Astrophysics and cosmology confront the 17-keV neutrino.

Abstract

Astrophysical and cosmological arguments constrain the properties of a 17-keV Dirac neutrino. It must have interactions beyond those of the standard electroweak theory to reduce its cosmic abundance by a factor of 200. A predicament arises because the additional helicity states of the neutrino necessary to construct a Dirac mass must have interactions strong enough to evade the astrophysical bound from SN 1987A, but weak enough to avoid violating the bound from primordial nucleosynthesis.