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Kostant convexity for affine buildings

  • Petra Hitzelberger
Published/Copyright: February 12, 2010
Forum Mathematicum
From the journal Volume 22 Issue 5

Abstract

We prove an analogue of Kostant's convexity theorem for thick affine buildings and give an application for groups with affine BN-pairs. Recall that there are two natural retractions of the affine building onto a fixed apartment A: The retraction r centered at an alcove in A and the retraction ρ centered at a chamber in the spherical building at infinity. We prove that for each special vertex xA the set ρ(r–1(W .x)) is a certain convex hull of W .x. The proof can be reduced to a statement about Coxeter complexes and heavily relies on a character formula for highest weight representations of algebraic groups.

Received: 2008-03-12
Revised: 2009-03-02
Published Online: 2010-02-12
Published in Print: 2010-September

© de Gruyter 2010

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