Density Spectrums from Kinetic Inflations

Abstract

The pole-like accelerated expansion stages purely driven by the coupling between the gravity and the dilaton field without referring to the potential term can be realized in a class of generalized gravity theories. We consider three such scenarios based on the scalar-tensor gravity, the induced gravity and the string theory. Quantum fluctuations during the expansion stages (including more general situations) can be derived in exact analytic forms. Assuming that the pole-like acceleration stage provides a viable inflation scenario in the early universe we derive the generated classical density spectrums. The generated classical density field shows a generic tilted spectrum with $n \simeq 4$ which differs from the observed spectrum supporting $n \simeq 1$.