{"title":"A Uniqueness Property of (tau )-Exceptional Sequences","authors":"Eric J. Hanson, Hugh Thomas","doi":"10.1007/s10468-023-10226-w","DOIUrl":"10.1007/s10468-023-10226-w","url":null,"abstract":"<div><p>Recently, Buan and Marsh showed that if two complete <span>(tau )</span>-exceptional sequences agree in all but at most one term, then they must agree everywhere, provided the algebra is <span>(tau )</span>-tilting finite. They conjectured that the result holds without that assumption. We prove their conjecture. Along the way, we also show that the dimension vectors of the modules in a <span>(tau )</span>-exceptional sequence are linearly independent.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"461 - 468"},"PeriodicalIF":0.5,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48208544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Identities of Inverse Chevalley Type for the Graded Characters of Level-Zero Demazure Submodules over Quantum Affine Algebras of Type C","authors":"Takafumi Kouno, Satoshi Naito, Daniel Orr","doi":"10.1007/s10468-023-10221-1","DOIUrl":"10.1007/s10468-023-10221-1","url":null,"abstract":"<div><p>We provide identities of inverse Chevalley type for the graded characters of level-zero Demazure submodules of extremal weight modules over a quantum affine algebra of type <i>C</i>. These identities express the product <span>(e^{mu } text {gch} ~V_{x}^{-}(lambda ))</span> of the (one-dimensional) character <span>(e^{mu })</span>, where <span>(mu )</span> is a (not necessarily dominant) minuscule weight, with the graded character gch<span>(V_{x}^{-}(lambda ))</span> of the level-zero Demazure submodule <span>(V_{x}^{-}(lambda ))</span> over the quantum affine algebra <span>(U_{textsf{q}}(mathfrak {g}_{textrm{af}}))</span> as an explicit finite linear combination of the graded characters of level-zero Demazure submodules. These identities immediately imply the corresponding inverse Chevalley formulas for the torus-equivariant <i>K</i>-group of the semi-infinite flag manifold <span>(textbf{Q}_{G})</span> associated to a connected, simply-connected and simple algebraic group <i>G</i> of type <i>C</i>. Also, we derive cancellation-free identities from the identities above of inverse Chevalley type in the case that <span>(mu )</span> is a standard basis element <span>({varepsilon }_{k})</span> in the weight lattice <i>P</i> of <i>G</i>.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"429 - 460"},"PeriodicalIF":0.5,"publicationDate":"2023-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10468-023-10221-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44412270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Man-Wai Mandy Cheung, Juan Bosco Frías-Medina, Timothy Magee
{"title":"Quantization of Deformed Cluster Poisson Varieties","authors":"Man-Wai Mandy Cheung, Juan Bosco Frías-Medina, Timothy Magee","doi":"10.1007/s10468-023-10209-x","DOIUrl":"10.1007/s10468-023-10209-x","url":null,"abstract":"<div><p>Fock and Goncharov described a quantization of cluster <span>(mathcal {X})</span>-varieties (also known as <i>cluster Poisson varieties</i>) in Fock and Goncharov (Ann. Sci. Éc. Norm. Supér. <b>42</b>(6), 865–930 2009). Meanwhile, families of deformations of cluster <span>(mathcal {X})</span>-varieties were introduced in Bossinger et al. (Compos. Math. <b>156</b>(10), 2149–2206, 2020). In this paper we show that the two constructions are compatible– we extend the Fock-Goncharov quantization of <span>(mathcal {X})</span>-varieties to the families of Bossinger et al. (Compos. Math. <b>156</b>(10), 2149–2206, 2020). As a corollary, we obtain that these families and each of their fibers have Poisson structures. We relate this construction to the Berenstein-Zelevinsky quantization of <span>(mathcal {A})</span>-varieties (Berenstein and Zelevinsky, Adv. Math. <b>195</b>(2), 405–455, 2005). Finally, inspired by the counter-example to quantum positivity of the quantum greedy basis in Lee, et al. (Proc. Natl. Acad. Sci. <b>111</b>(27), 9712–9716, 2014), we compute a counter-example to quantum positivity of the quantum theta basis.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"381 - 427"},"PeriodicalIF":0.5,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45363995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A Note on Constructing Quasi Modules for Quantum Vertex Algebras from Twisted Yangians","authors":"Slaven Kožić, Marina Sertić","doi":"10.1007/s10468-023-10215-z","DOIUrl":"10.1007/s10468-023-10215-z","url":null,"abstract":"<div><p>In this note, we consider the twisted Yangians <span>(text {Y}(mathfrak {g}_N))</span> associated with the orthogonal and symplectic Lie algebras <span>(mathfrak {g}_N=mathfrak {o}_N,mathfrak {sp}_N)</span>. First, we introduce a certain subalgebra <span>(text {A}_c(mathfrak {g}_N))</span> of the double Yangian for <span>(mathfrak {gl}_N)</span> at the level <span>(cin mathbb {C})</span>, which contains the centrally extended <span>(text {Y}(mathfrak {g}_N))</span> at the level <i>c</i> as well as its vacuum module <span>(mathcal {M}_c(mathfrak {g}_N))</span>. Next, we employ its structure to construct examples of quasi modules for the quantum affine vertex algebra <span>(mathcal {V}_c(mathfrak {gl}_N))</span> associated with the Yang <i>R</i>-matrix. Finally, we use the description of the center of <span>(mathcal {V}_c(mathfrak {gl}_N))</span> to obtain explicit formulae for families of central elements for a certain completion of <span>(text {A}_c(mathfrak {g}_N))</span> and invariants of <span>(mathcal {M}_c(mathfrak {g}_N))</span>.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"363 - 380"},"PeriodicalIF":0.5,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46095062","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Module Categories of Small Radical Nilpotency","authors":"Shiping Liu, Youqi Yin","doi":"10.1007/s10468-023-10211-3","DOIUrl":"10.1007/s10468-023-10211-3","url":null,"abstract":"<div><p>This paper aims to initiate a study of the representation theory of representation-finite artin algebras in terms of the nilpotency of the radical of their module category. Firstly, we shall calculate this nilpotency explicitly for hereditary algebras of type <span>(mathbb {A}_n)</span> and for Nakayama algebras. Surprisingly, this nilpotency for a given algebra coincides with its Loewy length if and only if the algebra is a hereditary Nakayama algebra. Secondly, we shall find all artin algebras for which this nilpotency is equal to any given positive integer up to four and describe completely their module category.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"333 - 361"},"PeriodicalIF":0.5,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43244892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Drew Damien Duffield, Vincent Knibbeler, Sara Lombardo
{"title":"Wild Local Structures of Automorphic Lie Algebras","authors":"Drew Damien Duffield, Vincent Knibbeler, Sara Lombardo","doi":"10.1007/s10468-023-10208-y","DOIUrl":"10.1007/s10468-023-10208-y","url":null,"abstract":"<div><p>We study automorphic Lie algebras using a family of evaluation maps parametrised by the representations of the associative algebra of functions. This provides a descending chain of ideals for the automorphic Lie algebra which is used to prove that it is of wild representation type. We show that the associated quotients of the automorphic Lie algebra are isomorphic to twisted truncated polynomial current algebras. When a simple Lie algebra is used in the construction, this allows us to describe the local Lie structure of the automorphic Lie algebra in terms of affine Kac-Moody algebras.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"305 - 331"},"PeriodicalIF":0.5,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10468-023-10208-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47936091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Classifying Recollements of Derived Module Categories for Derived Discrete Algebras","authors":"Xiuli Bian","doi":"10.1007/s10468-023-10220-2","DOIUrl":"10.1007/s10468-023-10220-2","url":null,"abstract":"<div><p>We study a class of derived discrete Nakayama algebras. All indecomposable compact objects in the derived module category are determined and all recollements generated by the indecomposable compact exceptional objects are classified. It reveals that all such recollements are derived equivalent to stratifying recollements. As a byproduct, this confirms a question due to Xi for these recollements.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"279 - 304"},"PeriodicalIF":0.5,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43022067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Topologically Semiperfect Topological Rings","authors":"Leonid Positselski, Jan Šťovíček","doi":"10.1007/s10468-023-10217-x","DOIUrl":"10.1007/s10468-023-10217-x","url":null,"abstract":"<div><p>We define topologically semiperfect (complete, separated, right linear) topological rings and characterize them by equivalent conditions. We show that the endomorphism ring of a module, endowed with the finite topology, is topologically semiperfect if and only if the module is decomposable as an (infinite) direct sum of modules with local endomorphism rings. Then we study structural properties of topologically semiperfect topological rings and prove that their topological Jacobson radicals are strongly closed and the related topological quotient rings are topologically semisimple. For the endomorphism ring of a direct sum of modules with local endomorphism rings, the topological Jacobson radical is described explicitly as the set of all matrices of nonisomorphisms. Furthermore, we prove that, over a topologically semiperfect topological ring, all finitely generated discrete modules have projective covers in the category of modules, while all lattice-finite contramodules have projective covers in both the categories of modules and contramodules. We also show that the topological Jacobson radical of a topologically semiperfect topological ring is equal to the closure of the abstract Jacobson radical, and present a counterexample demonstrating that the topological Jacobson radical can be strictly larger than the abstract one. Finally, we discuss the problem of lifting idempotents modulo the topological Jacobson radical and the structure of projective contramodules for topologically semiperfect topological rings.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"245 - 278"},"PeriodicalIF":0.5,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10468-023-10217-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46266389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Epimorphic Quantum Subgroups and Coalgebra Codominions","authors":"Alexandru Chirvasitu","doi":"10.1007/s10468-023-10219-9","DOIUrl":"10.1007/s10468-023-10219-9","url":null,"abstract":"<div><p>We prove a number of results concerning monomorphisms, epimorphisms, dominions and codominions in categories of coalgebras. Examples include: (a) representation-theoretic characterizations of monomorphisms in all of these categories that when the Hopf algebras in question are commutative specialize back to the familiar necessary and sufficient conditions (due to Bien-Borel) that a linear algebraic subgroup be epimorphically embedded; (b) the fact that a morphism in the category of (cocommutative) coalgebras, (cocommutative) bialgebras, and a host of categories of Hopf algebras has the same codominion in any of these categories which contain it; (c) the invariance of the Hopf algebra or bialgebra (co)dominion construction under field extension, again mimicking the well-known corresponding algebraic-group result; (d) the fact that surjections of coalgebras, bialgebras or Hopf algebras are regular epimorphisms (i.e. coequalizers) provided the codomain is cosemisimple; (e) in particular, the fact that embeddings of compact quantum groups are equalizers in the category thereof, generalizing analogous results on (plain) compact groups; (f) coalgebra-limit preservation results for scalar-extension functors (e.g. extending scalars along a field extension <span>(Bbbk le Bbbk ')</span> is a right adjoint on the category of <span>(Bbbk )</span>-coalgebras).</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"219 - 244"},"PeriodicalIF":0.5,"publicationDate":"2023-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47951585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Stable Unital Bases, Hyperfocal Subalgebras and Basic Morita Equivalences","authors":"Tiberiu Coconeţ, Constantin-Cosmin Todea","doi":"10.1007/s10468-023-10216-y","DOIUrl":"10.1007/s10468-023-10216-y","url":null,"abstract":"<div><p>We investigate Conjecture 1.5 introduced by Barker and Gelvin (J. Gr. Theory <b>25</b>, 973–995 2022), which says that any source algebra of a <i>p</i>-block (<i>p</i> is a prime) of a finite group has the unit group containing a basis stabilized by the left and right actions of the defect group. We will reduce this conjecture to a similar statement about the bases of the hyperfocal subalgebras in the source algebras. We will also show that such unital bases of source algebras of two <i>p</i>-blocks, stabilized by the left and right actions of the defect group, are transported through basic Morita equivalences.</p></div>","PeriodicalId":50825,"journal":{"name":"Algebras and Representation Theory","volume":"27 1","pages":"203 - 218"},"PeriodicalIF":0.5,"publicationDate":"2023-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49266622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}