Neutralino Dark Matter in Scenarios with Early Matter Domination
  We investigate the production of neutralino dark matter in a cosmological
scenario featuring an early matter dominated era ending at a relatively low
reheating temperature. In such scenarios different production mechanisms of
weakly interacting massive particles (WIMPs), besides the well--studied thermal
production, can be important. This opens up new regions of parameter space
where the lightest neutralino, as the best--known supersymmetric (SUSY) WIMP,
obtains the required relic abundance. Many of these new sets of parameters are
also compatible with current limits from colliders as well as direct and
indirect WIMP searches. In particular, in standard cosmology bino--like
neutralinos, which emerge naturally as lightest neutralino in many models, can
have the desired relic density only in some finetuned regions of parameter
space where the effective annihilation cross section is enhanced by
co--annihilation or an $s-$channel pole. In contrast, if the energy density of
the universe was dominated by long--lived PeV--scale particles (e.g. moduli or
Polonyi fields), bino--like neutralinos can obtain the required relic density
over wide regions of supersymmetric parameter space. We identify the
interesting ranges of mass and decay properties of the heavy long--lived
particles, carefully treating the evolution of the temperature of the thermal
background.
