  We extend the constrained minimal supersymmetric model (CMSSM) by adding a
right-handed neutrino superfield ($\nu$CMSSM) which decouples close to the GUT
scale. We study the effects of a right-handed neutrino on the low energy
spectrum and focus on the predictions for dark matter properties. We pay
particular attention to the realization of the light (left-handed) sneutrino
which can be the next-to-lightest supersymmetric particle (NLSP) with either
the neutralino or gravitino as the lightest supersymmetric particle (LSP).
Notably, for the case of a neutralino LSP with a sneutrino NLSP, there are new
`sneutrino coannihilation regions' which yield the desired thermal neutralino
relic density determined by WMAP.
