Equivariant formality of corank-one isotropy actions and products of rational spheres

Abstract

We completely characterize the pairs of connected Lie groups $G > K$ such that $\mathrm{rank}(G) - \mathrm{rank}(K) = 1$ and the left action of $K$ on $G/K$ is equivariantly formal. The analysis requires us to correct and extend an existing partial classification of homogeneous quotients $G/K$ with the rational homotopy type of a product of an odd- and an even-dimensional sphere.