arXiv subjects

Quanshui Wu

Publications and source records attributed to Quanshui Wu.

16 recordsLinked to original sources

arXiv2026

Homological properties of quantum groups governed by small quantum groups

We develop a general characteristic-free framework for studying the homological properties of a broad class of module-finite Hopf algebras. This framework makes it possible to reduce the study of the homological properties of many quantum groups at roots of unity and their multiparameter deformations to the study of the corresponding small quantum groups. For any affine Hopf algebra $H$ admitting a large central Hopf subalgebra $C$, we prove that its left homological integral space, in the sense of Lu-Wu-Zhang, is isomorphic as a bimodule to the left integral space of the identity fiber algebra, which is a finite-dimensional Hopf algebra. Consequently, $H$ is a symmetric Frobenius extension of $C$ if and only if the corresponding identity fiber algebra is unimodular and the square of the antipode of $H$ is inner, thus providing an effective criterion for the Calabi-Yau property of $H$. For a broad class of quantum groups at roots of unity, an appropriate large central Hopf subalgebra can be chosen such that the identity fiber algebra is the corresponding small quantum group. Therefore, some homological properties of these big quantum groups are governed by those of their corresponding small quantum groups. Assuming that the base field is algebraically closed, we prove that $H$ is unimodular if and only if, for some (equivalently, every) maximal ideal $\mathfrak{m}$ of $C$, the category of finite-dimensional representations of the fiber algebra at $\mathfrak{m}$ is unimodular in the sense of Yadav as a module category over the finite tensor category of finite-dimensional representations of the identity fiber algebra. As an application, we prove that all Andruskiewitsch-Angiono-Yakimov large quantum groups are affine noetherian unimodular Artin-Schelter Gorenstein Hopf algebras. We also give a necessary and sufficient condition for these large quantum groups to be Calabi-Yau.

math.QA↗

arXiv2026

Chevalley property of module-finite Hopf algebras and discriminant ideals

In this paper, we study the Chevalley property of Cayley-Hamilton Hopf algebras in the sense of De Concini-Procesi-Reshetikhin-Rosso using discriminant ideals. For any affine Cayley-Hamilton Hopf algebra $(H,C,\text{tr})$ whose identity fiber algebra has the Chevalley property, we prove that an irreducible $H$-module $V$ has the property that $V\otimes W$ is a completely reducible $H$-module for every irreducible $H$-module $W$ if and only if $V$ is annihilated by the lowest discriminant ideal of $(H,C,\text{tr})$, which establishes a bridge between the tensor-nondegenerate behaviour of the irreducible representations of $H$ and the lowest discriminant ideal of $(H,C,\text{tr})$. Using discriminant ideals, we prove that an affine Cayley-Hamilton Hopf algebra $(H,C,\text{tr})$ has the Chevalley property if and only if its identity fiber algebra $H/\mathfrak{m}_{\overline{\varepsilon}}H$ has the Chevalley property and all the discriminant ideals of $(H,C,\text{tr})$ are trivial, thereby resolving a question posed by Huang-Mi-Qi-Wu. Moreover, it is shown that the lowest discriminant subvariety $\mathcal{V}_{\ell}$ of the algebraic group $\operatorname{maxSpec}C$ is a closed subgroup, which reflects the rigid nature of $\mathcal{V}_{\ell}$ and is effective in determining the lowest discriminant subvarieties in certain examples of low GK dimension. This rigidity property provides a method, via the lowest discriminant ideals, for constructing a large family of Hopf algebras with the Chevalley property and finite GK dimension. The results are illustrated through applications to the big quantized Borel subalgebras at roots of unity and to certain Artin-Schelter Gorenstein Hopf algebras of low GK dimension. In particular, the framework yields (non-finite) tensor categories with the Chevalley property arising from some big quantum groups at roots of unity.

math.RA↗

arXiv2026

PI Artin--Schelter regular algebras of dimension 3 are unique factorization rings

We prove that all noetherian PI Artin--Schelter regular algebras of dimension $3$ are unique factorization rings. In a certain sense, this result is a noncommutative analogue to the fact that regular local rings of dimension 3 are UFDs. The fact constitutes a crucial component in the proof of the assertion that all regular local rings are UFDs, known as the Auslander--Buchsbaum theorem.

math.RA↗

arXiv2025

The ozone groups of PI Artin-Schelter regular algebras are abelian

We prove that the ozone group of any PI Artin-Schelter regular algebra is abelian, which answers a question of Chan-Gaddis-Won-Zhang. For any Calabi-Yau PI Artin-Schelter regular algebra, we prove that the homological determinant of its ozone group acting on it is trivial.

math.RA↗

arXiv2025

Connected Hopf Algebras that are Not Hopf Ore Extensions of Enveloping Algebras

We construct a family of connected Hopf algebras with finite Gelfand-Kirillov dimension, none of which is an iterated Hopf Ore extension of the universal enveloping algebra of its primitive part. This provides a negative answer to a question posed by Li and Zhou. It is also demonstrated that these connected Hopf algebras can be formulated as an iterated crossed product of enveloping algebras.

math.RA↗

arXiv2025

Commonly Graded Algebras and Their Homological Properties

In this article, we study bounded-below locally finite $\mathbb{Z}$-graded algebras, which are referred to as commonly graded algebras in literature. Commonly graded algebras have almost similar theory as that of connected graded algebras, but sometimes the results need different methods of proof. We give several characterizations of commonly graded AS-Gorenstein algebras, and show that any noetherian commonly graded AS-Gorenstein algebra admits a balanced dualizing complex. We then study (skew) Calabi-Yau properties of commonly graded algebras, and give an example of graded algebra which is skew Calabi-Yau in ungraded sense but not in graded sense. We demonstrate that a noetherian commonly graded algebra is AS-regular if and only if the bounded derived category of its finite-dimensional graded modules constitutes a ``twisted" Calabi-Yau category. At the end of the article, we prove that the Auslander-Buchsbaum formula, along with the Bass theorem and the No-Hole theorem hold for commonly graded algebras under appropriate conditions.

math.RA↗

arXiv2025

Chevalley property and discriminant ideals of Cayley-Hamilton Hopf Algebras

For any affine Hopf algebra $H$ which admits a large central Hopf subalgebra, $H$ can be endowed with a Cayley-Hamilton Hopf algebra structure in the sense of De Concini-Procesi-Reshetikhin-Rosso. The category of finite-dimensional modules over any fiber algebra of $H$ is proved to be an indecomposable exact module category over the tensor category of finite-dimensional modules over the identity fiber algebra $H/\mathfrak{m}_{\overline{\varepsilon}}H$ of $H$. For any affine Cayley-Hamilton Hopf algebra $(H,C,\text{tr})$ such that $H/\mathfrak{m}_{\overline{\varepsilon}}H$ has the Chevalley property, it is proved that if the zero locus of a discriminant ideal of $(H,C,\text{tr})$ is non-empty then it contains the orbit of the identity element of the affine algebraic group $\text{maxSpec}C$ under the left (or right) winding automorphism group action. Its proof relies on the fact that $H/\mathfrak{m}_{\overline{\varepsilon}}H$ has the Chevalley property if and only if the $\overline{\varepsilon}$-Chevalley locus of $(H,C)$ coincides with $\text{maxSpec}C$. Then, we provide a description of the zero locus of the lowest discriminant ideal of $(H,C,\text{tr})$. It is proved that the lowest discriminant ideal of $(H,C,\text{tr})$ is of level $\text{FPdim}(\text{Gr}(H/\mathfrak{m}_{\overline{\varepsilon}}H))+1$, where $\text{Gr}(H/\mathfrak{m}_{\overline{\varepsilon}}H)$ is the Grothendieck ring of the finite-dimensional Hopf algebra $H/\mathfrak{m}_{\overline{\varepsilon}}H$ and $\text{FPdim}(\text{Gr}(H/\mathfrak{m}_{\overline{\varepsilon}}H))$ is the Frobenius-Perron dimension of $\text{Gr}(H/\mathfrak{m}_{\overline{\varepsilon}}H)$. Some recent results of Mi-Wu-Yakimov about lowest discriminant ideals are generalized. We also prove that all the discriminant ideals are trivial if $H$ has the Chevalley property.

math.QA↗

arXiv2025

Numerical homological regularities over positively graded algebras

We study numerical regularities for complexes over noncommutative noetherian locally finite $\mathbb{N}$-graded algebras $A$ such as CM (cm)-regularity, Tor (tor)-regularity (Ext (ext)-regularity) and Ex (ex)-regularity, which are the supremum or infimum degrees of some associated canonical complexes. We show that for any right bounded complex $X$ with finitely generated cohomologies, the supremum degree of $R\underline{\text{Hom}}_A(X, A_0)$ coincides with the opposite of the infimum degree of $X$ if $A_0$ is semisimple. If $A$ has a balanced dualizing complex and $A_0$ is semisimple, we prove that the CM-regularity of $X$ coincides with the supremum degree of $R\underline{\text{Hom}}_A(A_0,X)$ for any left bounded complex $X$ with finitely generated cohomologies. Several inequalities concerning the numerical regularities and the supremum or infimum degree of derived Hom or derived tensor complexes are given for noncommutative noetherian locally finite $\mathbb{N}$-graded algebras. Some of these are generalizations of J\o rgensen's results on the inequalities between the CM-regularity and Tor-regularity, some are new even in the connected graded case. Conditions are given under which the inequalities become equalities by establishing two technical lemmas. Following Kirkman, Won and Zhang, we also use the numerical AS-regularity (resp. little AS-regularity) to study Artin-Schelter regular property (finite-dimensional property) for noetherian $\mathbb{N}$-graded algebras. We prove that the numerical AS-regularity of $A$ is zero if and only if that $A$ is an $\mathbb{N}$-graded AS-regular algebra under some mild conditions, which generalizes a result of Dong-Wu and a result of Kirkman-Won-Zhang. If $A$ has a balanced dualizing complex and $A_0$ is semisimple, we prove that the little AS-regularity of $A$ is zero if and only if $A$ is finite-dimensional.

math.RA↗

arXiv2025

Twisted Poincar\'e duality for orientable Poisson manifolds

We geometrize the constructions of twisted Poisson modules introduced by Luo-Wang-Wu, and Poisson chain complexes with coefficients in Poisson modules defined in the algebraic setting to the geometric setting of Poisson manifolds. We then prove that for any orientable Poisson manifold $M$, there is an explicit chain isomorphism between the Poisson cochain complex with coefficients in any Poisson geometric module and the Poisson chain complex with coefficients in the corresponding twisted Poisson geometric module, induced by a modular vector field of $M$. These are the geometric analogues of results obtained by Luo-Wang-Wu for smooth Poisson algebras with trivial canonical bundle. In particular, a version of twisted Poincar\'e duality is established between the Poisson homologies and the Poisson cohomologies of an orientable Poisson manifold with coefficients in an arbitrary vector bundle with a flat contravariant connection. This generalizes the duality theorems for orientable Poisson manifolds established by Evens-Lu-Weinstein, and by Xu.

math.DG↗

arXiv2024

Noncommutative resolutions of AS-Gorenstein isolated singularites

In this paper, we investigate noncommutative resolutions of (generalized) AS-Gorenstein isolated singularities. Noncommutative resolutions in graded case are achieved as the graded endomorphism rings of some finitely generated graded modules, which are seldom $\mathbb{N}$-graded algebras but bounded-below $\mathbb{Z}$-graded algebras. So, the paper works on locally finite bounded-below $\mathbb{Z}$-graded algebras. We first define and study noncommutative projective schemes after Artin-Zhang, and define noncommutative quasi-projective spaces as the base spaces of noncommutative projective schemes. The equivalences between noncommutative quasi-projective spaces are proved to be induced by so-called modulo-torsion-invertible bimodules, which is in fact a Morita-like theory at the quotient category level. Based on the equivalences, we propose a definition of noncommutative resolutions of generalized AS-Gorenstein isolated singularities, and prove that such noncommutative resolutions are generalized AS regular algebras. The center of any noncommutative resolution is isomorphic to the center of the original generalized AS-Gorenstein isolated singularity. In the final part we prove that a noncommutative resolution of an AS-Gorenstein isolated singularity of dimension $d$ is given by an MCM generator $M$ if and only if $M$ is a $(d-1)$-cluster tilting module. A noncommutative version of the Bondal-Orlov conjecture is also proved to be true in dimension 2 and 3.

math.RA↗

arXiv2024

Regular $\mathbb{Z}$-graded local rings and Graded Isolated Singularities

In this note we first study regular $\mathbb{Z}$-graded local rings. We characterize commutative noetherian regular $\mathbb{Z}$-graded local rings in similar ways as in the usual local case. Then, we characterize graded isolated singularity for a commutative $\mathbb{Z}$-graded semilocal algebra in terms of the global dimension of its associated noncommutative projective scheme. As a corollary, we obtain that a commutative affine $\mathbb{N}$-graded algebra generated in degree $1$ is a graded isolated singularity if and only if its associated noncommutative projective scheme is smooth; if and only if the category of coherent sheaves on its projective scheme has finite global dimension, which are known in literature.

math.AC↗

arXiv2023

The lowest discriminant ideal of a Cayley-Hamilton Hopf algebra

Discriminant ideals of noncommutative algebras $A$, which are module finite over a central sublagebra $C$, are key invariants that carry important information about $A$, such as the sum of the squares of the dimensions of its irreducible modules with a given central character. There has been substantial research on the computation of discriminants, but very little is known about the computation of discriminant ideals. In this paper we carry out a detailed investigation of the lowest discriminant ideals of Cayley-Hamilton Hopf algebras in the sense of De Concini, Reshetikhin, Rosso and Procesi, whose identity fiber algebras are basic. The lowest discriminant ideals are the most complicated ones, because they capture the most degenerate behaviour of the fibers in the exact opposite spectrum of the picture from the Azumaya locus. We provide a description of the zero sets of the lowest discriminant ideals of Cayley-Hamilton Hopf algebras in terms of maximally stable modules of Hopf algebras, irreducible modules that are stable under tensoring with the maximal possible number of irreducible modules with trivial central character. In important situations, this is shown to be governed by the actions of the winding automorphism groups. The results are illustrated with applications to the group algebras of central extensions of abelian groups, big quantum Borel subalgebras at roots of unity and quantum coordinate rings at roots of unity.

math.RT↗

arXiv2022

Generalized Koszul Algebra and Koszul Duality

We define generalized Koszul modules and rings and develop a generalized Koszul theory for $\mathbb{N}$-graded rings with the degree zero part noetherian semiperfect. This theory specializes to the classical Koszul theory for graded rings with degree zero part artinian semisimple developed by Beilinson-Ginzburg-Soergel and the ungraded Koszul theory for noetherian semiperfect rings developed by Green and Martin{é}z-Villa. Let $A$ be a left finite $\mathbb{N}$-graded ring generated in degree $1$ with $A_0$ noetherian semiperfect, $J$ be its graded Jacobson radical and $S=A/J$. By the Koszul dual of $A$ we mean the Yoneda Ext ring $\underline{\text{Ext}}_A^\bullet(S,S)$. If $A$ is a generalized Koszul ring and $M$ is a generalized Koszul module, then it is proved that the Koszul dual of the Koszul dual of $A$ is $\text{Gr}_J A$ and the Koszul dual of the Koszul dual of $M$ is $\text{Gr}_J M$. If $A$ is a locally finite algebra, then the following statements are proved to be equivalent: $A$ is generalized Koszul; the Koszul dual $\underline{\text{Ext}}_A^\bullet(S,S)$ of $A$ is (classically) Koszul; $\text{Gr}_J A$ is (classically) Koszul; the opposite ring $A^{op}$ of $A$ is generalized Koszul. It is also proved that if $A$ is generalized Koszul with finite global dimension then $A$ is generalized AS regular if and only if the Koszul dual of $A$ is self-injective.

math.RA↗

arXiv2022

Yoneda Ext-algebras of Takeuchi smash products

We prove that the Yoneda Ext-algebra of a Takeuchi smash product is the graded Takeuchi smash product of the Yoneda Ext-algebras of the two algebras or modules involved. As an application, we prove that graded Takeuchi smash products preserve Artin-Schelter regularity, and describe the Nakayama automorphism of the product.

math.RA↗

arXiv2021

Derived equivalences for a class of PI algebras

A description of tilting complexes is given for a class of PI algebras whose prime spectrum is canonically homeomorphic to the prime spectrum of its center. Some Sklyanin algebras are the kind of algebras considered. As an application, it is proved that any algebra derived equivalent to such kind of algebra, is Morita equivalent to it.

math.RA↗

arXiv2020

Poisson Dixmier-Moeglin equivalence from a topological point of view

In this paper, we provide some topological criteria for the Poisson Dixmier-Moeglin equivalence for $A$ in terms of the poset $({\rm P. spec A}, \subseteq)$ and the symplectic leaf or core stratification on its maximal spectrum. In particular, we prove that the Zariski topology of the Poisson prime spectrum and of each symplectic leaf or core can detect the Poisson Dixmier-Moeglin equivalence for any complex affine Poisson algebra. Moreover, we generalize the weaker version of the Poisson Dixmier-Moeglin equivalence for a complex affine Poisson algebra proved in [J. Bell, S. Launois, O.L. Sánchez, and B. Moosa, Poisson algebras via model theory and differential algebraic geometry, J. Eur. Math. Soc. (JEMS), 19(2017), no. 7, 2019-2049] to the general context of a commutative differential algebra.

math.RA↗