Inflation and Oscillations of Universe in 4D Dilatonic Gravity

Abstract

We investigate the inflation of Universe in a model of four dimensional dilatonic gravity with a massive dilaton field $\Phi$. The dilaton plays simultaneously the roles of an inflation field and a quintessence field. It yields a sequential {\em hyper}-inflation with a graceful exit to asymptotic de Sitter space-time, which is an attractor, and is approached as $\exp(-\sqrt{3\Lambda^{obs}} ct/2)$. The time duration of the inflation is reciprocal to the the mass of the dilaton: $\Delta t_{infl}\sim m_{{}_\Phi}^{-1}$. The typical number of e-folds in the simplest model of this type is shown to be realistic without fine tuning.