The Quantum Phase of Inflation

Inflation models can have an early phase of inflation where the evolution of the inflaton is driven by quantum fluctuations before entering the phase driven by the slope of the scalar field potential. For a Coleman-Weinberg potential this quantum phase lasts 10^7-8 e-foldings. A long period of fluctuation driven growth of the inflation field can possibly take the inflaton past phi_*, the value of the field where our current horizon scale crosses the horizon; alternatively, even if the field does not cross phi_*, the inflaton could have high kinetic energy at the end of this phase. Therefore we study these issues in the context of different models of inflation. In scenarios where cosmological relevant scales leave during the quantum phase we obtain large curvature perturbations of O(10). We also apply our results to quadratic curvaton models and to quintessence models. In curvaton models we find that inflation must last longer than required to solve the horizon problem, that the curvaton models are incompatible with small field inflation models and that there may be too large non-gaussianity. A new phase of thermal fluctuation driven inflation is proposed, in which during inflation the inflaton evolution is governed by fluctuations from a sustained thermal radiation bath rather than by a scalar field potential.