Imprint of Sterile Neutrinos in the Cosmic Microwave Background   Radiation
  The existence of low-mass sterile neutrinos is suggested by the current status of solar and atmospheric neutrinos together with the LSND experiment. In typical four-flavor scenarios, neutrinos would contribute to a cosmic hot dark matter component and to an increased radiation content at the epoch of matter-radiation equality. These effects leave their imprint in sky maps of the cosmic microwave background radiation (CMBR) and may thus be detectable with the precision measurements of the upcoming MAP and PLANCK missions. 
Steen Hannestad and Georg Raffelt