Inverse decays and the relic density of the sterile sneutrino
  We consider a weak scale supersymmetric seesaw model where the Higgsino is the next-to-lightest supersymmetric particle and the right-handed sneutrino is the dark matter candidate. It is shown that, in this model, inverse decays, which had been previously neglected, may suppress the sneutrino relic density by several orders of magnitude. After including such processes and numerically solving the appropriate Boltzmann equation, we study the dependence of the relic density on the mu parameter, the sneutrino mass, and the neutrino Yukawa coupling. We find that, even though much smaller than in earlier calculations, the sneutrino relic density is still larger than the observed dark matter density. 
Carlos E. Yaguna