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

A late-decaying (τ > 10^5^ 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 ^4^He using hadronic showers and ^4^He hadrodestruction. The primordial abundances of D, ^3^He, ^6^Li and ^7^Li 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 ^4^He. Any overabundance of ^4^He is subsequently hadrodissociated. The primordial element abundances are in agreement with observations; furthermore, they are independent of {OMEGA}_B_h^2^_0_ for a very broad range of {OMEGA}beta_h^2^_0_, which includes the previously forbidden range 0.03 <= {OMEGA}_B_h^2^_0_ <= 1.1. An ideal candidate for the late-decaying particle may be the gravitino.