Homology, Homotopy and Applications

Volume 20 (2018)

Number 1

A comparison of two models of orbispaces

Pages: 329 – 358

DOI: https://dx.doi.org/10.4310/HHA.2018.v20.n1.a19


Alexander Körschgen (Mathematisches Institut der Universität Bonn, Germany)


This paper proves that the two homotopy theories for orbispaces given by Gepner and Henriques and by Schwede, respectively, agree by providing a zig-zag of Dwyer–Kan equivalences between the respective topologically enriched index categories. The aforementioned authors establish various models for unstable global homotopy theory with compact Lie group isotropy, and orbispaces serve as a common denominator for their particular approaches. Although the two flavors of orbispaces are expected to agree with each other, a concrete comparison zig-zag has not been known so far. We bridge this gap by providing such a zig-zag which asserts that all those models for unstable global homotopy theory with compact Lie group isotropy which have been described by the authors named above agree with each other.

On our way, we provide a result which is of independent interest. For a large class of free actions of a compact Lie group, we prove that the homotopy quotient by the group action is weakly equivalent to the strict quotient. This is a known result under more restrictive conditions, e.g., for free actions on a manifold. We broadly extend these results to all free actions of a compact Lie group on a compactly generated Hausdorff space.


orbispace, unstable global homotopy theory, compact Lie group, homotopy quotient

2010 Mathematics Subject Classification

Primary 55R91. Secondary 18D20.

The author was supported in part by a grant from the International Max Planck Research School on Moduli Spaces.

Received 1 June 2017

Received revised 29 October 2017

Published 28 February 2018