Horizontal diameter of unit spheres with polar foliations and infinitesimally polar actions

For a singular Riemannian foliation [Formula: see text] on a Riemannian manifold, a curve is called horizontal if it meets the leaves of [Formula: see text] perpendicularly. For a singular Riemannian foliation [Formula: see text] on a unit sphere [Formula: see text], we show that if [Formula: see text] is a polar foliation or if [Formula: see text] is given by the orbits of an infinitesimally polar action, then the horizontal diameter of [Formula: see text] is [Formula: see text], i.e. any two points in [Formula: see text] can be connected by a horizontal curve of length [Formula: see text].

POLAR ACTIONS ON BERGER SPHERES

The object of this article is to study a torus action on a so-called Berger sphere. We also make some comments on polar actions on naturally reductive homogeneous spaces. Finally, we prove a rigidity-type theorem for Riemannian manifolds carrying a polar action with a fix point.