Pub Date : 2025-09-29DOI: 10.1016/j.jpaa.2025.108100
Mark Colarusso , Sam Evens
<div><div>Let <span><math><mi>G</mi><mo>=</mo><mi>G</mi><mi>L</mi><mo>(</mo><mi>n</mi><mo>)</mo></math></span> be the <span><math><mi>n</mi><mo>×</mo><mi>n</mi></math></span> complex general linear group and let <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> be its flag variety. The standard Borel subgroup <em>B</em> of upper triangular matrices acts on the product <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup></math></span> diagonally with finitely many orbits. In this paper, we study the <em>B</em>-orbits on the subvarieties <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>, where <span><math><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> is the <em>B</em>-orbit on <span><math><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup></math></span> containing the line through the origin in the direction of the <em>i</em>-th standard basis vector of <span><math><msup><mrow><mi>C</mi></mrow><mrow><mi>n</mi></mrow></msup></math></span>. For each <span><math><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>n</mi></math></span>, we construct a bijection between <em>B</em>-orbits on <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> and certain pairs of Schubert cells in <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>. We also show that this bijection can be used to understand the Richardson-Springer monoid action on such <em>B</em>-orbits in terms of the classical monoid action of the symmetric group on itself. We also develop combinatorial models of these orbits and use these models to compute exponential generating functions for the sequences <span><math><msub><mrow><mo>{</mo><mo>|</mo><mi>B</mi><mo>﹨</mo><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>)</mo><mo>|</mo><mo>}</mo></mrow><mrow><mi>n</mi><mo>≥</mo><mn>1</mn></mrow></msub></math></span> and <span><math><msub><mrow><mo>{</mo><mo>|</mo><mi>B</mi><mo>﹨</mo><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup><mo>)</mo><mo>|</mo><mo>}</mo></mrow><mrow><mi>n</mi><mo>≥</mo><mn>1</mn></mrow></msub></math></span>. In the sequel to this paper, we use the results of this paper to construct a correspondence between <em>B</em>-orbits on <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn>
{"title":"Orbits on a product of two flags and a line and the Bruhat order, I","authors":"Mark Colarusso , Sam Evens","doi":"10.1016/j.jpaa.2025.108100","DOIUrl":"10.1016/j.jpaa.2025.108100","url":null,"abstract":"<div><div>Let <span><math><mi>G</mi><mo>=</mo><mi>G</mi><mi>L</mi><mo>(</mo><mi>n</mi><mo>)</mo></math></span> be the <span><math><mi>n</mi><mo>×</mo><mi>n</mi></math></span> complex general linear group and let <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> be its flag variety. The standard Borel subgroup <em>B</em> of upper triangular matrices acts on the product <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup></math></span> diagonally with finitely many orbits. In this paper, we study the <em>B</em>-orbits on the subvarieties <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span>, where <span><math><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> is the <em>B</em>-orbit on <span><math><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup></math></span> containing the line through the origin in the direction of the <em>i</em>-th standard basis vector of <span><math><msup><mrow><mi>C</mi></mrow><mrow><mi>n</mi></mrow></msup></math></span>. For each <span><math><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>n</mi></math></span>, we construct a bijection between <em>B</em>-orbits on <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> and certain pairs of Schubert cells in <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>. We also show that this bijection can be used to understand the Richardson-Springer monoid action on such <em>B</em>-orbits in terms of the classical monoid action of the symmetric group on itself. We also develop combinatorial models of these orbits and use these models to compute exponential generating functions for the sequences <span><math><msub><mrow><mo>{</mo><mo>|</mo><mi>B</mi><mo>﹨</mo><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msub><mrow><mi>O</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>)</mo><mo>|</mo><mo>}</mo></mrow><mrow><mi>n</mi><mo>≥</mo><mn>1</mn></mrow></msub></math></span> and <span><math><msub><mrow><mo>{</mo><mo>|</mo><mi>B</mi><mo>﹨</mo><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup><mo>)</mo><mo>|</mo><mo>}</mo></mrow><mrow><mi>n</mi><mo>≥</mo><mn>1</mn></mrow></msub></math></span>. In the sequel to this paper, we use the results of this paper to construct a correspondence between <em>B</em>-orbits on <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>×</mo><msup><mrow><mi>P</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108100"},"PeriodicalIF":0.8,"publicationDate":"2025-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222120","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-25DOI: 10.1016/j.jpaa.2025.108099
Henry Bradford
In [4] Bou-Rabee and Seward constructed examples of finitely generated residually finite groups G whose residual finiteness growth function can be at least as fast as any prescribed function. In this note we describe a modified version of their construction, which allows us to give a complementary upper bound on . As such, every nondecreasing function at least is close to the residual finiteness growth function of some finitely generated group. We also have similar result for the full residual finiteness growth function and for the divisibility function.
{"title":"On the spectrum of residual finiteness growth functions","authors":"Henry Bradford","doi":"10.1016/j.jpaa.2025.108099","DOIUrl":"10.1016/j.jpaa.2025.108099","url":null,"abstract":"<div><div>In <span><span>[4]</span></span> Bou-Rabee and Seward constructed examples of finitely generated residually finite groups <em>G</em> whose residual finiteness growth function <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>G</mi></mrow></msub></math></span> can be at least as fast as any prescribed function. In this note we describe a modified version of their construction, which allows us to give a complementary upper bound on <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>G</mi></mrow></msub></math></span>. As such, every nondecreasing function at least <span><math><mi>exp</mi><mo></mo><mo>(</mo><mi>n</mi><mi>log</mi><mo></mo><msup><mrow><mo>(</mo><mi>n</mi><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><mi>log</mi><mo></mo><mi>log</mi><mo></mo><msup><mrow><mo>(</mo><mi>n</mi><mo>)</mo></mrow><mrow><mn>1</mn><mo>+</mo><mi>ϵ</mi></mrow></msup><mo>)</mo></math></span> is close to the residual finiteness growth function of some finitely generated group. We also have similar result for the <em>full</em> residual finiteness growth function and for the divisibility function.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108099"},"PeriodicalIF":0.8,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-19DOI: 10.1016/j.jpaa.2025.108096
Yanjie Li , Shizhuo Zhang
Let be 2g dimensional quadrics in and let Y be the smooth intersection . We associate the linear subspaces in Y with vector bundles on the hyperelliptic curve C of genus g via categorical methods. As an application, we give a different proof of the classification of line bundles and stable bundles of rank 2 on hyperelliptic curves given by Desale and Ramanan. When , we show that the projection functor induces a closed embedding into the moduli space of stable bundles on C of rank 4 of fixed determinant.
{"title":"Linear subspaces of the intersection of two quadrics via Kuznetsov component","authors":"Yanjie Li , Shizhuo Zhang","doi":"10.1016/j.jpaa.2025.108096","DOIUrl":"10.1016/j.jpaa.2025.108096","url":null,"abstract":"<div><div>Let <span><math><msub><mrow><mi>Q</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>(</mo><mi>i</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>)</mo></math></span> be 2<em>g</em> dimensional quadrics in <span><math><msup><mrow><mi>P</mi></mrow><mrow><mn>2</mn><mi>g</mi><mo>+</mo><mn>1</mn></mrow></msup></math></span> and let <em>Y</em> be the smooth intersection <span><math><msub><mrow><mi>Q</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>∩</mo><msub><mrow><mi>Q</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>. We associate the linear subspaces in <em>Y</em> with vector bundles on the hyperelliptic curve <em>C</em> of genus <em>g</em> via categorical methods. As an application, we give a different proof of the classification of line bundles and stable bundles of rank 2 on hyperelliptic curves given by Desale and Ramanan. When <span><math><mi>g</mi><mo>=</mo><mn>3</mn></math></span>, we show that the projection functor induces a closed embedding <span><math><mi>α</mi><mo>:</mo><mi>Y</mi><mo>→</mo><mi>S</mi><msubsup><mrow><mi>U</mi></mrow><mrow><mi>C</mi></mrow><mrow><mi>s</mi></mrow></msubsup><mo>(</mo><mn>4</mn><mo>,</mo><mi>h</mi><mo>)</mo></math></span> into the moduli space of stable bundles on <em>C</em> of rank 4 of fixed determinant.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108096"},"PeriodicalIF":0.8,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145120999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-19DOI: 10.1016/j.jpaa.2025.108098
Kamal Aziziheris , Necat Gorentas , Zinah Naser Sulaiman
Let be the average degree of irreducible characters of G with odd degree. It has been proved that if , then G is a solvable group. On the other hand, let be the average degree of linear characters and irreducible characters of G with even degree. It has been shown that if , then G is a solvable group. In this paper, we improve these bounds and we show that if G is a finite group with , then either G is a solvable group or G has a chief factor isomorphic to . Also, we prove that if G is a finite group with , then either G is a solvable group or all minimal normal subgroups of G are abelian or isomorphic to . Clearly, these bounds are the best.
{"title":"On the average degree of characters with odd or even degrees","authors":"Kamal Aziziheris , Necat Gorentas , Zinah Naser Sulaiman","doi":"10.1016/j.jpaa.2025.108098","DOIUrl":"10.1016/j.jpaa.2025.108098","url":null,"abstract":"<div><div>Let <span><math><msub><mrow><mi>acd</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mo>′</mo></mrow></msup></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo></math></span> be the average degree of irreducible characters of <em>G</em> with odd degree. It has been proved that if <span><math><msub><mrow><mi>acd</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mo>′</mo></mrow></msup></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo><mo><</mo><msub><mrow><mi>acd</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mo>′</mo></mrow></msup></mrow></msub><mo>(</mo><msub><mrow><mtext>A</mtext></mrow><mrow><mn>5</mn></mrow></msub><mo>)</mo><mo>=</mo><mn>3</mn></math></span>, then <em>G</em> is a solvable group. On the other hand, let <span><math><msub><mrow><mi>acd</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo></math></span> be the average degree of linear characters and irreducible characters of <em>G</em> with even degree. It has been shown that if <span><math><msub><mrow><mi>acd</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo><mo><</mo><msub><mrow><mi>acd</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><msub><mrow><mtext>A</mtext></mrow><mrow><mn>5</mn></mrow></msub><mo>)</mo><mo>=</mo><mn>5</mn><mo>/</mo><mn>2</mn></math></span>, then <em>G</em> is a solvable group. In this paper, we improve these bounds and we show that if <em>G</em> is a finite group with <span><math><msub><mrow><mi>acd</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mo>′</mo></mrow></msup></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo><mo><</mo><msub><mrow><mi>acd</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mo>′</mo></mrow></msup></mrow></msub><mo>(</mo><mrow><mi>PSL</mi></mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>7</mn><mo>)</mo><mo>)</mo><mo>=</mo><mn>7</mn><mo>/</mo><mn>2</mn></math></span>, then either <em>G</em> is a solvable group or <em>G</em> has a chief factor isomorphic to <span><math><msub><mrow><mtext>A</mtext></mrow><mrow><mn>5</mn></mrow></msub></math></span>. Also, we prove that if <em>G</em> is a finite group with <span><math><msub><mrow><mi>acd</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo><mo><</mo><msub><mrow><mi>acd</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><mrow><mi>PSL</mi></mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>8</mn><mo>)</mo><mo>)</mo><mo>=</mo><mn>9</mn><mo>/</mo><mn>2</mn></math></span>, then either <em>G</em> is a solvable group or all minimal normal subgroups of <em>G</em> are abelian or isomorphic to <span><math><msub><mrow><mtext>A</mtext></mrow><mrow><mn>5</mn></mrow></msub></math></span>. Clearly, these bounds are the best.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108098"},"PeriodicalIF":0.8,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145121044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-19DOI: 10.1016/j.jpaa.2025.108097
Robert Auffarth , Jorge Duque Franco
The rank ρ of the Néron-Severi group of a complex torus X of dimension g satisfies . The degree of the extension field generated over by the entries of a period matrix of X imposes constraints on its Picard number ρ and, consequently, on the structure of X. In this paper, we show that when is 2, 3, or 4, the Picard number ρ is necessarily large. Moreover, for an abelian variety X of dimension g with , we establish a structure-type result: X must be isogenous to , where E is an elliptic curve without complex multiplication. In this case, the Picard number satisfies . As a byproduct, we obtain that if is odd, then .
{"title":"On the Picard number and the extension degree of period matrices of complex tori","authors":"Robert Auffarth , Jorge Duque Franco","doi":"10.1016/j.jpaa.2025.108097","DOIUrl":"10.1016/j.jpaa.2025.108097","url":null,"abstract":"<div><div>The rank <em>ρ</em> of the Néron-Severi group of a complex torus <em>X</em> of dimension <em>g</em> satisfies <span><math><mn>0</mn><mo>≤</mo><mi>ρ</mi><mo>≤</mo><msup><mrow><mi>g</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>=</mo><msup><mrow><mi>h</mi></mrow><mrow><mn>1</mn><mo>,</mo><mn>1</mn></mrow></msup></math></span>. The degree <span><math><mi>d</mi></math></span> of the extension field generated over <span><math><mi>Q</mi></math></span> by the entries of a period matrix of <em>X</em> imposes constraints on its Picard number <em>ρ</em> and, consequently, on the structure of <em>X</em>. In this paper, we show that when <span><math><mi>d</mi></math></span> is 2, 3, or 4, the Picard number <em>ρ</em> is necessarily large. Moreover, for an abelian variety <em>X</em> of dimension <em>g</em> with <span><math><mi>d</mi><mo>=</mo><mn>3</mn></math></span>, we establish a structure-type result: <em>X</em> must be isogenous to <span><math><msup><mrow><mi>E</mi></mrow><mrow><mi>g</mi></mrow></msup></math></span>, where <em>E</em> is an elliptic curve without complex multiplication. In this case, the Picard number satisfies <span><math><mi>ρ</mi><mo>(</mo><mi>X</mi><mo>)</mo><mo>=</mo><mfrac><mrow><mi>g</mi><mo>(</mo><mi>g</mi><mo>+</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>2</mn></mrow></mfrac></math></span>. As a byproduct, we obtain that if <span><math><mi>d</mi></math></span> is odd, then <span><math><mi>ρ</mi><mo>(</mo><mi>X</mi><mo>)</mo><mo>≤</mo><mfrac><mrow><mi>g</mi><mo>(</mo><mi>g</mi><mo>+</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>2</mn></mrow></mfrac></math></span>.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108097"},"PeriodicalIF":0.8,"publicationDate":"2025-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145159547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-17DOI: 10.1016/j.jpaa.2025.108095
Adriano De Santana , Rene Baltazar , Robson Vinciguerra , Wilian De Araujo
This paper investigates the isotropy groups of derivations on the Quantum Plane , defined by the relation , where , with . The main goal is to determine the automorphisms of the Quantum Plane that commutes with a fixed derivation δ. We describe conditions under which the isotropy group is trivial, finite, or infinite, depending on the structure of δ and whether q is a root of unity: additionally, we present the structure of the group in the finite case. A key tool is the analysis of polynomial equations of the form , arising from monomials in the inner part of δ. We also make explicit which finite subgroups of are isotropy groups of some derivation: either q root of unity or not. Techniques from algebraic geometry, such as intersection multiplicity, are also employed in the classification of the finite case.
{"title":"On isotropy groups of quantum plane","authors":"Adriano De Santana , Rene Baltazar , Robson Vinciguerra , Wilian De Araujo","doi":"10.1016/j.jpaa.2025.108095","DOIUrl":"10.1016/j.jpaa.2025.108095","url":null,"abstract":"<div><div>This paper investigates the isotropy groups of derivations on the Quantum Plane <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>q</mi></mrow></msub><mo>[</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>]</mo></math></span>, defined by the relation <span><math><mi>y</mi><mi>x</mi><mo>=</mo><mi>q</mi><mi>x</mi><mi>y</mi></math></span>, where <span><math><mi>q</mi><mo>∈</mo><msup><mrow><mi>k</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math></span>, with <span><math><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>≠</mo><mn>1</mn></math></span>. The main goal is to determine the automorphisms of the Quantum Plane that commutes with a fixed derivation <em>δ</em>. We describe conditions under which the isotropy group <span><math><msub><mrow><mtext>Aut</mtext></mrow><mrow><mi>δ</mi></mrow></msub><mo>(</mo><mi>A</mi><mo>)</mo></math></span> is trivial, finite, or infinite, depending on the structure of <em>δ</em> and whether <em>q</em> is a root of unity: additionally, we present the structure of the group in the finite case. A key tool is the analysis of polynomial equations of the form <span><math><msubsup><mrow><mi>μ</mi></mrow><mrow><mn>1</mn></mrow><mrow><mi>a</mi></mrow></msubsup><msubsup><mrow><mi>μ</mi></mrow><mrow><mn>2</mn></mrow><mrow><mi>b</mi></mrow></msubsup><mo>=</mo><mn>1</mn></math></span>, arising from monomials in the inner part of <em>δ</em>. We also make explicit which finite subgroups of <span><math><mi>Aut</mi><mo>(</mo><msub><mrow><mi>k</mi></mrow><mrow><mi>q</mi></mrow></msub><mo>[</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>]</mo><mo>)</mo></math></span> are isotropy groups of some derivation: either <em>q</em> root of unity or not. Techniques from algebraic geometry, such as intersection multiplicity, are also employed in the classification of the finite case.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108095"},"PeriodicalIF":0.8,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145109500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-15DOI: 10.1016/j.jpaa.2025.108094
Shripad M. Garge , Deep H. Makadiya
Let R be a commutative ring with unity. Consider the twisted Chevalley group of type Φ over R and its elementary subgroup . This paper investigates the normalizers of and in the larger group , where S is an extension ring of R. We establish that under certain conditions on R these normalizers coincide. Moreover, in the case of adjoint type groups, we show that they are precisely equal to .
{"title":"Normalizer of twisted Chevalley groups over commutative rings","authors":"Shripad M. Garge , Deep H. Makadiya","doi":"10.1016/j.jpaa.2025.108094","DOIUrl":"10.1016/j.jpaa.2025.108094","url":null,"abstract":"<div><div>Let <em>R</em> be a commutative ring with unity. Consider the twisted Chevalley group <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>π</mi><mo>,</mo><mi>σ</mi></mrow></msub><mo>(</mo><mi>Φ</mi><mo>,</mo><mi>R</mi><mo>)</mo></math></span> of type Φ over <em>R</em> and its elementary subgroup <span><math><msubsup><mrow><mi>E</mi></mrow><mrow><mi>π</mi><mo>,</mo><mi>σ</mi></mrow><mrow><mo>′</mo></mrow></msubsup><mo>(</mo><mi>Φ</mi><mo>,</mo><mi>R</mi><mo>)</mo></math></span>. This paper investigates the normalizers of <span><math><msubsup><mrow><mi>E</mi></mrow><mrow><mi>π</mi><mo>,</mo><mi>σ</mi></mrow><mrow><mo>′</mo></mrow></msubsup><mo>(</mo><mi>Φ</mi><mo>,</mo><mi>R</mi><mo>)</mo></math></span> and <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>π</mi><mo>,</mo><mi>σ</mi></mrow></msub><mo>(</mo><mi>Φ</mi><mo>,</mo><mi>R</mi><mo>)</mo></math></span> in the larger group <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>π</mi><mo>,</mo><mi>σ</mi></mrow></msub><mo>(</mo><mi>Φ</mi><mo>,</mo><mi>S</mi><mo>)</mo></math></span>, where <em>S</em> is an extension ring of <em>R</em>. We establish that under certain conditions on <em>R</em> these normalizers coincide. Moreover, in the case of adjoint type groups, we show that they are precisely equal to <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>π</mi><mo>,</mo><mi>σ</mi></mrow></msub><mo>(</mo><mi>Φ</mi><mo>,</mo><mi>R</mi><mo>)</mo></math></span>.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108094"},"PeriodicalIF":0.8,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145109501","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-12DOI: 10.1016/j.jpaa.2025.108088
Edwin J. Beggs, James E. Blake
We construct a Leray-Serre spectral sequence for fibre bundles for de Rham sheaf cohomology on noncommutative algebras. The morphisms are bimodules with zero-curvature extendable bimodule connections. This generalises definitions involving differentiable algebra maps to differentiable completely positive maps by using the KSGNS construction and Hilbert -bimodules with bimodule connections. We give examples of noncommutative fibre bundles, involving group algebras, matrix algebras, and the quantum torus.
在非交换代数上构造了de Rham轴上同调的纤维束的Leray-Serre谱序列。态射是具有零曲率可扩展双模连接的双模。利用KSGNS构造和具有双模连接的Hilbert C - C -双模,将涉及可微代数映射的定义推广到可微的完全正映射。我们给出了非交换纤维束的例子,涉及群代数、矩阵代数和量子环面。
{"title":"Noncommutative fibre bundles via bimodules","authors":"Edwin J. Beggs, James E. Blake","doi":"10.1016/j.jpaa.2025.108088","DOIUrl":"10.1016/j.jpaa.2025.108088","url":null,"abstract":"<div><div>We construct a Leray-Serre spectral sequence for fibre bundles for de Rham sheaf cohomology on noncommutative algebras. The morphisms are bimodules with zero-curvature extendable bimodule connections. This generalises definitions involving differentiable algebra maps to differentiable completely positive maps by using the KSGNS construction and Hilbert <span><math><msup><mrow><mi>C</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math></span>-bimodules with bimodule connections. We give examples of noncommutative fibre bundles, involving group algebras, matrix algebras, and the quantum torus.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108088"},"PeriodicalIF":0.8,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-11DOI: 10.1016/j.jpaa.2025.108089
Thomas Michael Keller , Gavin Pettigrew , Saskia Solotko , Lixin Zheng
For a finite group G, the vertices of the prime graph are the primes that divide , and two vertices p and q are adjacent if and only if there is an element of order pq in G. Prime graphs of solvable groups as well as groups whose noncyclic composition factors have order divisible by exactly three distinct primes have been classified in graph-theoretic terms. In this paper, we begin to develop a general theory on the existence of edges in the prime graph of an arbitrary T-solvable group, that is, a group whose composition factors are cyclic or isomorphic to a fixed nonabelian simple group T. We then apply these results to classify the prime graphs of T-solvable groups for, in a suitable sense, most T such that has exactly four prime divisors. We find that these groups almost always have a 3-colorable prime graph complement containing few possible triangles.
{"title":"Classifying prime graphs of finite groups – a methodical approach","authors":"Thomas Michael Keller , Gavin Pettigrew , Saskia Solotko , Lixin Zheng","doi":"10.1016/j.jpaa.2025.108089","DOIUrl":"10.1016/j.jpaa.2025.108089","url":null,"abstract":"<div><div>For a finite group <em>G</em>, the vertices of the prime graph <span><math><mi>Γ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> are the primes that divide <span><math><mo>|</mo><mi>G</mi><mo>|</mo></math></span>, and two vertices <em>p</em> and <em>q</em> are adjacent if and only if there is an element of order <em>pq</em> in <em>G</em>. Prime graphs of solvable groups as well as groups whose noncyclic composition factors have order divisible by exactly three distinct primes have been classified in graph-theoretic terms. In this paper, we begin to develop a general theory on the existence of edges in the prime graph of an arbitrary <em>T</em>-solvable group, that is, a group whose composition factors are cyclic or isomorphic to a fixed nonabelian simple group <em>T</em>. We then apply these results to classify the prime graphs of <em>T</em>-solvable groups for, in a suitable sense, most <em>T</em> such that <span><math><mo>|</mo><mi>T</mi><mo>|</mo></math></span> has exactly four prime divisors. We find that these groups almost always have a 3-colorable prime graph complement containing few possible triangles.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108089"},"PeriodicalIF":0.8,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-10DOI: 10.1016/j.jpaa.2025.108090
Jun Hu , Huansheng Li , Shuo Li
In this paper, we use the cyclotomic Mackey decomposition and branching rules of the seminormal bases of the semisimple cyclotomic Hecke algebras of type to give a new approach to computing the Schur element of for each ℓ-partition . Our formulae give a simple recursive relation between the Schur element and the Schur element of , where . We give our main results for both the non-degenerate and the degenerate cyclotomic Hecke algebras of type . The formulae of the Schur element that we derived are different superficially from all the known formulae in the literature.
{"title":"New formulae for the Schur elements of the cyclotomic Hecke algebra of type G(ℓ,1,n)","authors":"Jun Hu , Huansheng Li , Shuo Li","doi":"10.1016/j.jpaa.2025.108090","DOIUrl":"10.1016/j.jpaa.2025.108090","url":null,"abstract":"<div><div>In this paper, we use the cyclotomic Mackey decomposition and branching rules of the seminormal bases of the semisimple cyclotomic Hecke algebras of type <span><math><mi>G</mi><mo>(</mo><mi>ℓ</mi><mo>,</mo><mn>1</mn><mo>,</mo><mi>n</mi><mo>)</mo></math></span> to give a new approach to computing the Schur element <span><math><msub><mrow><mi>s</mi></mrow><mrow><mi>λ</mi></mrow></msub></math></span> of <span><math><msub><mrow><mi>H</mi></mrow><mrow><mi>ℓ</mi><mo>,</mo><mi>n</mi></mrow></msub></math></span> for each <em>ℓ</em>-partition <span><math><mi>λ</mi><mo>∈</mo><msub><mrow><mi>P</mi></mrow><mrow><mi>ℓ</mi><mo>,</mo><mi>n</mi></mrow></msub></math></span>. Our formulae give a simple recursive relation between the Schur element <span><math><msub><mrow><mi>s</mi></mrow><mrow><mi>λ</mi></mrow></msub></math></span> and the Schur element <span><math><msub><mrow><mi>s</mi></mrow><mrow><msub><mrow><mi>λ</mi></mrow><mrow><mo>↓</mo><mo>≤</mo><mo>(</mo><mi>n</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow></msub></mrow></msub></math></span> of <span><math><msub><mrow><mi>H</mi></mrow><mrow><mi>ℓ</mi><mo>,</mo><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msub></math></span>, where <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mo>↓</mo><mo>≤</mo><mo>(</mo><mi>n</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow></msub><mo>:</mo><mo>=</mo><mi>Shape</mi><mo>(</mo><msub><mrow><mo>(</mo><msup><mrow><mi>t</mi></mrow><mrow><mi>λ</mi></mrow></msup><mo>)</mo></mrow><mrow><mo>↓</mo><mo>≤</mo><mo>(</mo><mi>n</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow></msub><mo>)</mo></math></span>. We give our main results for both the non-degenerate and the degenerate cyclotomic Hecke algebras of type <span><math><mi>G</mi><mo>(</mo><mi>ℓ</mi><mo>,</mo><mn>1</mn><mo>,</mo><mi>n</mi><mo>)</mo></math></span>. The formulae of the Schur element that we derived are different superficially from all the known formulae in the literature.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108090"},"PeriodicalIF":0.8,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145061192","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}