Local and global homogeneity for three obstinate spheres

Abstract

In this note we complete a study of globally homogeneous Riemannian quotients Γ\\(M,ds2) in positive curvature. Specifically, M is a homogeneous space G/H that admits a G–invariant Riemannian metric of strictly positive sectional curvature, and ds2 is a G–invariant Riemannian metric on M, not necessarily normal and not necessarily positively curved. The Homogeneity Conjecture is that Γ\\(M,ds2) is (globally) homogeneous if and only if (M,ds2) is homogeneous and every γ∈Γ is of constant displacement on (M,ds2). In an earlier paper we verified that conjecture for all homogeneous spaces that admit an invariant Riemannian metric of positive curvature — with three exceptions, all of them odd dimensional spheres, which surprisingly did not yield to the earlier approaches. In this note we deal with those exceptions: we develop some methods that let us verify the Homogeneity Conjecture for those three obstinate spheres. That completes verification of the Homogeneity Conjecture in positive curvature.