Neutralino and gravitino dark matter with low reheating temperature

Abstract

We examine a scenario in which the reheating temperature TR after inflation is so low that it is comparable to, or lower than, the freeze out temperature of ordinary WIMPs. In this case the relic abundance of dark matter is reduced, thus relaxing the impact of the usually strong constraint coming from the requirement that the universe does not overclose. We first re-examine the dynamics of freezeout during reheating. Next we study the parameter space of the MSSM with ten free parameters, the Constrained MSSM and the singlino-dominated regions of the Next-to-MSSM. In each case we often find dramatic departures from the usually considered regime of high TR, with important implications for direct detection dark matter searches. In particular, in the MSSM we examine WIMP mass range up to about 5 TeV, and we find large regions of bino dark matter over the whole mass range, and of higgsino dark matter with mass over a similar range but starting from the ∼ 1 TeV value of the standard high TR scenario. We show that the prospects for bino detection strongly depend on TR, while the higgsino is for the most part detectable by future one-tonne detectors. The wino, which is excluded in the standard scenario, becomes allowed again if its mass is roughly above 3.5 TeV, and can also be partially detectable. In the CMSSM, the bino and higgsino mass ranges become much more constrained although detection prospects remain roughly similar. In the Next-to-MSSM we show that, at low enough TR wide ranges of singlino-dominated parameter space of the model become again cosmologically allowed, although detection prospects remain nearly hopeless. We also study the non-thermal contribution to the DM relic density from direct and cascade decays of the inflaton. Finally, in the framework of the MSSM we consider the case of a gravitino as dark matter. In this case we find strong bounds from overclosure and from Big Bang Nucleosynthesis, and derive lower limits on TR which depend on the gravitino mass and on the nature of the lightest ordinary superpartner.