Hostname: page-component-7b7567c8c-2n9c9 Total loading time: 0 Render date: 2026-11-14T20:07:29.453Z Has data issue: false hasContentIssue false

Springer's Weyl Group Representation via Localization

Published online by Cambridge University Press:  20 November 2018

Jim Carrell
Affiliation:
Department of Mathematics, University of British Columbia, Vancouver, B.C.. e-mail: carrell@math.ubc.ca
Kiumars Kaveh
Affiliation:
Department of Mathematics, University of Pittsburgh, Pittsburgh, PA, USA. e-mail: kaveh@pitt.edu
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the 'Save PDF' action button.

Let $G$ denote a reductive algebraic group over $\mathbb{C}$ and $x$ a nilpotent element of its Lie algebra $\mathfrak{g}$ . The Springer variety ${{B}_{x}}$ is the closed subvariety of the flag variety $B$ of $G$ parameterizing the Borel subalgebras of $\mathfrak{g}$ containing $x$ . It has the remarkable property that the Weyl group $W$ of $G$ admits a representation on the cohomology of ${{B}_{x}}$ even though $W$ rarely acts on ${{B}_{x}}$ itself. Well-known constructions of this action due to Springer and others use technical machinery from algebraic geometry. The purpose of this note is to describe an elementary approach that gives this action when $x$ is what we call parabolic-surjective. The idea is to use localization to construct an action of $W$ on the equivariant cohomology algebra $H_{s}^{*}({{B}_{x}})$ , where $S$ is a certain algebraic subtorus of $G$ . This action descends to ${{H}^{*}}({{B}_{x}})$ via the forgetful map and gives the desired representation. The parabolic-surjective case includes all nilpotents of type $A$ and, more generally, all nilpotents for which it is known that $W$ acts on $H_{s}^{*}({{B}_{x}})$ for some torus $S$ . Our result is deduced from a general theorem describing when a group action on the cohomology of the ûxed point set of a torus action on a space lifts to the full cohomology algebra of the space.

Information

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 2017