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 ratio eta(L). At early times, such a universe is in equilibrium and is energetically 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 helium to match observations creates large primordial metallicity, in agreement 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 high (eta(L) > 1.5 for eta(gamma) = 0; eta(L) greater than or similar to 5 for 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 eta(L) greater than or similar to 5 that produce acceptable helium yields. This result contradicts the widespread notion that astrophysical observations of helium abundance together with nucleosynthesis calculations within a big bang model predict the current radiation background temperature.