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ISSN (electronic): 1364-0380
ISSN (print): 1465-3060
Automorphisms of $p$–compact groups and their root data

Kasper K S Andersen and Jesper Grodal

Geometry & Topology 12 (2008) 1427–1460

We construct a model for the space of automorphisms of a connected p–compact group in terms of the space of automorphisms of its maximal torus normalizer and its root datum. As a consequence we show that any homomorphism to the outer automorphism group of a p–compact group can be lifted to a group action, analogous to a classical theorem of de Siebenthal for compact Lie groups. The model of this paper is used in a crucial way in our paper ‘The classification of 2-compact groups’ [arXiv:math.AT/0611437], where we prove the conjectured classification of 2–compact groups and determine their automorphism spaces.

$p$-compact group, root datum, maximal torus normalizer
Mathematical Subject Classification 2000
Primary: 55R35
Secondary: 20G99, 22E15, 55P35
Received: 11 January 2007
Revised: 1 April 2008
Accepted: 30 November 2007
Published: 10 June 2008
Proposed: Haynes Miller
Seconded: Paul Goerss, Ralph Cohen
Kasper K S Andersen
Department of Mathematical Sciences
University of Aarhus
DK-8000 Aarhus C
Jesper Grodal
Department of Mathematical Sciences
University of Copenhagen
DK-2100 Copenhagen