Cold big bang nucleogenesis

This paper treats the energetic and nucleosynthetic history of a Friedmann model with low photon-baryon ratio eta(gamma) and positive lepton-baryon ra tio eta(L). At early times, such a universe is in equilibrium and is energe tically dominated by particle Fermi energies; at later times photon release from elementary particle decays probably lifts degeneracy of nucleons but not of leptons. After outlining the early history I present the results of full nucleosynthesis calculations for nondegenerate baryons and degenerate electrons and neutrinos. The results show that, for eta(gamma) less than or similar to 0.01 (consistent with the particle-decay heating), the neutron- proton ratio depends strongly on eta(L) and that production of sufficient h elium to match observations creates large primordial metallicity, in agreem ent with a previous argument by Carr for the eta(gamma) = 0 case. Excessive metallicity in the cold model is avoided only if eta(L) is sufficiently hi gh (eta(L) > 1.5 for eta(gamma) = 0; eta(L) greater than or similar to 5 fo r eta(gamma) = 0.01) to suppress all nucleosynthesis before the Population III epoch. The calculations also reveal certain combinations of eta(gamma) greater than or similar to 100 (corresponding to T-0 similar to 0.02) and e ta(L) greater than or similar to 5 that produce acceptable helium yields. T his result contradicts the widespread notion that astrophysical observation s of helium abundance together with nucleosynthesis calculations within a b ig bang model predict the current radiation background temperature.