  We develop a new structural result for cohomogeneity one actions on (not
necessarily irreducible) symmetric spaces of noncompact type and arbitrary
rank. We apply this result to classify cohomogeneity one actions on
SL(n,R)/SO(n), n>1, up to orbit equivalence. We also reduce the classification
problem on a reducible space to the classification on each one of its
irreducible factors, which in particular allows to classify cohomogeneity one
actions on any finite product of hyperbolic spaces.

Differential Geometry