Abstract. We study certain cross-effects of the unstable homotopy of spheres. These cross-effects were constructed by Weiss, for different purposes, in the context of "Orthogonal calculus". We show that Mithchell's finite spectra with A kfree cohomology (constructed in [Mt85]) arise naturally as stabilizations of Weiss' cross-effects. In particular, we find that after a suitable Bousfield localization, our cross-effects, which capture meaningful information about the unstable homotopy of spheres, are homotopy equivalent to the infinite loop spaces associated with Mitchell's spectra. This last result is a partial generalization of the main result of Mahowald and the author in [AM97].
IntroductionLet X be a topological space. We are interested in studying the difference between the homotopy type of X and that of S 2 X, the double suspension of X (for technical reasons the statements turn out to be a little cleaner if one works with double suspensions rather than single suspensions). One naive way to compare X and S 2 X would be by means of the map X → S 2 X given by taking the smash product of the identity map on X with the inclusion S 0 → S 2 . Of course, this map is null-homotopic and thus is unlikely to provide useful information about the difference between X and S 2 X. A much better idea is to consider the Freudental (double) suspension map w 1 : X → Ω 2 S 2 X. Let F 1 (X) be the homotopy fiber of this map. We regard F 1 (X) as measuring the difference between the homotopy type of X and that of S 2 X. We would like to iterate the process and find higher analogues of the suspension map and higher iterated differences of the suspension map. Thus at the second stage we would like to find a suitable way to compare F 1 (X) with F 1 (S 2 X). Obviously, there exists a natural map F 1 (X) → Ω 2 F 1 (S 2 X). However, this map turns out to be null-homotopic, just as the map X → S 2 X is null-homotopic. It follows from the 1991 Mathematics Subject Classification. 55P40, 55P42, 55P65.