Relativistic cosmology models

In this thesis classical relativistic cosmology models based on the Robertson-Walker metric are studied. Einstein field equations and scalar fields equations are taken into account together, as grand unifield theories and superstring theories that unify gravity with other interactions predict the existence of cosmic scalar fields. Due to the non-linearity of the Einstein field equations and their functional structure, the number of degrees of the freedom is infinite. That is why toy models having lower degrees of freedom and higher symmetry are chosen for this study in flat space-time (k=0). The calculations of a cosmological model with one scaler field (Dereli et al 1993,1994) are continued and the existence of four different solutions is shown. Only one of these solutions is physically acceptable. In the same way the calculations for two scalar fields are carried out and the conditions to be satisfied for the existence of solutions are derived