  We study a nonperturbative single field (inflaton) governed cosmological
model from a 5D Noncompact Kaluza-Klein (NKK) theory of gravity. The inflaton
field fluctuations are estimated for different epochs of the evolution of the
universe. We conclude that the inflaton field has been sliding down its
(quadratic) potential hill along all the evolution of the universe and a mass
of the order of the Hubble parameter. In the model here developed the only free
parameter is the Hubble parameter, which could be reconstructed in future from
Super Nova Acceleration Probe (SNAP) data.
