Minimal String Driven Cosmology and its Predictions

We present a minimal model for the Universe evolution fully extracted from effective String Theory. By linking this model with a minimal but well established observational information, we prove that it gives realistic predictions on early and current energy density and its results are compatible with General Relativity. Interestingly enough, the predicted current energy density is found $\mathrm{\Omega }=1$ and in anycase with lower limit $\mathrm{\Omega }\ge 4/9$. On the other hand, the energy density at the exit of inflationary stage gives also $\mathrm{\Omega }{|}_{inf}=1$. This result shows an agreement with General Relativity (spatially flat metric gives critical energy density) within an unequivalent Non-Einstenian context (string low energy effective equations). The order of magnitude of the energy density-dilaton coupled term at the beginning of radiation dominated stage agrees with GUT scale. Without solving the known problems about higher order corrections and graceful exit of inflation, we find this model closer to the observational Universe properties than the current available string cosmology scenarii. At a more fundamental level, this model is by its construction close to the standard cosmological evolution, and it is driven selfconsistently by the evolution of the string equation of state itself. The inflationary String Driven stage is able to reach an enough amount of inflation, describing a Big Bang like evolution for the metric.