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The loops on U(n)/O(n) and U(2n)/Sp(n)

Published online by Cambridge University Press:  24 October 2008

M. C. Crabb  and
S. A. Mitchell
M. C. Crabb
Affiliation:
Department of Mathematics, University of Washington, Seattle, U.S.A.
S. A. Mitchell
Affiliation:
Department of Mathematics, University of Washington, Seattle, U.S.A.
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Extract

In [6] and [9] the second author and Bill Richter showed that the natural ‘degree’ filtration on the homology of ΩSU(n) has a geometric realization, and that this filtration stably splits (as conjectured by M. Hopkins and M. Mahowald). The purpose of the present paper is to prove the real and quaternionic analogues of these results. To explain what this means, consider the following two ways of viewing the filtration and splitting for ΩSU(n). When n = ∞, ΩSU = BU. The filtration is BU(1)⊆BU(2)⊆… and the splitting BU≅ V1≤<∞is a theorem of Snaith[14]. The result for ΩSU(n) may then be viewed as a ‘restriction’ of the result for BU. On the other hand there is a well-known inclusion ℂPn−1. This extends to a map ΩΣℂPn−1→ΩSU(n), and the filtration (or splitting) may be viewed, at least algebraically, as a ‘quotient’ of the James filtration (or splitting) of ΩΣℂPn−1. It is now clear what is meant by the ‘real and quaternionic analogues’. In the quaternionic case, we replace BU by BSp=Ω(SU/SP), ΩSU(n) by Ω(SU(2n)/SP(n))and ℂPn−1 by ℍPn−1. The integral homology of Ω(SU(2n)/SP(n)) is the symmetric algebra on the homology of ℍPn−1, and may be filtered by the various symmetric powers. We show that this filtration can be realized geometrically, and that the spaces of the filtration are certain (singular) real algebraic varieties (exactly as in the complex case). The strata of the filtration are vector bundles over filtrations of Ω(SU(2n−2)/SP(n−1)), and the filtration stably splits. See Theorems (1·7) and (2·1) for the precise statement. In the real case we replace BU by Ω(SU/SO), Ω(SU(n)/SO(n)) and ℂPn−1 by ℝPn−1. Here integral homology must be replaced by mod 2 homology, and splitting is only obtained after localization at 2. (Snaith's splitting of BO in [14] can be refined [2, 8] so as to be exactly analogous to the splitting of BU:BO≅V1≤<∞MO(k).)

Type
Research Article
Information
Mathematical Proceedings of the Cambridge Philosophical Society , Volume 104 , Issue 1 , July 1988 , pp. 95 - 103
Copyright
Copyright © Cambridge Philosophical Society 1988

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References

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