Totally Geodesic Foliations and Doubly Ruled Surfaces in a Compact Lie Group

TL;DR

This paper investigates the geometry of totally geodesic foliations and doubly ruled surfaces in compact Lie groups, providing new rigidity theorems and examples that advance the classification of Riemannian submersions.

Contribution

It introduces the concept of doubly ruled parameterized surfaces, extends their study beyond Riemannian submersions, and establishes foundational rigidity results in compact Lie groups.

Findings

Holonomy group acts transitively on fibers in simple compact Lie groups.

Doubly ruled surfaces are characterized by specific geometric properties.

Several rigidity theorems and unexpected examples are provided.

Abstract

For a Riemannian submersion from a simple compact Lie group with a bi-invariant metric, we prove the action of its holonomy group on the fibers is transitive. As a step towards classifying Riemannian submersions with totally geodesic fibers, we consider the parameterized surface induced by lifting a base geodesic to points along a geodesic in a fiber. Such a surface is "doubly ruled" (it is ruled by horizontal geodesics and also by vertical geodesics). Its characterizing properties allow us to define "doubly ruled parameterized surfaces" in any Riemannian manifold, independent of Riemannian submersions. We initiate a study of the doubly ruled parameterized surfaces in compact Lie groups and in other symmetric spaces by establishing several rigidity theorems and by providing several examples with unexpected properties.