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Veronesean embeddings of dual polar spaces of orthogonal type

机译:Veronesean嵌入正交型的双极性空间

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摘要

Given a point-line geometry $\Gamma$ and a pappian projective space $\cal S$, a veronesean embedding of $\Gamma$ in $\cal S$ is an injective map $e$ from the point-set of $\Gamma$ to the set of points of $\cal S$ mapping the lines of $\Gamma$ onto non-singular conics of $\cal S$ and such that $e(\Gamma)$ spans $\cal S$. In this paper we study veronesean embeddings of the dual polar space $\Delta_n$ associated to a non-singular quadratic form $q$ of Witt index $n \geq 2$ in $V = V(2n+1,\mathbb{F})$. Three such embeddings are considered, namely the Grassmann embedding $\varepsilon^{\mathrm{gr}}_n$ which maps a maximal singular subspace $\langle v_1,..., v_n\rangle$ of $V$ (namely a point of $\Delta_n$) to the point $\langle \wedge_{i=1}^nv_i\rangle$ of $\mathrm{PG}(\bigwedge^nV)$, the composition $\varepsilon^{\mathrm{vs}}_n := \nu_{2^n}\circ \varepsilon^{\mathrm{spin}}_n$ of the spin (projective) embedding $\varepsilon^{\mathrm{spin}}_n$ of $\Delta_n$ in $\mathrm{PG}(2^n-1,\mathbb{F})$ with the quadric veronesean map $\nu_{2^n}:V(2^n,\mathbb{F})\rightarrow V({{2^n+1}\choose 2}, \mathbb{F})$, and a third embedding $\tilde{\varepsilon}_n$ defined algebraically in the Weyl module $V(2\lambda_n)$, where $\lambda_n$ is the fundamental dominant weight associated to the $n$-th simple root of the root system of type $B_n$. We shall prove that $\tilde{\varepsilon}_n$ and $\varepsilon^{\mathrm{vs}}_n$ are isomorphic. If $\mathrm{char}(\F)\neq 2$ then $V(2\lambda_n)$ is irreducible and $\tilde{\varepsilon}_n$ is isomorphic to $\varepsilon^{\mathrm{gr}}_n$ while if $\mathrm{char}(\F)= 2$ then $\varepsilon^{\mathrm{gr}}_n$ is a proper quotient of $\tilde{\varepsilon}_n$. In this paper we shall study some of these submodules. Finally we turn to universality, focusing on the case of $n = 2$. We prove that if $\F$ is a finite field of odd order $q > 3$ then $\varepsilon^{\mathrm{sv}}_2$ is relatively universal. On the contrary, if $\mathrm{char}(\F)= 2$ then $\varepsilon^{\mathrm{vs}}_2$ is not universal. We also prove that if $\F$ is a perfect field of characteristic 2 then $\varepsilon^{\mathrm{vs}}_n$ is not universal, for any $n \geq 2$.
机译:给定点线几何$ \ Gamma $和pappian射影空间$ \ cal S $,将$ \ Gamma $嵌入到$ \ cal S $中的Veronesean嵌入是从$ \的点集中得到的射影图$ e $将Gamma $映射到$ \ cal S $的点集,将$ \ Gamma $的线映射到$ \ cal S $的非奇异圆锥形上,使得$ e(\ Gamma)$跨越$ \ cal S $。在本文中,我们研究了与Witt指数$ n \ geq 2 $的非奇异二次形式$ q $相关的双极空间$ \ Delta_n $的Veresanean嵌入,其中$ V = V(2(n + 1),\ mathbb {F })$。考虑了三个这样的嵌入,即格拉斯曼嵌入$ \ varepsilon ^ {\ mathrm {gr}} _ n $,该映射映射了最大奇异子空间$ \ langle v_1,...,v_n \ rangle $ $ V $(即一个点$ \ Delta_n $)到$ \ mathrm {PG}(\ bigwedge ^ nV)$$的点$ \ langle \ wedge_ {i = 1} ^ nv_i \ rangle $,组成$ \ varepsilon ^ {\ mathrm {vs }} _ n:= \ nu_ {2 ^ n} \ circ \ varepsilon ^ {\ mathrm {spin}} _ n $的旋转(投射)嵌入$ \ Delta_n的$ \ varepsilon ^ {\ mathrm {spin}} _ n $ $在$ \ mathrm {PG}(2 ^ n-1,\ mathbb {F})$中具有二次Veronesean映射$ \ nu_ {2 ^ n}:V(2 ^ n,\ mathbb {F})\ rightarrow V({{{2 ^ n + 1} \ choose 2},\ mathbb {F})$,以及在Weyl模块$ V(2 \ lambda_n)$中代数定义的第三个嵌入$ \ tilde {\ varepsilon} _n $ ,其中$ \ lambda_n $是与类型$ B_n $的根系统的第$ n $个简单根相关的基本主导权重。我们将证明$ \ tilde {\ varepsilon} _n $和$ \ varepsilon ^ {\ mathrm {vs}} _ n $是同构的。如果$ \ mathrm {char}(\ F)\ neq 2 $则$ V(2 \ lambda_n)$是不可约的,而$ \ tilde {\ varepsilon} _n $与$ \ varepsilon ^ {\ mathrm {gr}}同构_n $,而如果$ \ mathrm {char}(\ F)= 2 $,则$ \ varepsilon ^ {\ mathrm {gr}} _ n $是$ \ tilde {\ varepsilon} _n $的适当商。在本文中,我们将研究其中一些子模块。最后,我们转向普遍性,重点关注$ n = 2 $的情况。我们证明,如果$ \ F $是一个奇数阶$ q> 3 $的有限域,则$ \ varepsilon ^ {\ mathrm {sv}} _ 2 $是相对通用的。相反,如果$ \ mathrm {char}(\ F)= 2 $,则$ \ varepsilon ^ {\ mathrm {vs}} _ 2 $不是通用的。我们还证明,如果$ \ F $是特征2的理想场,则对于任何$ n \ geq 2 $,$ \ varepsilon ^ {\ mathrm {vs}} _ n $都不通用。

著录项

  • 作者

    Cardinali I.; Pasini A.;

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  • 年度 2013
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  • 原文格式 PDF
  • 正文语种 eng
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