Is the universe closed by baryons? Nucleosynthesis with a late-decaying massive particle

A late-decaying (τ > 10⁵^ s), massive (M >~ 10 GeV) particle initiates a new phase of nucleosynthesis in the keV era. Light-element production takes place when the hadronic decay products interact with the ambient protons and ⁴He using hadronic showers and ⁴He hadrodestruction. The primordial abundances of D, ³He, ⁶Li and ⁷Li are given by the fixed points of the corresponding rate equations in which hadroproduction balances photodestruction. Since fixed points erase all previous memory, the primordial abundances of these elements are completely independent of the physics before the keV era, whose only important role is to provide at least the observed abundance of ⁴He. Any overabundance of ⁴He is subsequently hadrodissociated. The primordial element abundances are in agreement with observations; furthermore, they are independent of OMEGABₕ²^₀_ for a very broad range of OMEGAbetaₕ²^₀_, which includes the previously forbidden range 0. 03 <= OMEGABₕ²^₀_ <= 1. 1. An ideal candidate for the late-decaying particle may be the gravitino.