Pub Date : 2025-10-10DOI: 10.1016/j.jpaa.2025.108108
Christopher A. Schroeder, Hung P. Tong-Viet
A recurring theme in finite group theory is understanding how the structure of a finite group is determined by the arithmetic properties of group invariants. There are results in the literature determining the structure of finite groups whose irreducible character degrees, conjugacy class sizes or indices of maximal subgroups are odd. These results have been extended to include those finite groups whose character degrees or conjugacy class sizes are not divisible by 4. In this paper, we determine the structure of finite groups whose maximal subgroups have index not divisible by 4. As an application, we obtain some new 2-nilpotency criteria.
{"title":"Finite groups all of whose maximal subgroups have almost odd index","authors":"Christopher A. Schroeder, Hung P. Tong-Viet","doi":"10.1016/j.jpaa.2025.108108","DOIUrl":"10.1016/j.jpaa.2025.108108","url":null,"abstract":"<div><div>A recurring theme in finite group theory is understanding how the structure of a finite group is determined by the arithmetic properties of group invariants. There are results in the literature determining the structure of finite groups whose irreducible character degrees, conjugacy class sizes or indices of maximal subgroups are odd. These results have been extended to include those finite groups whose character degrees or conjugacy class sizes are not divisible by 4. In this paper, we determine the structure of finite groups whose maximal subgroups have index not divisible by 4. As an application, we obtain some new 2-nilpotency criteria.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108108"},"PeriodicalIF":0.8,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145333348","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 : 2025-10-06DOI: 10.1016/j.jpaa.2025.108107
Suprajo Das , Saipriya Dubey , Sudeshna Roy , Jugal K. Verma
This article investigates the computational aspects of the ε-multiplicity. Primarily, we show that the ε-multiplicity of a homogeneous ideal I in a two-dimensional standard graded domain of finite type over an algebraically closed field of arbitrary characteristic, is always a rational number. In this situation, we produce a formula for the ε-multiplicity of I in terms of certain mixed multiplicities associated to I. In any dimension, under the assumptions that the saturated Rees algebra of I is finitely generated, we give a different expression of the ε-multiplicity in terms of mixed multiplicities by using the Veronese degree. This enabled us to make various explicit computations of ε-multiplicities. We further write a Macaulay2 algorithm to compute ε-multiplicity (under the Noetherian hypotheses) even when the base ring is not necessarily standard graded.
{"title":"Computing epsilon multiplicities in graded algebras","authors":"Suprajo Das , Saipriya Dubey , Sudeshna Roy , Jugal K. Verma","doi":"10.1016/j.jpaa.2025.108107","DOIUrl":"10.1016/j.jpaa.2025.108107","url":null,"abstract":"<div><div>This article investigates the computational aspects of the <em>ε</em>-multiplicity. Primarily, we show that the <em>ε</em>-multiplicity of a homogeneous ideal <em>I</em> in a two-dimensional standard graded domain of finite type over an algebraically closed field of arbitrary characteristic, is always a rational number. In this situation, we produce a formula for the <em>ε</em>-multiplicity of <em>I</em> in terms of certain mixed multiplicities associated to <em>I</em>. In any dimension, under the assumptions that the saturated Rees algebra of <em>I</em> is finitely generated, we give a different expression of the <em>ε</em>-multiplicity in terms of mixed multiplicities by using the Veronese degree. This enabled us to make various explicit computations of <em>ε</em>-multiplicities. We further write a Macaulay2 algorithm to compute <em>ε</em>-multiplicity (under the Noetherian hypotheses) even when the base ring is not necessarily standard graded.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108107"},"PeriodicalIF":0.8,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145268345","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 : 2025-10-01DOI: 10.1016/j.jpaa.2025.108105
Sophie Raynor
Circuit algebras are a symmetric analogue of Jones's planar algebras introduced to study finite-type invariants of virtual knotted objects. Circuit algebra structures appear, in different forms, across mathematics. This paper provides a dictionary for translating between their diverse incarnations and describing their wider context. A formal definition of a broad class of circuit algebras is established and three equivalent descriptions of circuit algebras are provided: in terms of operads of wiring diagrams, modular operads and categories of Brauer diagrams. As an application, circuit algebra characterisations of algebras over the orthogonal and symplectic groups are given.
{"title":"Functorial, operadic and modular operadic combinatorics of circuit algebras","authors":"Sophie Raynor","doi":"10.1016/j.jpaa.2025.108105","DOIUrl":"10.1016/j.jpaa.2025.108105","url":null,"abstract":"<div><div>Circuit algebras are a symmetric analogue of Jones's planar algebras introduced to study finite-type invariants of virtual knotted objects. Circuit algebra structures appear, in different forms, across mathematics. This paper provides a dictionary for translating between their diverse incarnations and describing their wider context. A formal definition of a broad class of circuit algebras is established and three equivalent descriptions of circuit algebras are provided: in terms of operads of wiring diagrams, modular operads and categories of Brauer diagrams. As an application, circuit algebra characterisations of algebras over the orthogonal and symplectic groups are given.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108105"},"PeriodicalIF":0.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145268346","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 : 2025-10-01DOI: 10.1016/j.jpaa.2025.108106
Lee Tae Young
We determine precisely which irreducible hypergeometric sheaves have an extraspecial normalizer in characteristic 2 as their geometric monodromy groups. This resolves the last open case of the classification of local monodromy at 0 of irreducible hypergeometric sheaves with finite geometric monodromy group.
{"title":"Hypergeometric sheaves and extraspecial groups in even characteristic","authors":"Lee Tae Young","doi":"10.1016/j.jpaa.2025.108106","DOIUrl":"10.1016/j.jpaa.2025.108106","url":null,"abstract":"<div><div>We determine precisely which irreducible hypergeometric sheaves have an extraspecial normalizer in characteristic 2 as their geometric monodromy groups. This resolves the last open case of the classification of local monodromy at 0 of irreducible hypergeometric sheaves with finite geometric monodromy group.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108106"},"PeriodicalIF":0.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222117","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 : 2025-10-01DOI: 10.1016/j.jpaa.2025.108102
Kiryong Chung , Jaehyun Kim , Jeong-Seop Kim
Let X be a Fano threefold of index one and degree 22 with . Such a threefold X can be realized as the zero locus of a regular section s of over the Grassmannian , where and is the universal subbundle. When the section s is given by the net of the -invariant skew-symmetric forms, we call it the Mukai-Umemura (MU) variety. In this paper, we prove that the Hilbert scheme of rational quartic curves in the MU-variety is smooth, and we compute its Poincaré polynomial by applying Białynicki-Birula's theorem.
{"title":"Rational quartic curves in the Mukai-Umemura variety","authors":"Kiryong Chung , Jaehyun Kim , Jeong-Seop Kim","doi":"10.1016/j.jpaa.2025.108102","DOIUrl":"10.1016/j.jpaa.2025.108102","url":null,"abstract":"<div><div>Let <em>X</em> be a Fano threefold of index one and degree 22 with <span><math><mrow><mi>Pic</mi></mrow><mo>(</mo><mi>X</mi><mo>)</mo><mo>≅</mo><mi>Z</mi></math></span>. Such a threefold <em>X</em> can be realized as the zero locus of a regular section <strong>s</strong> of <span><math><msup><mrow><mo>(</mo><msup><mrow><mo>⋀</mo></mrow><mrow><mn>2</mn></mrow></msup><msup><mrow><mi>U</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>)</mo></mrow><mrow><mo>⊕</mo><mn>3</mn></mrow></msup></math></span> over the Grassmannian <span><math><mrow><mi>Gr</mi></mrow><mo>(</mo><mn>3</mn><mo>,</mo><mi>V</mi><mo>)</mo></math></span>, where <span><math><mi>dim</mi><mo></mo><mi>V</mi><mo>=</mo><mn>7</mn></math></span> and <span><math><mi>U</mi></math></span> is the universal subbundle. When the section <strong>s</strong> is given by the net of the <span><math><msub><mrow><mi>SL</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>-invariant skew-symmetric forms, we call it the Mukai-Umemura (MU) variety. In this paper, we prove that the Hilbert scheme of rational quartic curves in the MU-variety is smooth, and we compute its Poincaré polynomial by applying Białynicki-Birula's theorem.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108102"},"PeriodicalIF":0.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222114","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 : 2025-10-01DOI: 10.1016/j.jpaa.2025.108104
Justin Fong , Mitsuhiro Miyazaki
The F-pure threshold is the characteristic p counter part of the log canonical threshold in characteristic zero. It is a numerical invariant associated to the singularities of a variety, hence computing its value is important. We give a closed formula for the F-pure threshold of the irrelevant maximal ideal of Schubert cycles, which are the homogeneous coordinate rings of Schubert subvarieties of a Grassmannian. The main point of the computation is to give an explicit formula for the a-invariant of a Schubert cycle. The derivation of both formulas is made possible through the combinatorics of the underlying poset of these rings.
f -纯阈值是特征0中对数正则阈值的特征p计数器部分。它是一个与各种奇点有关的数值不变量,因此计算它的值是很重要的。我们给出了无关极大理想Schubert环的f -纯阈值的一个封闭公式,Schubert环是一类Grassmannian的Schubert子变量的齐次坐标环。计算的重点是给出舒伯特循环的a不变量的显式公式。这两个公式的推导是通过对这些环的基本偏序集的组合而实现的。
{"title":"The F-pure threshold of a Schubert cycle","authors":"Justin Fong , Mitsuhiro Miyazaki","doi":"10.1016/j.jpaa.2025.108104","DOIUrl":"10.1016/j.jpaa.2025.108104","url":null,"abstract":"<div><div>The <em>F</em>-pure threshold is the characteristic <em>p</em> counter part of the log canonical threshold in characteristic zero. It is a numerical invariant associated to the singularities of a variety, hence computing its value is important. We give a closed formula for the <em>F</em>-pure threshold of the irrelevant maximal ideal of Schubert cycles, which are the homogeneous coordinate rings of Schubert subvarieties of a Grassmannian. The main point of the computation is to give an explicit formula for the <em>a</em>-invariant of a Schubert cycle. The derivation of both formulas is made possible through the combinatorics of the underlying poset of these rings.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108104"},"PeriodicalIF":0.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222116","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 : 2025-10-01DOI: 10.1016/j.jpaa.2025.108101
Elad Paran , Thieu N. Vo
We study Noether's normalization lemma for finitely generated algebras over a division algebra. In its classical form, the lemma states that if I is a proper ideal of the ring of polynomials over a field F, then the quotient ring is a finite extension of a polynomial ring over F. We prove that the lemma holds when is the ring of polynomials in n central variables over a division algebra D. We provide examples demonstrating that Noether's normalization may fail for the skew polynomial ring with respect to commuting automorphisms of D. We give a sufficient condition for under which the normalization lemma holds for such ring. In the case where is a field, this sufficient condition is proved to be necessary.
{"title":"Noether's normalization in skew polynomial rings","authors":"Elad Paran , Thieu N. Vo","doi":"10.1016/j.jpaa.2025.108101","DOIUrl":"10.1016/j.jpaa.2025.108101","url":null,"abstract":"<div><div>We study Noether's normalization lemma for finitely generated algebras over a division algebra. In its classical form, the lemma states that if <em>I</em> is a proper ideal of the ring <span><math><mi>R</mi><mo>=</mo><mi>F</mi><mo>[</mo><msub><mrow><mi>t</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>t</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>]</mo></math></span> of polynomials over a field <em>F</em>, then the quotient ring <span><math><mi>R</mi><mo>/</mo><mi>I</mi></math></span> is a finite extension of a polynomial ring over <em>F</em>. We prove that the lemma holds when <span><math><mi>R</mi><mo>=</mo><mi>D</mi><mo>[</mo><msub><mrow><mi>t</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>t</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>]</mo></math></span> is the ring of polynomials in <em>n</em> central variables over a division algebra <em>D</em>. We provide examples demonstrating that Noether's normalization may fail for the skew polynomial ring <span><math><mi>D</mi><mo>[</mo><msub><mrow><mi>t</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>t</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>;</mo><msub><mrow><mi>σ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>]</mo></math></span> with respect to commuting automorphisms <span><math><msub><mrow><mi>σ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> of <em>D</em>. We give a sufficient condition for <span><math><msub><mrow><mi>σ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> under which the normalization lemma holds for such ring. In the case where <span><math><mi>D</mi><mo>=</mo><mi>F</mi></math></span> is a field, this sufficient condition is proved to be necessary.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108101"},"PeriodicalIF":0.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145222115","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 : 2025-10-01DOI: 10.1016/j.jpaa.2025.108103
Natsume Kitagawa
Corti defined the notion of standard models of del Pezzo fibrations, and studied their existence over with a fixed generic fibre in [6]. In this paper, we prove the existence of standard models of del Pezzo fibrations of degree 4 in characteristic >2. To show this, we use the notion of Kollár stability, which was introduced in [12] and [1].
{"title":"On the standard models of del Pezzo fibrations of degree four","authors":"Natsume Kitagawa","doi":"10.1016/j.jpaa.2025.108103","DOIUrl":"10.1016/j.jpaa.2025.108103","url":null,"abstract":"<div><div>Corti defined the notion of standard models of del Pezzo fibrations, and studied their existence over <span><math><mi>C</mi></math></span> with a fixed generic fibre in <span><span>[6]</span></span>. In this paper, we prove the existence of standard models of del Pezzo fibrations of degree 4 in characteristic >2. To show this, we use the notion of Kollár stability, which was introduced in <span><span>[12]</span></span> and <span><span>[1]</span></span>.</div></div>","PeriodicalId":54770,"journal":{"name":"Journal of Pure and Applied Algebra","volume":"229 11","pages":"Article 108103"},"PeriodicalIF":0.8,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145333342","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 : 2025-09-29DOI: 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}