Thermal and Non-Thermal Production of Gravitinos in the Early Universe

The excessive production of gravitinos in the early universe destroys the successful predictions of nucleosynthesis. The thermal generation of gravitinos after inflation leads to the bound on the reheating temperature, T_{RH}< 10^9 GeV. However, it has been recently realized that the non-thermal generation of gravitinos in the early universe can be extremely efficient and overcome the thermal production by several orders of magnitude, leading to much tighter constraints on the reheating temperature. In this paper, we first investigate some aspects of the thermal production of gravitinos, taking into account that in fact reheating is not instantaneous and inflation is likely to be followed by a prolonged stage of coherent oscillations of the inflaton field. We then proceed by further investigating the non-thermal generation of gravitinos, providing the necessary tools to study this process in a generic time-dependent background with any number of superfields. We also present the first numerical results regarding the non-thermal generation of gravitinos in particular supersymmetric models.