Do Massive Neutrinos Ionize Intergalactic HI ?

Abstract

The radiative decay of massive relic 30eV neutrinos could explain several observational puzzles including the missing dark matter in the universe and the anomalous degree of ionization of interstellar matter in the Galaxy. We note that various non-standard particle physics models with extended scalar sector or minimal supersymmetry have sufficient freedom to accommodate such neutrinos. We discuss observational constraints in the immediate Solar neighborhood, in nearby regions of low interstellar absorption, in the Galactic halo, in clusters of galaxies, and in extragalactic space. Although some observations have been interpreted as ruling out this picture, we note that this is true only for models in which extreme concentrations of neutrinos occur in clusters of galaxies. An instrument is under development to measure the cosmic diffuse EUV background in the local Solar neighborhood, for flight on the Spanish Minisat satellite platform. This instrument will have the capability of providing a definitive test of the radiative neutrino decay hypothesis.