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arXiv 1802.01742math.AG
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环面作用、局部化和上同调的诱导表示

Torus actions, localization and induced representations on cohomology

James B Carrell

摘要:

本文从环面作用的观点出发,研究了具有极大环面$T$的半单复线性代数群$G$的Weyl群$W=N_G(T)/T$在$G$的旗簇中的任意Springer簇的上同调代数上的Springer作用.继续工作[CK],给出了一个充分条件的一组$\mathcal{W}$作用在一个代数环面行动$(S,X)$上的不动点集的复射影品种$X$提升到表示的$\mathcal{W}$上的上同调代数$H^*(X)$(在$\mathbb{C}$),我们描述时的表示$H^*(X)$是等价的表示$\mathcal{W}$上的上同调$H^*(X^S)$的不动点集。作为这个定理的结果,我们给出了一个简单的证明,在$A$型的Alvis-Lusztig-Treumann定理,它描述了施普林格的代表$W$的施普林格品种对应于幂零李$(G)$的Levi子代数。在最后两节中,我们描述了特殊环面作用$(S,X)$的矩图$\mathfrak{M}(X)$的局部结构,并证明了如果有限群$\mathcal{W}$作用在$X$的矩图上,则$\mathcal{W}$诱导出$H^*(X)$上的作用对,即Knutson [Knu]和Tymoczko [Tym]的左右或点星作用对.特别地,对于包含$T$的$G$中的任何抛物线$P$,$W$作用于$(T,G/P)$的矩(或Bruhat)图$\mathfrak{M}(G/P)$,并且$W$对$H^*(G/P)$的右作用是诱导表示。进一步证明了$W$在$H^*(G/P)$上的左作用是平凡的.

英文摘要:

This note is motivated by the problem of understanding Springer's remarkable action of the Weyl group $W=N_G(T)/T$ of a semi-simple complex linear algebraic group $G$, with maximal torus $T$, on the cohomology algebra of an arbitrary Springer variety in the flag variety of $G$ from the viewpoint of torus actions. Continuing the work [CK] which gave a sufficient condition for a group $\mathcal{W}$ acting on the fixed point set of an algebraic torus action $(S,X)$ on a complex projective variety $X$ to lift to a representation of $\mathcal{W}$ on the cohomology algebra $H^*(X)$ (over $\mathbb{C}$), we describe when the representation on $H^*(X)$ is equivalent to the representation of $\mathcal{W}$ on the cohomology $H^*(X^S)$ of the fixed point set. As a consequence of this theorem, we give a simple proof in type $A$ of the Alvis-Lusztig-Treumann Theorem, which describes Springer's representation of $W$ for Springer varieties corresponding to nilpotents in a Levi subalgebra of Lie$(G)$. In the final two sections, we describe the local structure of the moment graph $\mathfrak{M}(X)$ of a special torus action $(S,X)$, and we also show that if a finite group $\mathcal{W}$ acts on the moment graph of $X$, then $\mathcal{W}$ induces pair of actions on $H^*(X)$, namely the left and right or dot and star actions of Knutson [Knu] and Tymoczko [Tym] respectively. In particular, $W$ acts on the moment (or Bruhat) graph $\mathfrak{M}(G/P)$ of $(T,G/P)$ for any parabolic $P$ in $G$ containing $T$, and the right action of $W$ on $H^*(G/P)$ is an induced representation. Furthermore, we show the left action of $W$ on $H^*(G/P)$ is trivial.

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