Right-Handed Sneutrinos as Curvatons

We consider the possibility that a right-handed sneutrino can serve as the source of energy density perturbations leading to structure formation in cosmology. The cosmological evolution of a coherently oscillating condensate of right-handed sneutrinos is studied for the case where reheating after inflation is due to perturbative inflaton decays. For the case of Dirac neutrinos, it is shown that some suppression of Planck scale-suppressed corrections to the right-handed neutrino superpotential is necessary. cH^2 corrections to the sneutrino mass squared term must also be suppressed during inflation (|c| < 0.1), in which case, depending on the magnitude of |c| during inflation, a significantly blue (if c > 0) or red (if c < 0) perturbation spectrum is possible. R-parity must also be broken in order to ensure that the Universe is not overclosed by LSPs from the late decay (at temperatures 1-10 MeV) of the right-handed sneutrino condensate. The resulting expansion rate during inflation can be significantly smaller than in conventional supersymmetric inflation models (as low as 10^6 GeV is possible). For the case of Majorana neutrinos, a more severe suppression of Planck-suppressed superpotential corrections is required. In addition, the Majorana sneutrino condensate is likely to be thermalised before it can dominate the energy density, which would exclude the Majorana right-handed sneutrino as a curvaton.