On single scalar field cosmology

Observations suggest, that there may be periods in the history of the universe, including the present one, in which its evolution is driven by scalar fields. This paper is concerned with the solution of the evolution equations for a spatially flat universe driven by a single scalar field. Some general theorems relevant to the cosmology of these models are presented, and several approaches to solve the equations are discussed. For some potentials special exact solutions can be found, and for the case of exponential potentials the complete solution is rederived in a new parametrization. For the general case solutions are constructed in terms of a power series expansion in the field. The issue of double-valuedness of such a series expansion in case of oscillating fields with turning points is addressed and resolved.