Consequences of a 17-keV neutrino

If the controversial 17-keV neutrino exists, laboratory, astrophysical and cosmological bounds, unless significantly weakened, require that (1) it be a Majorana neutrino and mainly ${\nu }_{\mathrm{\tau }}$; (2) it not be the dark matter of the universe, although its existence would rule out dominant hot dark matter; (3) the ${\nu }_{\mathrm{\mu }}$ be a heavy Majorana neutrino of mass 17 keV or in the range 170–270 keV; and (4) the Mikheyev-Smirnov-Wolfenstein solution to the solar-neutrino problem involve ${\nu }_{\mathit{e}}$ conversion to a light sterile [SU(2)-singlet] neutrino.