf代数的同调积分概念，并借此证明了若干结构定理，包括Artin-Schelter性质与Van den Bergh条件的等价性、对极映射的自动可逆性，以及关于仿射中心上有限弱Hopf代数的分解定理。
Let $R$ and $S$ be rings and $_Rω_S$ a semidualizing bimodule. We prove that there exists a Morita equivalence between the class of $\infty$-$ω$-cotorsionfree modules and a subclass of the class of $ω$-adstatic modules. Also we establish the relation between the relative homological dimensions of a module $M$ and the corresponding standard homological dimensions of ${\rm Hom}(ω,M)$. By investigating the properties of the Bass injective dimension of modules (resp. complexes), we get some equivalent characterizations of semi-tilting modules (resp. Gorenstein artin algebras). Finally we obtain a …
Homological properties of some quantum Heisenberg algebras
本文研究一类依赖参数q和多项式f、g的量子广义海森堡代数的Koszul、Artin-Schelter正则与Calabi-Yau等同调性质，并证明在特定条件下这些代数满足上述性质。
We consider homological finiteness properties $FP_n$ of certain $\mathbb{N}$-graded Lie algebras. After proving some general results, see Theorem A, Corollary B and Corollary C, we concentrate on a family that can be considered as the Lie algebra version of the generalized Bestvina-Brady groups associated to a graph $Γ$. We prove that the homological finiteness properties of these Lie algebras can be determined in terms of the graph in the same way as in the group case. In the last version we have corrected some missprints, in particular the statement of Theorem D (from $n-1$-acyclicity to $n-…
The ozone groups of PI Artin-Schelter regular algebras are abelian
本文证明了 PI Artin-Schelter 正则代数的 ozone 组是交换群，并展示了其同调确定的平凡性。
Homological theory of orthogonal modules
本研究从稳定模范畴视角研究自入射Artin代数上的有限生成正交生成元，建立M-相对稳定范畴的粘合、刻画紧对象，给出Tachikawa第二猜想的等价刻画，还引入Gorenstein-Morita代数并证明Nakayama猜想对其成立。
We investigate homological and ring-theoretic properties of universal quantum linear groups that coact on Artin-Schelter regular algebras A(n) of global dimension 2, especially with central homological codeterminant (or central quantum determinant). As classified by Zhang, the algebras A(n) are connected \N-graded algebras that are finitely generated by n indeterminants of degree 1, subject to one quadratic relation. In the case when the homological codeterminant of the coaction is trivial, we show that the quantum group of interest, defined independently by Manin and by Dubois-Violette and La…
We study homological properties and rigidity of group coactions on Artin-Schelter regular algebras.
We introduce a new method to construct 4-dimensional Artin-Schelter regular algebras as normal extensions of (not necessarily noetherian) 3-dimensional ones. The method produces large classes of new 4-dimensional Artin-Schelter regular algebras. When applied to a 3-Calabi-Yau algebra our method produces a flat family of central extensions of it that are 4-Calabi-Yau, and all 4-Calabi-Yau central extensions having the same generating set as the original 3-Calabi-Yau algebra arise in this way. Each normal extension has the same generators as the original 3-dimensional algebra, and its relations …
New invariants of stable equivalences of algebras
本文证明了无结点及正$\ u$-支配维数的Artin代数在稳定等变下保持同调不变量，并验证了两类代数关于稳定等变的Auslander--Reiten猜想。
As a dual of the Auslander transpose of modules, we introduce and study the cotranspose of modules with respect to a semidualizing module $C$. Then using it we introduce $n$-$C$-cotorsionfree modules, and show that $n$-$C$-cotorsionfree modules possess many dual properties of $n$-torsionfree modules. In particular, we show that $n$-$C$-cotorsionfree modules are useful in characterizing the Bass class and investigating the approximation theory for modules. Moreover, we study $n$-cotorsionfree modules over artin algebras and answer negatively an open question of Huang and Huang posed in 2012.
Artin-Schelter Gorenstein property of Hopf Galois extensions
本文探讨了Hopf Galois扩展的AS Gorenstein性质，证明了在特定条件下该性质可被继承，并揭示了AS Gorenstein Hopf代数的投射维数单体不变量特性。
Let $Λ$ be an artin algebra and $\mathfrak{A}$ a two-sided idempotent ideal of $Λ$, that is, $\mathfrak{A}$ is the trace of a projective $Λ$-module $P$ in $Λ$. We consider the categories of finitely generated modules over the associated rings $Λ/\mathfrak{A}, Λ$ and $Γ=\mathrm{End}_Λ(P)^{op}$ and study the relationship between their homological properties via the Igusa-Todorov functions.
We study the structural and homological properties of graded Artinian modules over generalized Weyl algebras (GWAs), and this leads to a decomposition result for the category of graded Artinian modules. Then we define and examine a category of graded modules analogous to the BGG category O. We discover a condition on the data defining the GWA that ensures O has a system of projective generators. Under this condition, O has nice representation-theoretic properties. There is also a decomposition result for O. Next, we give a necessary condition for there to be a strongly graded Morita equivalenc…
We study quadratic algebras over a field $\textbf{k}$. We show that an $n$-generated PBW algebra $A$ has finite global dimension and polynomial growth \emph{iff} its Hilbert series is $H_A(z)= 1 /(1-z)^n$. Surprising amount can be said when the algebra $A$ has \emph{quantum binomial relations}, that is the defining relations are nondegenerate square-free binomials $xy-c_{xy}zt$ with non-zero coefficients $c_{xy}\in \textbf{k}$. In this case various good algebraic and homological properties are closely related. The main result shows that for an $n$-generated quantum binomial algebra $A$ the fol…
Artin-Schelter Regular Algebras
本文综述了作为非交换射影几何核心对象的 Artin-Schelter 正则代数，回顾其早期基础成果并梳理近30年研究的主要主题。
Nakayama automorphisms of graded double Ore extensions of Koszul Artin-Schelter regular algebras with nontrivial skew derivations
本文研究Koszul Artin-Schelter正则代数的分次双重Ore扩张，通过构造极小自由预解证明其保持Koszul性质，并引入$ς$-散度同调不变量精确刻画中山自同构，进而构造扭曲超势实现导子商代数同构。
For any ring R the category of monomorphisms is a full subcategory of the morphsim category over R, where the latter is equivalent to the module category of the triangular matrix ring with entries the ring R. In this work, we consider the monomorphism category as a full subcategory of the module category over the Morita ring with all entries the ring R and zero bimodule homomorphisms. This approach provides an interesting link between Morita rings and monomorphism categories. The aim of this paper is two-fold. First, we construct Gorenstein-projective modules over Morita rings with zero bimodu…
We discuss certain homological properties of graded algebras whose trivial modules admit non-pure resolutions. Such algebras include both of Artin-Schelter regular algebras of types (12221) and (13431). Under certain conditions, a module with non-pure resolution is decomposed to form an extension by two modules with pure resolutions.
In this paper, we study homological properties of twisted tensor products of connected graded algebras. We focus on the Ext-algebras of twisted tensor products with a certain form of twisting maps firstly. We show those Ext-algebras are also twisted tensor products, and depict the twisting maps for such Ext-algebras in-depth. With those preparations, we describe Nakayama automorphisms of twisted tensor products of noetherian Artin-Schelter regular algebras.
Finitistic dimension via modules over the singularity category
该研究结合相关结果与方法，证明Artin代数的有限维数有限性是其对立代数的奇点不变量，且有限有限维数可沿奇点范畴的特定完全忠实函子下降，补充了已有相关工作。
Gorenstein homological invariants and monoidal model categories of Hopf algebras
本文研究了霍普夫代数的戈林斯泰因同调不变量，并证明了在特定条件下霍普夫代数的模块范畴是单向模型范畴。
Singular equivalences and homological conjectures
通过中心化子矩阵代数的奇异范畴和奇异等价，验证了Auslander-Reiten和Cartan行列式猜想，进而证明所有经典同调猜想对域上中心化子矩阵代数成立。
Rank two Artin-Schelter regular algebras and non commuting derivations
本文研究由满足特定交换关系的导子 $Δ$ 和 $Γ$ 构造的代数 $(A,\ast)$，证明其过滤半经典极限为秩二泊松结构，并在每个至少四维的维度上给出 Artin-Schelter 正则代数和 Calabi-Yau 代数的多参数族新例子。
Auslander-type conditions and weakly Gorenstein algebras
本文在Auslander型条件下用Gorenstein投射模给出弱Gorenstein代数的等价刻画，并将Auslander–Reiten猜想约化为左右弱Gorenstein条件的判定。
Homological properties of quantum groups governed by small quantum groups
本文建立无特征框架，将单位根处量子群的同调性质归结为小量子群，并证明大量子群为Artin-Schelter Gorenstein及给出Calabi-Yau判据。
Twisting Manin's universal quantum groups and comodule algebras
本文引入量子对称等价概念，证明多种正则性与 Frobenius 性质在 Morita-Takeuchi 等价下不变，并刻画了 2-上循环扭曲对 Koszul 对偶、超势代数及 Hochschild 上同调环有限生成性的保持性质。
We determine the possible Hilbert functions of graded rank one torsion free modules over three dimensional Artin-Schelter regular algebras. It turns out that, as in the commutative case, they are related to Castelnuovo functions. From this we obtain an intrinsic proof that the space of torsion free rank one modules on a non-commutative projective plane is connected. A different proof of this fact, based on deformation theoretic methods and the known commutative case has recently been given by Nevins and Stafford. For the Weyl algebra it was proved by Wilson.
Exact Categories and Homological Foundations of Non-Commutative n-ary Gamma. Semirings
本文提出非交换n元Gamma半环的同调基础，构建了非交换衍生Gamma几何框架，实现了Gamma代数中两个不同方向的统一。
Certain sufficient homological and ring-theoretical conditions are given for a Hopf algebra to have bijective antipode with applications to noetherian Hopf algebras regarding their homological behaviors.
Given an additive category $\mathcal{C}$ and an integer $n\geqslant 2$. We form a new additive category $\mathcal{C}[ε]^n$ consisting of objects $X$ in $\mathcal{C}$ equipped with an endomorphism $ε_X$ satisfying ${ε^n_X}=0$. First, using the descriptions of projective and injective objects in $\mathcal{C}[ε]^n$, we not only establish a connection between Gorenstein flat modules over a ring $R$ and $R[t]/(t^n)$, but also prove that an Artinian algebra $R$ satisfies some homological conjectures if and only if so does $R[t]/(t^n)$. Then we show that the corresponding homotopy category $\K(\mathc…
In this paper we work with unital twisted partial actions. We investigate ring theoretic properties of partial crossed products as artinianity, noetherianity, perfect property, semilocalproperty, semiprimary property and we also study the Krull dimension. Moreover, we consider triangular matrix representation of partial skew group rings, weak and global dimensions of partial crossed products Also we study when the partial crossed products are Frobenius and symmetric algebras.
Numerical homological regularities over positively graded algebras
本文研究正分次代数上复形的多种数值同调正则性，证明其与导出 Hom 复形极值次数的一致性，建立若干不等式及其成为等式的条件，并利用数值 AS-正则性刻画 AS-正则性质和有限维性质。
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