Cosmology, astrophysics, and a 17 keV neutrino

Recent observations of structure below the endpoint in various beta decay spectra suggest that the cosmological consequences of a possible 17 keV neutrino admixture with the electron neutrino should be re-considered. We derive constraints coming from the evolution of the universe, large scale structure, and big bang nucleosynthesis. Whe these are combined with a constraints from astrophysical observables, including neutrinos from SN1987A, the restrictions on models are quiet severe. One model motivated by the recent data appears unacceptable, and the class of models which manages to cleanly satisfy all the constraints appears incompatible with the MSW solution to the solar neutrino problem.