arXiv subjects

Martin Herschend

Publications and source records attributed to Martin Herschend.

11 recordsLinked to original sources

arXiv2024

Quiver Heisenberg algebras: a cubic analogue of preprojective algebras

In this paper we study a certain class of central extensions of preprojective algebras of quivers under the name quiver Heisenberg algebras (QHA). There are several classes of algebras introduced before by different researchers from different view points, which have the QHA as a special case. While these have mainly been studied in characteristic zero, we also study the case of positive characteristic. Our results show that the QHA is closely related to the representation theory of the corresponding path algebra in a similar way to the preprojective algebra. Among other things, one of our main results is that the QHA provides an exact sequence of bimodules over the path algebra of a quiver, which can be called the universal Auslander-Reiten sequence. Moreover, we show that the QHA provides minimal left and right approximations with respect to the powers of the radical functor. Consequently, we obtain a description of the QHA as a module over the path algebra, which in the Dynkin case, gives a categorification (as well as a generalization to the positive characteristic case) of the dimension formula by Etingof-Rains.

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arXiv2022

$n\mathbb{Z}$-cluster tilting subcategories for Nakayama algebras

$n\mathbb{Z}$-cluster tilting subcategories are an ideal setting for higher dimensional Auslander-Reiten theory. We give a complete classification of $n\mathbb{Z}$-cluster tilting subcategories of module categories of Nakayama algebras. In particular, we show that there are three kinds of Nakayama algebras that admit $n\mathbb{Z}$-cluster tilting subcategories: finite global dimension, selfinjective and non-Iwanaga-Gorenstein. Only the selfinjective ones can admit more than one $n\mathbb{Z}$-cluster tilting subcategory. It has been shown by the second author, that each such $n\mathbb{Z}$-cluster tilting subcategory induces an $n\mathbb{Z}$-cluster tilting subcategory of the corresponding singularity category. For each Nakayama algebra in our classification, we describe its singularity category, the canonical functor from its module category to its singularity category, and provide a complete comparison of $n\mathbb{Z}$-cluster tilting subcategories in the module category and the singularity category. This relies heavily of results by Shen, who described the singularity categories of all Nakayama algebras.

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arXiv2020

Classification of higher wide subcategories for higher Auslander algebras of type A

A subcategory $\mathscr{W}$ of an abelian category is called wide if it is closed under kernels, cokernels, and extensions. Wide subcategories are of interest in representation theory because of their links to other homological and combinatorial objects, established among others by Ingalls-Thomas and Marks-Šťovíček. If $d \geqslant 1$ is an integer, then Jasso introduced the notion of $d$-abelian categories, where kernels, cokernels, and extensions have been replaced by longer complexes. Wide subcategories can be generalised to this situation. Important examples of $d$-abelian categories arise as the $d$-cluster tilting subcategories $\mathscr{M}_{n,d}$ of $\operatorname{mod} A_n^{d-1}$, where $A_n^{d-1}$ is a higher Auslander algebra of type $A$ in the sense of Iyama. This paper gives a combinatorial description of the wide subcategories of $\mathscr{M}_{n,d}$ in terms of what we call non-interlacing collections.

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arXiv2020

Representation theory of Geigle-Lenzing complete intersections

Weighted projective lines, introduced by Geigle and Lenzing in 1987, are important objects in representation theory. They have tilting bundles, whose endomorphism algebras are the canonical algebras introduced by Ringel. The aim of this paper is to study their higher dimensional analogs. First, we introduce a certain class of commutative Gorenstein rings $R$ graded by abelian groups $L$ of rank $1$, which we call Geigle-Lenzing complete intersections. We study the stable category of Cohen-Macaulay representations $CM^LR$, which coincides with the singularity category $D_{sg}^L(R)$. We show that the stable category of $CM^LR$ is triangle equivalent to $D^b(mod A^{CM})$ for a finite dimensional algebra $A^{CM}$, which we call the CM-canonical algebra. As an application, we classify the $(R,L)$ that are Cohen-Macaulay finite. We also give sufficient conditions for $(R,L)$ to be $d$-Cohen-Macaulay finite in the sense of higher Auslander-Reiten theory. Secondly, we study a new class of non-commutative projective schemes in the sense of Artin-Zhang, i.e. the category $coh X=mod^LR/mod^L_0R$ of coherent sheaves on the Geigle-Lenzing projective space $X$. Geometrically this is the quotient stack $[(Spec R-{R_+})/Spec k[L]]$. We show that $D^b(coh X)$ is triangle equivalent to $D^b(mod A^{ca})$ for a finite dimensional algebra $A^{ca}$, which we call a $d$-canonical algebra. We study when $X$ is $d$-vector bundle finite, and when $X$ is derived equivalent to a $d$-representation infinite algebra in the sense of higher Auslander-Reiten theory. Our $d$-canonical algebras provide a rich source of $d$-Fano and $d$-anti-Fano algebras in non-commutative algebraic geometry. We also observe Orlov-type semiorthogonal decompositions of $D_{sg}^L(R)$ and $D^b(coh X)$.

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arXiv2019

Wide subcategories of $d$-cluster tilting subcategories

A subcategory of an abelian category is wide if it is closed under sums, summands, kernels, cokernels, and extensions. Wide subcategories provide a significant interface between representation theory and combinatorics. If $Φ$ is a finite dimensional algebra, then each functorially finite wide subcategory of $\operatorname{mod}( Φ)$ is of the form $ϕ_{ * }\big( \operatorname{mod}( Γ) \big)$ in an essentially unique way, where $Γ$ is a finite dimensional algebra and $Φ\stackrel{ ϕ}{ \longrightarrow } Γ$ is an algebra epimorphism satisfying $\operatorname{Tor}^{ Φ}_1( Γ,Γ) = 0$. Let ${\mathcal F} \subseteq \operatorname{mod}( Φ)$ be a $d$-cluster tilting subcategory as defined by Iyama. Then ${\mathcal F}$ is a $d$-abelian category as defined by Jasso, and we call a subcategory of ${\mathcal F}$ wide if it is closed under sums, summands, $d$-kernels, $d$-cokernels, and $d$-extensions. We generalise the above description of wide subcategories to this setting: Each functorially finite wide subcategory of ${\mathcal F}$ is of the form $ϕ_{ * }( {\mathcal G} )$ in an essentially unique way, where $Φ\stackrel{ ϕ}{ \longrightarrow } Γ$ is an algebra epimorphism satisfying $\operatorname{Tor}^{ Φ}_d( Γ,Γ) = 0$, and ${\mathcal G} \subseteq \operatorname{mod}( Γ)$ is a $d$-cluster tilting subcategory. We illustrate the theory by computing the wide subcategories of some $d$-cluster tilting subcategories ${\mathcal F} \subseteq \operatorname{mod}( Φ)$ over algebras of the form $Φ= kA_m / (\operatorname{rad}\,kA_m )^{ \ell }$.

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arXiv2018

$n$-exangulated categories

For each positive integer $n$ we introduce the notion of $n$-exangulated categories as higher dimensional analogues of extriangulated categories defined by Nakaoka-Palu. We characterize which $n$-exangulated categories are $n$-exact in the sense of Jasso and which are $(n+2)$-angulated in the sense of Geiss-Keller-Oppermann. For extriangulated categories with enough projectives and injectives we introduce the notion of $n$-cluster tilting subcategories and show that under certain conditions such $n$-cluster tilting subcategories are $n$-exangulated.

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arXiv2012

n-Representation infinite algebras

From the viewpoint of higher dimensional Auslander-Reiten theory, we introduce a new class of finite dimensional algebras of global dimension n, which we call n-representation infinite. They are a certain analog of representation infinite hereditary algebras, and we study three important classes of modules: n-preprojective, n-preinjective and n-regular modules. We observe that their homological behaviour is quite interesting. For instance they provide first examples of algebras having infinite Ext^1-orthogonal families of modules. Moreover we give general constructions of n-representation infinite algebras. Applying Minamoto's theory on Fano algebras in non-commutative algebraic geometry, we describe the category of n-regular modules in terms of the corresponding preprojective algebra. Then we introduce n-representation tame algebras, and show that the category of n-regular modules decomposes into the categories of finite dimensional modules over localizations of the preprojective algebra. This generalizes the classical description of regular modules over tame hereditary algebras. As an application, we show that the representation dimension of an n-representation tame algebra is at least n+2.

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arXiv2010

Selfinjective quivers with potential and 2-representation-finite algebras

We study quivers with potential (QPs) whose Jacobian algebras are finite dimensional selfinjective. They are an analogue of the `good QPs' studied by Bocklandt whose Jacobian algebras are 3-Calabi-Yau. We show that 2-representation-finite algebras are truncated Jacobian algebras of selfinjective QPs, which are factor algebras of Jacobian algebras by certain sets of arrows called cuts. We show that selfinjectivity of QPs is preserved under successive mutation with respect to orbits of the Nakayama permutation. We give a sufficient condition for all truncated Jacobian algebras of a fixed QP to be derived equivalent. We introduce planar QPs which provide us with a rich source of selfinjective QPs.

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arXiv2010

n-representation-finite algebras and twisted fractionally Calabi-Yau algebras

In this short paper, we study $n$-representation-finite algebras from the viewpoint of the fractionally Calabi-Yau property. We shall show that all $n$-representation-finite algebras are twisted fractionally Calabi-Yau. We also show that for any $\ell>0$, twisted $\frac{n(\ell-1)}{\ell}$-Calabi-Yau algebras of global dimension at most $n$ are $n$-representation-finite. As an application, we give a construction of $n$-representation-finite algebras using the tensor product.

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arXiv2009

Solution to the Clebsch-Gordan problem for string algebras

The category of modules over a string algebra is equipped with a tensor product defined point-wise and arrow-wise in terms of the underlying quiver. In the present article we investigate how this tensor product interacts with the classification of indecomposables. We apply the results obtained to solve the Clebsch-Gordan problem for string algebras. Moreover, we describe the corresponding representation ring and tensor ideals in the module category.

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arXiv2008

On the representation ring of the polynomial algebra over a perfect field

We consider the tensor product of modules over the polynomial algebra corresponding to the usual tensor product of linear operators. We present a general description of the representation ring in case the ground field k is perfect. It is made explicit in the special cases when k is real closed respectively algebraically closed. Furthermore, we discuss the generalisation of this problem to representations of quivers. In particular the representation ring of quivers of extended Dynkin type A is provided.

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