Baryons and Dark Matter from the Late Decay of a Supersymmetric Condensate

Abstract

The possibility that both the baryon asymmetry and dark matter arise from the late decay of a population of supersymmetric particles is considered. If the decay takes place below the LSP freeze out temperature, a nonthermal distribution of LSPs results. With conserved $R$ parity these relic LSPs contribute to the dark matter density. A net asymmetry can exist in the population of decaying particles if it arises from coherent production along a supersymmetric flat direction. The asymmetry is transferred to baryons if the condensate decays through the lowest order nonrenormalizable operators which couple to $R$ odd combinations of standard model particles. This also ensures at least one LSP per decay. The relic baryon and LSP number densities are then roughly equal. The ratio of baryon to dark matter densities is then naturally $\Omegab / \OmegaLSP \sim {\cal O}(\mb / \mLSP)$. The resulting upper limit on the LSP mass is model dependent but in the range ${\cal O}(30-140)$ GeV. The total relic density is related to the order at which the flat direction which gives rise to the condensate is lifted. The observed density is obtained for a direction which is lifted by a fourth order Planck scale suppressed operator in the superpotential.