Gauge-Invariant Scalar Perturbations in the New Inflationary Universe

The time evolution of scalar perturbations in the new inflationary universe is investigated by using an extended version of Bardeen’s gauge-invariant formulation. We show that depending on the matter contents of the background space-time the existence of exponentially expanding state either gives rise to large amplitude density perturbations of results in the amplification of initially existing perturbations. Then, for the universe which was homogeneous enough at small scales, we discuss the possibility of generating density perturbations from fluctuations associated with the cosmological particle creation.