On Flat Flag-Transitive c.c *-Geometries

We study flat flag-transitive c.c ^*-geometries. We prove that, apart from one exception related to Sym(6), all these geometries are gluings in the meaning of [6]. They are obtained by gluing two copies of an affine space over GF(2). There are several ways of gluing two copies of the n-dimensional affine space over GF(2). In one way, which deserves to be called the canonical one, we get a geometry with automorphism group G = 2²ⁿ · L _n(2) and covered by the truncated Coxeter complex of type D ₂ ⁿ . The non-canonical ways give us geometries with smaller automorphism group (G ≤ 2²ⁿ · (2 ^n?1)n) and which seldom (never ?) can be obtained as quotients of truncated Coxeter complexes.     

More on Geometries of the Fischer Group Fi 22

We give a new, purely combinatorial characterization of geometries with diagram identifying each under some natural conditions—but not assuming any group action a priori—with one of the two geometries and related to the Fischer 3-transposition group Fi ₂₂ and its non-split central extension 3 · Fi ₂₂, respectively. As a by-product we improve the known characterization of the c-extended dual polar spaces for Fi ₂₂ and 3 · Fi ₂₂ and of the truncation of the c-extended 6-dimensional unitary polar space.     

Geometries of the Group PSL(2,11)

We determine all residually weakly primitive flag-transitive geometries for the groups PSL(2,11) and PGL(2,11). For the first of these we prove the existence by simple constructions while uniqueness, namely the fact that the lists are complete, relies on MAGMA programs. A central role is played by the subgroups Alt(5) in PSL(2,11). The highest rank of a geometry in our lists is four. Our work is related to various atlases of coset geometries.     

三角几何的基本群(英)

利用Building理论获得一种计算某些三角几何的基本群的新的方法．这种方法能够容易地计算出无限多有限三角几何的基拓扑基本群．     

LG/CY Correspondence Between tt* Geometries

The concept of $tt^∗$ geometric structure was introduced by physicists (see [4, 10] and references therein), and then studied firstly in mathematics by C. Hertling [28]. It is believed that the $tt^∗$ geometric structure contains the whole genus 0 information of a two dimensional topological field theory. In this paper, we propose the LG/CY correspondence conjecture for $tt^∗$ geometry and obtain the following result. Let $f ∈ \mathbb{C}[z_0,...,z_{n+1}]$ be a nondegenerate homogeneous polynomial of degree $nThe concept of $tt^∗$ geometric structure was introduced by physicists (see [4, 10] and references therein), and then studied firstly in mathematics by C. Hertling [28]. It is believed that the $tt^∗$ geometric structure contains the whole genus 0 information of a two dimensional topological field theory. In this paper, we propose the LG/CY correspondence conjecture for $tt^∗$ geometry and obtain the following result. Let $f ∈ \mathbb{C}[z_0,...,z_{n+1}]$ be a nondegenerate homogeneous polynomial of degree $nThe concept of tt* geometric structure was introduced by physicists(see[4,9]and references therein),and then studied firstly in mathematics by C.Hertling[26].It is believed that the tt* geometric structure contains the whole genus 0 information of a two dimensional topological field theory.In this paper,we propose the LG/CY correspondence conjecture for tt* geome-try and obtain the following result.Let f ∈?[z0,…,zn+1]be a nondegenerate homogeneous polynomial of degree n+2,then it defines a Calabi-Yau model represented by a Calabi-Yau hypersurface Xf in(CP)n+1 or a Landau-Ginzburg model represented by a hypersurface singularity( ?n+2,f),both can be written as a tt* structure.We proved that there exists a tt* substructure on Landau-Ginzburg side,which should correspond to the tt* structure from variation of Hodge structures in Calabi-Yau side.We build the isomorphism of almost all structures in tt* geometries between these two models except the isomorphism between real structures.     

A Geometric Characterization of Fischer's Baby Monster

The sporadic simple group F ₂ known as Fischer's Baby Monster acts flag-transitively on a rank 5 P-geometry . P-geometries are geometries with string diagrams, all of whose nonempty edges except one are projective planes of order 2 and one terminal edge is the geometry of the Petersen graph. Let be a flag-transitive P-geometry of rank 5. Suppose that each proper residue of is isomorphic to the corresponding residue in . We show that in this case is isomorphic to . This result realizes a step in classification of the flag-transitive P-geometries and also plays an important role in the characterization of the Fischer–Griess Monster in terms of its 2-local parabolic geometry.     

A Family of Geometries Related to the Suzuki Tower

ABSTRACT

Michio Suzuki constructed a sequence of five simple groups G _i , with i = 0,…, 4, and five graphs Δ _i , with i = 0,…, 4, such that Δ _i appears as a subgraph of Δ _i+1 for i = 0,…, 3 and G _i is an automorphism group of Δ _i for i = 0,…, 4. The largest group G ₄ was a new sporadic group of order 448 345 497 600. It is now called the Suzuki group Suz. These groups and graphs form what Jacques Tits calls the Suzuki tower. In a previous work, we constructed a rank four geometry Γ(HJ) on which the Hall-Janko sporadic simple group acts flag-transitively and residually weakly primitively. In this article, we show that Γ(HJ) belongs to a family of five geometries in bijection with the Suzuki tower. The largest of them is a geometry of rank six, on which the Suzuki sporadic group acts flag-transitively and residually weakly primitively.     

一类用仿射几何构造的半对称图

图X是一个有限简单无向图,如果图X是正则的且边传递但非点传递,则称X是半对称图.主要利用仿射几何构造了一类2p~n阶连通p~4度的半对称图的无限族,其中p≥n≥11.     

On the Generation of Some Embeddable GF(2) Geometries

The generating rank is determined for several GF(2)-embeddable geometries and it is demonstrated that their generating and embedding ranks are equal. Specifically, we prove that each of the two generalized hexagons of order (2, 2) has generating rank 14, that the central involution geometry of the Hall-Janko sporadic group has generating rank 28, and that the dual polar space DU(6,2) has generating rank 22. We also include a survey of all instances in which either the generating or embedding rank of an embeddable GF(2) geometry is known.     

A (c. L*-Geometry for the Sporadic Group J2

We prove the existence of a rank three geometry admitting the Hall–Janko group J2 as flag-transitive automorphism group and Aut(J2) as full automorphism group. This geometry belongs to the diagram (c·L*) and its nontrivial residues are complete graphs of size 10 and dual Hermitian unitals of order 3.     

Classification of Some Optimal Ternary Linear Codes of Small Length

A classification is given of some optimal ternary linear codes of small length. Dimension 2 is classified for every minimum distance. Dimension 3, 4 and 5 is classified up to minimum distance 12. For higher dimension a classification is given where possible.     

以$M_{11}$为基柱的旗传递点本原2-设计的完全分类

近年来,很多学者研究了以散在单群作为本原自同构群基柱的旗传递2-设计的一些分类工作.本文在此基础之上,给出了以散在单群$M_{11}$作为基柱的旗传递点本原2-设计的完全分类,得到了14个不同构的非平凡2-设计.     

Geometric Hyperplanes of Lie Incidence Geometries

A geometric hyperplane of a point--line geometry is a proper subspace which meets each line non-trivially. If H is a hyperplane of a projective space P, and the point line geometry has an embedding in P , then the pullback from H is a geometric hyperplane of . We show that all geometric hyperplanes arise in this way for polar spaces of typeD _n , the Grassmann space of lines, and the exceptional geometry E _1,6 . The actual geometric hyperplanes are studied in several cases.     

关于内7-闭单群的结构

研究内ｐ－闭群的结构是一个很活跃的课题．对于ｐ＝２，３，５的内ｐ－闭群的结构已经被确定（见［１，２，３］）．本文确定内７－闭单群的结构     

最高阶元素个数为40的非可解群的分类

设$\varphi$为群${\rm Aut}(N)$的同态,记$H_\varphi\times N$为群$N$借助于群$H$的半直积.设$G$为有限不可解群,本文证明: 若$G$中最高阶元素个数为40, 则$G$同构于下列群之一:(1)~$Z_{4\varphi}\times A_5$,\,${\rm ker}\varphi=Z_2$; (2)~$D_{8\varphi}\times A_5,\,{\rm ker}\varphi=Z_2\times Z_2$; (3)~$G/N=S_5$, $N=Z(G)=Z_2$; (4)~$G/N=S_5$, $N=Z_2\times Z_2,\,N\cap Z(G)=Z_2$.     

The Classification of Primitive Sharp Permutation Groups of Type {0, k}

The purpose in this paper is to complete the classification of primitive sharp permutation groups of type ({0, k}, n) by proving that no such group can be almost simple.     

On the stability of equivariant foliations

We prove an equivariant version of the Reeb-Thurston stability theorem for foliations invariant under an action of a discrete group.