  We study chaotic inflation driven by a real, massive, homogeneous minimally
coupled scalar field in a flat Robertson-Walker spacetime. The semiclassical
limit for gravity is considered, whereas the scalar field is treated quantum
mechanically by the technique of invariants in order to also investigate the
dynamics of the system for non-classical states of the latter. An inflationary
stage is found to be possible for a large set of initial quantum states,
obviously including the coherent ones. States associated with a vanishing mean
value of the field (such as the vacuum and the thermal) can also lead to
inflation, however for such states we cannot make a definitive prediction due
to the importance of higher order corrections during inflation. The results for
the above coupled system are described and their corrections evaluated
perturbatively.
