Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0002
Matthias Beck, Danai Deligeorgaki, Max Hlavacek, Jerónimo Valencia-Porras
The Ehrhart polynomial ehrP(n) of a lattice polytope P counts the number of integer points in the n-th dilate of P. The f*-vector of P, introduced by Felix Breuer in 2012, is the vector of coefficients of ehrP(n) with respect to the binomial coefficient basis $begin{array}{} bigl{binom{n-1}{0},binom{n-1}{1},dots,binom{n-1}{d}bigr}, end{array}$ where d = dim P. Similarly to h/h*-vectors, the f*-vector of P coincides with the f-vector of its unimodular triangulations (if they exist). We present several inequalities that hold among the coefficients of f*-vectors of lattice polytopes. These inequalities resemble striking similarities with existing inequalities for the coefficients of f-vectors of simplicial polytopes; e.g., the first half of the f*-coefficients increases and the last quarter decreases. Even though f*-vectors of polytopes are not always unimodal, there are several families of polytopes that carry the unimodality property. We also show that for any polytope with a given Ehrhart h*-vector, there is a polytope with the same h*-vector whose f*-vector is unimodal.
由 Felix Breuer 于 2012 年提出的 P 的 f * 向量是 ehr P (n) 关于二项式系数基础 $begin{array}{} 的系数向量。与 h/h *-向量类似,P 的 f *-向量与其单模态三角剖分(如果存在的话)的 f -向量重合。我们提出了格状多面体的 f *-向量系数之间的几个不等式。这些不等式与简单多面体 f *-向量系数的现有不等式有惊人的相似之处;例如,f *-系数的前半部分会增加,而后四分之一会减少。尽管多面体的 f *-vectors 并不总是单峰的,但有几个多面体族具有单峰特性。我们还证明,对于任何具有给定艾尔哈特 h *向量的多面体,都有一个具有相同 h *向量的多面体,其 f *向量是单峰的。
{"title":"Inequalities for f *-vectors of lattice polytopes","authors":"Matthias Beck, Danai Deligeorgaki, Max Hlavacek, Jerónimo Valencia-Porras","doi":"10.1515/advgeom-2024-0002","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0002","url":null,"abstract":"The Ehrhart polynomial ehr<jats:sub> <jats:italic>P</jats:italic> </jats:sub>(<jats:italic>n</jats:italic>) of a lattice polytope <jats:italic>P</jats:italic> counts the number of integer points in the <jats:italic>n</jats:italic>-th dilate of <jats:italic>P</jats:italic>. The <jats:italic>f</jats:italic> <jats:sup>*</jats:sup>-vector of <jats:italic>P</jats:italic>, introduced by Felix Breuer in 2012, is the vector of coefficients of ehr<jats:sub> <jats:italic>P</jats:italic> </jats:sub>(<jats:italic>n</jats:italic>) with respect to the binomial coefficient basis <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" xlink:href=\"graphic/j_advgeom-2024-0002_eq_001.png\"/> <jats:tex-math>$begin{array}{} bigl{binom{n-1}{0},binom{n-1}{1},dots,binom{n-1}{d}bigr}, end{array}$</jats:tex-math> </jats:alternatives> </jats:inline-formula> where <jats:italic>d</jats:italic> = dim <jats:italic>P</jats:italic>. Similarly to <jats:italic>h/h</jats:italic> <jats:sup>*</jats:sup>-vectors, the <jats:italic>f</jats:italic> <jats:sup>*</jats:sup>-vector of <jats:italic>P</jats:italic> coincides with the <jats:italic>f</jats:italic>-vector of its unimodular triangulations (if they exist). We present several inequalities that hold among the coefficients of <jats:italic>f</jats:italic> <jats:sup>*</jats:sup>-vectors of lattice polytopes. These inequalities resemble striking similarities with existing inequalities for the coefficients of <jats:italic>f</jats:italic>-vectors of simplicial polytopes; e.g., the first half of the <jats:italic>f</jats:italic> <jats:sup>*</jats:sup>-coefficients increases and the last quarter decreases. Even though <jats:italic>f</jats:italic> <jats:sup>*</jats:sup>-vectors of polytopes are not always unimodal, there are several families of polytopes that carry the unimodality property. We also show that for any polytope with a given Ehrhart <jats:italic>h</jats:italic> <jats:sup>*</jats:sup>-vector, there is a polytope with the same <jats:italic>h</jats:italic> <jats:sup>*</jats:sup>-vector whose <jats:italic>f</jats:italic> <jats:sup>*</jats:sup>-vector is unimodal.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"9 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222019","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2023-0027
Ciro Ciliberto, Claudio Fontanari
We present two applications of Hao’s proof of the Weak Bounded Negativity Conjecture. First, we address the so-called Weighted Bounded Negativity Conjecture and we prove that all but finitely many reduced and irreducible curves C on the blow-up of ℙ2 at n points satisfy the inequality $begin{array}{} displaystyle C^2 ge min bigl{-frac{1}{12} n (C.L +27), -2 bigr}, end{array}$ where L is the pull-back of a line. Next, we turn to the widely open conjecture that the canonical degree C.KX of an integral curve on a smooth projective surface X is bounded from above by an expression of the form A(g − 1) + B, where g is the geometric genus of C and A, B are constants depending only on X. We prove that this conjecture holds with A = − 1 under the assumptions h0(X, −KX) = 0 and h0(X, 2KX + C) = 0.
我们介绍了郝氏对弱有界否定猜想证明的两个应用。首先,我们讨论了所谓的加权有界否定猜想,并证明了在ℙ2的炸开上,除了有限多的还原曲线和不可还原曲线C之外,所有在n个点上的还原曲线和不可还原曲线C都满足不等式 $begin{array}{}displaystyle C^2 ge min bigl{-frac{1}{12} n (C.L +27), -2 bigr}, end{array}$ 其中 L 是直线的回拉。接下来,我们将讨论一个广为流传的猜想,即光滑投影面 X 上积分曲线的规范度 C.KX 是由 A(g - 1) + B 形式的表达式从上而下限定的,其中 g 是 C 的几何属,A、B 是仅取决于 X 的常数。
{"title":"Variations on the Weak Bounded Negativity Conjecture","authors":"Ciro Ciliberto, Claudio Fontanari","doi":"10.1515/advgeom-2023-0027","DOIUrl":"https://doi.org/10.1515/advgeom-2023-0027","url":null,"abstract":"We present two applications of Hao’s proof of the <jats:italic>Weak Bounded Negativity Conjecture</jats:italic>. First, we address the so-called <jats:italic>Weighted Bounded Negativity Conjecture</jats:italic> and we prove that all but finitely many reduced and irreducible curves <jats:italic>C</jats:italic> on the blow-up of ℙ<jats:sup>2</jats:sup> at <jats:italic>n</jats:italic> points satisfy the inequality <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" xlink:href=\"graphic/j_advgeom-2023-0027_eq_001.png\"/> <jats:tex-math>$begin{array}{} displaystyle C^2 ge min bigl{-frac{1}{12} n (C.L +27), -2 bigr}, end{array}$</jats:tex-math> </jats:alternatives> </jats:inline-formula> where <jats:italic>L</jats:italic> is the pull-back of a line. Next, we turn to the widely open conjecture that the canonical degree <jats:italic>C</jats:italic>.<jats:italic>K<jats:sub>X</jats:sub> </jats:italic> of an integral curve on a smooth projective surface <jats:italic>X</jats:italic> is bounded from above by an expression of the form <jats:italic>A</jats:italic>(<jats:italic>g</jats:italic> − 1) + <jats:italic>B</jats:italic>, where <jats:italic>g</jats:italic> is the geometric genus of <jats:italic>C</jats:italic> and <jats:italic>A</jats:italic>, <jats:italic>B</jats:italic> are constants depending only on <jats:italic>X</jats:italic>. We prove that this conjecture holds with <jats:italic>A</jats:italic> = − 1 under the assumptions <jats:italic>h</jats:italic> <jats:sup>0</jats:sup>(<jats:italic>X</jats:italic>, −<jats:italic>K<jats:sub>X</jats:sub> </jats:italic>) = 0 and <jats:italic>h</jats:italic> <jats:sup>0</jats:sup>(<jats:italic>X</jats:italic>, 2<jats:italic>K<jats:sub>X</jats:sub> </jats:italic> + <jats:italic>C</jats:italic>) = 0.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"183 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222020","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0004
Georgios Kydonakis, Hao Sun, Lutian Zhao
We demonstrate the construction of Poisson structures via Lie algebroids on moduli spaces of twisted stable Higgs bundles over stacky curves. The construction provides new examples of Poisson structures on such moduli spaces. Special attention is paid to moduli spaces of parabolic Higgs bundles over a root stack.
{"title":"Poisson Structures on moduli spaces of Higgs bundles over stacky curves","authors":"Georgios Kydonakis, Hao Sun, Lutian Zhao","doi":"10.1515/advgeom-2024-0004","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0004","url":null,"abstract":"We demonstrate the construction of Poisson structures via Lie algebroids on moduli spaces of twisted stable Higgs bundles over stacky curves. The construction provides new examples of Poisson structures on such moduli spaces. Special attention is paid to moduli spaces of parabolic Higgs bundles over a root stack.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"9 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222017","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0003
Yonggyu Lee, Fu Liu
For a ∈ $begin{array}{} displaystyle mathbb{R}_{geq 0}^{n} end{array}$, the Tesler polytope Tesn( a ) is the set of upper triangular matrices with non-negative entries whose hook sum vector is a . We first give a different proof of the known fact that for every fixed a 0 ∈ $begin{array}{} displaystyle mathbb{R}_{ gt 0}^{n} end{array}$, all the Tesler polytopes Tesn( a ) are deformations of Tesn( a 0). We then calculate the deformation cone of Tesn( a 0). In the process, we also show that any deformation of Tesn( a 0) is a translation of a Tesler polytope. Lastly, we consider a larger family of polytopes called flow polytopes which contains the family of Tesler polytopes and chracterize the flow polytopes which are deformations of Tesn( a 0).
For a ∈ $begin{array}{}displaystyle mathbb{R}_{geq 0}^{n}end{array}$ ,Tesler 多面体 Tes n ( a ) 是具有非负条目的上三角矩阵的集合,其钩和向量是 a 。 我们首先给出一个不同的证明,即对于每一个固定的 a 0 ∈ $begin{array}{} 的已知事实。displaystyle mathbb{R}_{ gt 0}^{n}end{array}$ ,所有的 Tesler 多面体 Tes n ( a ) 都是 Tes n ( a 0) 的变形。然后我们计算 Tes n ( a 0) 的变形锥。在此过程中,我们还证明了 Tes n ( a 0) 的任何变形都是 Tesler 多面体的平移。最后,我们考虑了一个更大的多面体族,称为流多面体,它包含了 Tesler 多面体族,并对作为 Tes n ( a 0) 变形的流多面体进行了分析。
{"title":"Deformation cones of Tesler polytopes","authors":"Yonggyu Lee, Fu Liu","doi":"10.1515/advgeom-2024-0003","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0003","url":null,"abstract":"For <jats:italic> a </jats:italic> ∈ <jats:inline-formula> <jats:alternatives> <jats:tex-math>$begin{array}{} displaystyle mathbb{R}_{geq 0}^{n} end{array}$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, the Tesler polytope Tes<jats:sub> <jats:italic>n</jats:italic> </jats:sub>(<jats:italic> a </jats:italic>) is the set of upper triangular matrices with non-negative entries whose hook sum vector is <jats:italic> a </jats:italic>. We first give a different proof of the known fact that for every fixed <jats:italic> a </jats:italic> <jats:sub>0</jats:sub> ∈ <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" xlink:href=\"graphic/j_advgeom-2024-0003_eq_002.png\"/> <jats:tex-math>$begin{array}{} displaystyle mathbb{R}_{ gt 0}^{n} end{array}$</jats:tex-math> </jats:alternatives> </jats:inline-formula>, all the Tesler polytopes Tes<jats:sub> <jats:italic>n</jats:italic> </jats:sub>(<jats:italic> a </jats:italic>) are deformations of Tes<jats:sub> <jats:italic>n</jats:italic> </jats:sub>(<jats:italic> a </jats:italic> <jats:sub>0</jats:sub>). We then calculate the deformation cone of Tes<jats:sub> <jats:italic>n</jats:italic> </jats:sub>(<jats:italic> a </jats:italic> <jats:sub>0</jats:sub>). In the process, we also show that any deformation of Tes<jats:sub> <jats:italic>n</jats:italic> </jats:sub>(<jats:italic> a </jats:italic> <jats:sub>0</jats:sub>) is a translation of a Tesler polytope. Lastly, we consider a larger family of polytopes called flow polytopes which contains the family of Tesler polytopes and chracterize the flow polytopes which are deformations of Tes<jats:sub> <jats:italic>n</jats:italic> </jats:sub>(<jats:italic> a </jats:italic> <jats:sub>0</jats:sub>).","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"6 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222021","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0008
Sergey I. Agafonov, Thaís G. P. Alves
We prove that if the geodesic flow on a surface has an integral which is fractional-linear in momenta, then the dimension of the space of such integrals is either 3 or 5, the latter case corresponding to constant gaussian curvature. We give also a geometric criterion for the existence of fractional-linear integrals: such an integral exists if and only if the surface carries a geodesic 4-web with constant cross-ratio of the four directions tangent to the web leaves.
{"title":"Fractional-linear integrals of geodesic flows on surfaces and Nakai’s geodesic 4-webs","authors":"Sergey I. Agafonov, Thaís G. P. Alves","doi":"10.1515/advgeom-2024-0008","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0008","url":null,"abstract":"We prove that if the geodesic flow on a surface has an integral which is fractional-linear in momenta, then the dimension of the space of such integrals is either 3 or 5, the latter case corresponding to constant gaussian curvature. We give also a geometric criterion for the existence of fractional-linear integrals: such an integral exists if and only if the surface carries a geodesic 4-web with constant cross-ratio of the four directions tangent to the web leaves.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"42 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222018","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0006
Yiming Li, Yanlu Lian, Miao Fu, Yuqin Zhang
Based on Zong’s work [26] on translative packing densities of 3-dimensional convex bodies, we present a local method to estimate the density θt(C3) of the densest translative covering of an octahedron. As a consequence we prove that θt(C3) ≥ 1 + 6.6 × 10–8, which is the first non-trivial lower bound for this density.
{"title":"Lower bound on the translative covering density of octahedra","authors":"Yiming Li, Yanlu Lian, Miao Fu, Yuqin Zhang","doi":"10.1515/advgeom-2024-0006","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0006","url":null,"abstract":"Based on Zong’s work [26] on translative packing densities of 3-dimensional convex bodies, we present a local method to estimate the density <jats:italic>θ<jats:sup>t</jats:sup> </jats:italic>(<jats:italic>C</jats:italic> <jats:sub>3</jats:sub>) of the densest translative covering of an octahedron. As a consequence we prove that <jats:italic>θ<jats:sup>t</jats:sup> </jats:italic>(<jats:italic>C</jats:italic> <jats:sub>3</jats:sub>) ≥ 1 + 6.6 × 10<jats:sup>–8</jats:sup>, which is the first non-trivial lower bound for this density.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"286 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222015","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0007
M. Angeles Alfonseca, M. Cordier, J. Jerónimo-Castro, E. Morales-Amaya
Let n ≥ 3 and let K ⊂ ℝn be a convex body. A point p ∈ int K is said to be a Larman point of K if for every hyperplane Π passing through p, the section Π ∩ K has an (n – 2)-plane of symmetry. If p is a Larman point of K and for every section Π ∩ K, p is in the corresponding (n – 2)-plane of symmetry, then we call p a revolution point of K. We conjecture that if K contains a Larman point which is not a revolution point, then K is either an ellipsoid or a body of revolution. This generalizes a conjecture of Bezdek for n = 3. We prove several results related to the conjecture for strictly convex origin symmetric bodies. Namely, if K ⊂ ℝn is a strictly convex origin symmetric body that contains a revolution point p which is not the origin, then K is a body of revolution. This generalizes the False Axis of Revolution Theorem in [7]. We also show that if p is a Larman point of K ⊂ ℝ3 and there exists a line L such that p ∉ L and, for every plane Π passing through p, the line of symmetry of the section Π ∩ K intersects L, then K is a body of revolution (in some cases, K is a sphere). We obtain a similar result for projections of K. Additionally, for K ⊂ ℝn with n ≥ 4, we show that if every hyperplane section or projection of K is a body of revolution and K has a unique diameter D, then K is a body of revolution with axis D.
设 n ≥ 3,且 K ⊂ ℝ n 是一个凸体。如果经过 p 的每一个超平面 Π 的截面 Π ∩ K 都有一个 (n - 2) 对称面,则称点 p∈ int K 为 K 的拉曼点。如果 p 是 K 的一个拉曼点,并且对于每一段 Π ∩ K,p 都在相应的(n - 2)对称面上,那么我们称 p 为 K 的一个旋转点。我们猜想,如果 K 包含一个不是旋转点的拉曼点,那么 K 要么是一个椭圆体,要么是一个旋转体。这概括了贝兹德克对 n = 3 的猜想。我们证明了与严格凸原点对称体猜想相关的几个结果。也就是说,如果 K ⊂ ℝ n 是一个严格凸原点对称体,其中包含一个非原点的旋转点 p,那么 K 是一个旋转体。这概括了 [7] 中的假旋转轴定理。我们还证明,如果 p 是 K ⊂ ℝ3 的一个拉曼点,并且存在一条直线 L,使得 p ∉ L,并且对于经过 p 的每一个平面 Π,截面 Π ∩ K 的对称线都与 L 相交,那么 K 是一个旋转体(在某些情况下,K 是一个球体)。此外,对于 K ⊂ ℝ n(n≥4),我们证明了如果 K 的每个超平面截面或投影都是一个旋转体,并且 K 有唯一的直径 D,那么 K 是一个以 D 为轴的旋转体。
{"title":"Characterization of the sphere and of bodies of revolution by means of Larman points","authors":"M. Angeles Alfonseca, M. Cordier, J. Jerónimo-Castro, E. Morales-Amaya","doi":"10.1515/advgeom-2024-0007","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0007","url":null,"abstract":"Let <jats:italic>n</jats:italic> ≥ 3 and let <jats:italic>K</jats:italic> ⊂ ℝ<jats:sup> <jats:italic>n</jats:italic> </jats:sup> be a convex body. A point <jats:italic>p</jats:italic> ∈ int <jats:italic>K</jats:italic> is said to be a <jats:italic>Larman point</jats:italic> of <jats:italic>K</jats:italic> if for every hyperplane <jats:italic>Π</jats:italic> passing through <jats:italic>p</jats:italic>, the section <jats:italic>Π</jats:italic> ∩ <jats:italic>K</jats:italic> has an (<jats:italic>n</jats:italic> – 2)-plane of symmetry. If <jats:italic>p</jats:italic> is a Larman point of <jats:italic>K</jats:italic> and for every section <jats:italic>Π</jats:italic> ∩ <jats:italic>K</jats:italic>, <jats:italic>p</jats:italic> is in the corresponding (<jats:italic>n</jats:italic> – 2)-plane of symmetry, then we call <jats:italic>p</jats:italic> a <jats:italic>revolution</jats:italic> point of <jats:italic>K</jats:italic>. We conjecture that if <jats:italic>K</jats:italic> contains a Larman point which is not a revolution point, then <jats:italic>K</jats:italic> is either an ellipsoid or a body of revolution. This generalizes a conjecture of Bezdek for <jats:italic>n</jats:italic> = 3. We prove several results related to the conjecture for strictly convex origin symmetric bodies. Namely, if <jats:italic>K</jats:italic> ⊂ ℝ<jats:sup> <jats:italic>n</jats:italic> </jats:sup> is a strictly convex origin symmetric body that contains a revolution point <jats:italic>p</jats:italic> which is not the origin, then <jats:italic>K</jats:italic> is a body of revolution. This generalizes the False Axis of Revolution Theorem in [7]. We also show that if <jats:italic>p</jats:italic> is a Larman point of <jats:italic>K</jats:italic> ⊂ ℝ<jats:sup>3</jats:sup> and there exists a line <jats:italic>L</jats:italic> such that <jats:italic>p</jats:italic> ∉ <jats:italic>L</jats:italic> and, for every plane <jats:italic>Π</jats:italic> passing through <jats:italic>p</jats:italic>, the line of symmetry of the section <jats:italic>Π</jats:italic> ∩ <jats:italic>K</jats:italic> intersects <jats:italic>L</jats:italic>, then <jats:italic>K</jats:italic> is a body of revolution (in some cases, <jats:italic>K</jats:italic> is a sphere). We obtain a similar result for projections of <jats:italic>K</jats:italic>. Additionally, for <jats:italic>K</jats:italic> ⊂ ℝ<jats:sup> <jats:italic>n</jats:italic> </jats:sup> with <jats:italic>n</jats:italic> ≥ 4, we show that if every hyperplane section or projection of <jats:italic>K</jats:italic> is a body of revolution and <jats:italic>K</jats:italic> has a unique diameter <jats:italic>D</jats:italic>, then <jats:italic>K</jats:italic> is a body of revolution with axis <jats:italic>D</jats:italic>.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"109 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222022","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0005
Alice Garbagnati, Yulieth Prieto-Montañez
A Shioda–Inose structure is a geometric construction which associates to an Abelian surface a projective K3 surface in such a way that their transcendental lattices are isometric. This geometric construction was described by Morrison by considering special symplectic involutions on the K3 surfaces. After Morrison several authors provided explicit examples. The aim of this paper is to generalize Morrison’s results and some of the known examples to an analogous geometric construction involving not involutions, but order 3 automorphisms. Therefore, we define generalized Shioda–Inose structures of order 3, we identify the K3 surfaces and the Abelian surfaces which appear in these structures and we provide explicit examples.
{"title":"Generalized Shioda–Inose structures of order 3","authors":"Alice Garbagnati, Yulieth Prieto-Montañez","doi":"10.1515/advgeom-2024-0005","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0005","url":null,"abstract":"A Shioda–Inose structure is a geometric construction which associates to an Abelian surface a projective K3 surface in such a way that their transcendental lattices are isometric. This geometric construction was described by Morrison by considering special symplectic involutions on the K3 surfaces. After Morrison several authors provided explicit examples. The aim of this paper is to generalize Morrison’s results and some of the known examples to an analogous geometric construction involving not involutions, but order 3 automorphisms. Therefore, we define generalized Shioda–Inose structures of order 3, we identify the K3 surfaces and the Abelian surfaces which appear in these structures and we provide explicit examples.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"6 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222042","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0001
S.G. Barwick, W.-A. Jackson, P. Wild
In this article we look at the geometric structure of the feet of an orthogonal Buekenhout–Metz unital 𝓤 in PG(2, q2). We show that the feet of each point form a set of type (0, 1, 2, 4). Further, we discuss the structure of any 4-secants, and determine exactly when the feet form an arc.
{"title":"The feet of orthogonal Buekenhout–Metz unitals","authors":"S.G. Barwick, W.-A. Jackson, P. Wild","doi":"10.1515/advgeom-2024-0001","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0001","url":null,"abstract":"In this article we look at the geometric structure of the feet of an orthogonal Buekenhout–Metz unital 𝓤 in PG(2, <jats:italic>q</jats:italic> <jats:sup>2</jats:sup>). We show that the feet of each point form a set of type (0, 1, 2, 4). Further, we discuss the structure of any 4-secants, and determine exactly when the feet form an arc.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"286 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222041","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}
Pub Date : 2024-08-13DOI: 10.1515/advgeom-2024-0009
Christopher Lin
On a 7-manifold with a G2-structure, we study conformal symmetries — which are vector fields whose flow generate conformal transformations of the G2-structure. In particular, we focus on compact 7-manifolds and the condition that the Lee form of the G2-structure is closed. Among other observations, we show that conformal symmetries are determined within a conformal class of the G2-structure by the symmetries of a unique (up to homothety) G2-structure whose Lee form is harmonic. On a related note, we also demonstrate that symmetries are split along fibrations when the Lee vector field is itself a symmetry.
在具有 G 2 结构的 7-manifold 上,我们研究共形对称性--即其流动产生 G 2 结构共形变换的向量场。我们尤其关注紧凑的 7-manifolds,以及 G 2-结构的李形式是封闭的这一条件。除其他观察结果外,我们还证明了共形对称性是在 G 2-结构的共形类中由唯一(同性)G 2-结构的对称性决定的,而该结构的李形式是谐波的。与此相关,我们还证明了当李向量场本身是一个对称性时,对称性会沿着纤维分裂。
{"title":"Some observations on conformal symmetries of G 2-structures","authors":"Christopher Lin","doi":"10.1515/advgeom-2024-0009","DOIUrl":"https://doi.org/10.1515/advgeom-2024-0009","url":null,"abstract":"On a 7-manifold with a <jats:italic>G</jats:italic> <jats:sub>2</jats:sub>-structure, we study conformal symmetries — which are vector fields whose flow generate conformal transformations of the <jats:italic>G</jats:italic> <jats:sub>2</jats:sub>-structure. In particular, we focus on compact 7-manifolds and the condition that the Lee form of the <jats:italic>G</jats:italic> <jats:sub>2</jats:sub>-structure is closed. Among other observations, we show that conformal symmetries are determined within a conformal class of the <jats:italic>G</jats:italic> <jats:sub>2</jats:sub>-structure by the symmetries of a unique (up to homothety) <jats:italic>G</jats:italic> <jats:sub>2</jats:sub>-structure whose Lee form is harmonic. On a related note, we also demonstrate that symmetries are split along fibrations when the Lee vector field is itself a symmetry.","PeriodicalId":7335,"journal":{"name":"Advances in Geometry","volume":"6 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222016","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}