## Nonpositively curved manifolds of higher rank.(English)Zbl 0585.53031

The author investigates the structure of the universal covering space $$\tilde M$$ of a complete Riemannian manifold M with nonpositive sectional curvature bounded from below by some constant $$-a^ 2$$. The rank of a unit tangent vector v of M is defined to be the dimension of the space of parallel Jacobi vector fields along the geodesic $$\gamma_ v$$ with the initial velocity v. Further, the rank of the Riemannian manifold M is defined as $rank(M)=\min \{rank(v)| \quad v\in SM\}.$ The main theorem says that if M has finite volume, then $$\tilde M$$ is a space of rank one, or a symmetric space, or a product of such spaces. Corollary: Suppoe that M has finite volume. If M is irreducible and $$rank(M)=k\geq 2$$, then M is a locally symmetric space of noncompact type of rank k.
Reviewer: O.Kowalski

### MSC:

 53C20 Global Riemannian geometry, including pinching
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