Large Scale Geometry of 4-dimensional Closed Nonpositively Curved Real   Analytic Manifolds
  We study the asymptotic cones of the universal covering spaces of closed 4-dimensional nonpositively curved real analytic manifolds. We show that the existence of nonstandard components in the Tits boundary, discovered by Christoph Hummel and Victor Schroeder, depends only on the quasi-isometry type of the fundamental group. 
Mohamad A. Hindawi