On convexity and the Iwasawa decomposition of split real and complex Kac-Moody groups

Paul Zellhofer; Ralf Köhl

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arXiv · 2312.02584

On convexity and the Iwasawa decomposition of split real and complex Kac-Moody groups

Paul Zellhofer·Ralf Köhl

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Abstract

We prove an analogue of Kostant's convexity theorem for split real and complex Kac-Moody groups associated to free and cofree root data. The result can be seen as a first step towards describing the multiplication map in a Kac-Moody group in terms of Iwasawa coordinates. Our method involves a detailed analysis of the geometry of Weyl group orbits in the Cartan subalgebra of a real Kac-Moody algebra. It provides an alternative proof of Kostant convexity for semisimple Lie groups and also generalizes a linear analogue of Kostant's theorem for Kac-Moody algebras that has been established by Kac and Peterson in 1984.

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Paul Zellhofer, Ralf Köhl. 2023-12-05. On convexity and the Iwasawa decomposition of split real and complex Kac-Moody groups. https://arxiv.org/abs/2312.02584

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