Almost isotropy-maximal manifolds of non-negative curvature

Abstract

We extend the equivariant classification results of Escher and Searle for closed, simply connected, Riemannian n n -manifolds with non-negative sectional curvature admitting isometric isotropy-maximal torus actions to the class of such manifolds admitting isometric strictly almost isotropy-maximal torus actions. In particular, we prove that any such manifold is equivariantly diffeomorphic to the free, linear quotient by a torus of a product of spheres of dimensions greater than or equal to three.