Leptogenesis as the source of gravitino dark matter and density perturbations

Abstract

We investigate the possibility that the entropy producing decay of a right-handed sneutrino condensate can simultaneously be the source of the baryon asymmetry, of gravitino dark matter, and of cosmological density perturbations. For generic values of soft supersymmetry breaking terms in the visible sector of 1-10 TeV, condensate decay can yield the dark matter abundance for gravitinos in the mass range 1 MeV to 1 TeV, provided that the resulting reheat temperature is below $10^6$ GeV. The abundance of thermally produced gravitinos before and after sneutrino decay is then negligible. We consider different leptogenesis mechanisms to generate a sufficient asymmetry, and find that low-scale soft leptogenesis works most naturally at such temperatures. The condensate can easily generate sufficient density perturbations if its initial amplitude is $\sim {\cal O}(M_{\rm GUT})$, for a Hubble expansion rate during inflation $> 10^9$ GeV. Right-handed sneutrinos may therefore at the same time provide a source for baryogenesis, dark matter and the seed of structure formation.