Cosmological models in semi-classical and higher order gravitational theories

We have studied semiclassical models with a classical scalar field, givingexact solutions in the cases of a ⁴ and an exponentialself-interaction potential, in the last case we have also studied theinfluence of the vacuum polarization terms on the stability of the power-lawsolutions. We have also found cosmological exact solutions to the higherorder gravitational equations derived from a Lagrangian with a R ^k Rstructure, and investigated the stability of the de Sitter and Minkowskispace-time in the sixth order approximation of this theory.