ASTROPHYSICAL CONSTRAINTS ON MASSIVE UNSTABLE NEUTRAL RELIC PARTICLES

There has recently been renewed interest in massive neutral dark-matter particle candidates with masses greater than approximately 1 TeV which may be unstable. We re-evaluate the constraints on such particles from the possible effects of their decays on the spectrum of the microwave background-radiation and the primordially synthesised abundances of the light elements, from observations of the diffuse gamma-ray background radiation, and from searches for muons and neutrinos in nucleon-decay and cosmic-ray detectors. We find that such unstable neutral relics may well have the cosmological critical density if their lifetime exceeds approximately 10(16) yr. We illustrate our arguments by applying them to technicolour baryons and to "cryptons" in superstring-inspired models.