  We propose a new mechanism to generate density perturbations in inflationary
models. Spatial fluctuations in the decay rate of the inflaton field to
ordinary matter lead to fluctuations in the reheating temperature. We argue
that in most realistic models of inflation the coupling of the inflaton to
normal matter is determined by the vacuum expectation values of fields in the
theory. If those fields are light during inflation (this is a generic situation
in the minimal models of supersymmetric inflation) they will fluctuate leading
to density perturbations through the proposed mechanism. We show that these
fluctuations could easily dominate over the ones generated through the standard
mechanism. The new scenario has several consequences for inflation model
building and observations. The proposed mechanism allows to generate the
observed level of density perturbations with a much lower scale of inflation
and thus generically predicts a smaller level of gravitational waves. The
relation between the slope of the spectrum of the produced density
perturbations and the potential of the inflaton field is different from the
standard relations obtained in the context of slow roll inflation. Because the
field responsible for the fluctuations is not the inflaton, it can have
significantly larger self couplings and thus density perturbations could be
non-Gaussian. The non-Gaussianity can be large enough to be detectable by CMB
and Large Scale Structure observations.
