On the de Rham cohomology of solvmanifolds

Using results by D.Witte [35] on the superigidity of lattices in solvable Lie groups we get a new proof of a recent remarkable result obtained by D. Guan [15] on the de Rham cohomology of a compact solvmanifold, i.e., of a quotient of a connected and simply connected solvable Lie group G by a lattice \Gamma. This result can be applied to compute the Betti numbers of a compact solvmanifold G/\Gamma even in the case that the solvable Lie group G and the lattice \Gamma do not satisfy the Mostow condition.