IMPROVED COSMOLOGICAL CONSTRAINTS ON NEUTRINO-PRODUCING DECAYING PARTICLES

We derive improved cosmological constraints on decaying Particles which produce neutrinos but no electromagnetically or strongly interacting particles in their decay. The neutrinos produced in these decays can annihilate with cosmic background antineutrinos or antineutrinos produced in the decay to yield e+e- pairs which generate cascades of photons that fission light elements. Annihilation off of both background and decay neutrinos is included; we find that the latter is the dominant thermalization and photofission mechanism over most of the parameter range we have examined. Limits on the mass, abundance, and lifetime of neutrino-producing decaying particles are determined from the overproduction of D+He-3 from the fission of He-4. These are combined with limits on the present density of the relativistic decay products to yield lifetime-independent limits on the decaying particle abundance and mass. Results are applied to the specific example of a gravitino which decays into a neutrino and a sneutrino.