  Standard simple assumptions are usually made about the pre-Big Bang
Nucleosynthesis epoch, from which we do not have observations. Modifying these
assumptions, the predicted density of relic particles such as neutralinos and
sterile neutrinos can be very different from that in the standard case. For
example, neutralinos could have the dark matter density in (almost) any
supersymmetric model, and sterile neutrinos with mixings large enough to be
soon detected in neutrino experiments would become cosmologically acceptable.
These possibilities are important in view of what the LHC, and neutrino
experiments could soon find.
