Induced-gravity inflation and the density perturbation spectrum

Recent experimental determinations of the spectral index describing the scalar mode spectrum of density perturbations encourage comparison with predictions from models of the very early universe. Unhke extended inflation, Induced-gravity Inflation predicts a power spectrum with 0.98 _< ns _< 1.00, in close agreement with the experimental measurements. An exciting test for models of the very early universe stems from recent measurements of the power spectrum of density perturbations, as seen in the cosmic microwave background radiation. The scalar spectrum, modeled as 79(k) oc k ns [1], functions as a test for models like infation, independently of the familiar test based on the magnitude of the fluctuations. As pointed out by Andrew Liddle and David Lyth [2], extended inflation predicts a spectral index (ns) which is tilted too far away from the Harrison-Zel'dovich (scale-invariant) spectrum (ns = 1.00), and hence cannot match the recent Cosmic Background Explorer (COBE) determination. In this Letter, the predictions from a cousin-model of extended inflation, Induced-gravity Inflation, are compared with the experimental values. Unlike extended inflation, Induced-gravity Inflation predicts a spectral index in quite close agreement with recent experimental values. Like extended inflation [ 3 ], Induced-gravity Inflation (IgI) [4-6] incorporates a Generalized Einstein Theory (GET) gravity sector. Yet unlike extended in