Supersymmetric dark matter and the reheating temperature of the universe

Since the thermal history of the universe is unknown before the epoch of primordial nucleosynthesis, the largest temperature of the radiation-dominated phase (the reheating temperature) might have been as low as 1 MeV. We perform a quantitative study of the supersymmetric dark matter relic abundance in cosmological scenarios with low reheating temperature. We show that, for values of the reheating temperature smaller than about 30 GeV, the domains of the supergravity parameter space which are compatible with the hypothesis that dark matter is composed of neutralinos are largely enhanced. We also find a lower bound on the reheating temperature: If the latter is smaller than about 1 GeV neutralinos cannot be efficiently produced in the early universe and then they are not able to explain the present amount of dark matter.