Kiloelectronvolt-era nucleosynthesis and its implications

A late-decaying particle, e.g., the gravitino, initiates a new phase of nucleosynthesis in the kiloelectronvolt era. The abundances of all light elements, except 4He, are given by the fixed points of the rate equations, agree with observations, and are insensitive to the pre-kiloelectronvolt physics if 4He is not underproduced. Constraints from ordinary nucleosynthesis evaporate, allowing a wide range of values for Ω/sub B/ and the expansion rate: The Universe can be closed by baryons; the number of light ν species can be greater than four; the era of conventional nucleosynthesis can be matter or vacuum-energy dominated