Leptogenesis as the source of gravitino dark matter and density perturbations

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.Comment: 12 pages. Cosmetic changes made and references added. Final version to appear in Phys. Rev.

Reheating in supersymmetric high scale inflation

Motivated by Refs \cite{am1,am2}, we analyze how the inflaton decay reheats the Universe within supersymmetry. In a non-supersymmetric case the inflaton usually decays via preheating unless its couplings to other fields are very small. Naively one would expect that supersymmetry enhances bosonic preheating as it introduces new scalars such as squarks and sleptons. On the contrary, we point out that preheating is unlikely within supersymmetry. The reason is that flat directions in the scalar potential, classified by gauge invariant combinations of slepton and squark fields, are generically displaced towards a large vacuum expectation value (VEV) in the early Universe. They induce supersymmetry preserving masses to the inflaton decay products through the Standard Model Yukawa couplings, which kinematically blocks preheating for VEVs $> 10^{13}$ GeV. The decay will become allowed only after the flat directions start oscillating, and once the flat direction VEV is sufficiently redshifted. For models with weak scale supersymmetry, this generically happens at a Hubble expansion rate: $H \simeq (10^{-3}-10^{-1}) {\rm TeV}$, at which time the inflaton decays in the perturbative regime. This is to our knowledge first analysis where the inflaton decay to the Standard Model particles is treated properly within supersymmetry. There are number of important consequences: no overproduction of dangerous supersymmetric relics (particularly gravitinos), no resonant excitation of superheavy dark matter, and no non-thermal leptogenesis through non-perturbative creation of the right-handed (s)neutrinos. Finally supersymmetric flat directions can even spoil hybrid inflation all together by not allowing the auxiliary field become tachyonic.Comment: 13 revtex pages, 2 tables. Title changed, few clarifications added, final version accepted for publication in Phys. Rev.

Unifying inflation and dark matter

We present a simple model where a scalar field is responsible for cosmic inflation and generates the seed for structure formation, while its thermal relic abundance explains dark matter in the universe. The inflaton self-coupling also explains the observed neutrino masses. All the virtues can be attained in a minimal extension of the Standard Model gauge group around the TeV scale. We can also unveil these properties in the forthcoming ground based experiments.Comment: 4 pages, 3 figures. Submitted conference proceedings, based on a talk presented at UCLA DM08 conferenc

Enhanced reheating via Bose condensates

In supersymmetric extensions of the particle physics Standard Model, gauge invariant combinations of squarks and sleptons (flat directions) can acquire large expectation values during a period of cosmological inflation. If the inflaton sector couples to matter fields via these flat directions, then new channels for efficient reheating, in particular via parametric resonance instabilities, are opened up. These can lead to efficient reheating induced by the flat directions even if the bare coupling constants are small. In this Letter we discuss various channels which yield this ``enhanced reheating'' effect, and we address some cosmological consequences.Comment: 6 page