Cosmological implications of light element abundances: theory.

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Abstract
Primordial nucleosynthesis provides (with the microwave background radiation) one of the two quantitative experimental tests of the hot Big Bang cosmological model (versus alternative explanations for the observed Hubble expansion). The standard homogeneous-isotropic calculation fits the light element abundances ranging from H-1 at 76% and He-4 at 24% by mass through H-2 and He-3 at parts in 10(5) down to Li-7 at parts in 10(10). It is also noted how the recent Large Electron Positron Collider (and Stanford Linear Collider) results on the number of neutrinos (N(nu)) are a positive laboratory test of this standard Big Bang scenario. The possible alternate scenario of quark-hadron-induced inhomogeneities is also discussed. It is shown that when this alternative scenario is made to fit the observed abundances accurately, the resulting conclusions on the baryonic density relative to the critical density (OMEGA(b)) remain approximately the same as in the standard homogeneous case, thus adding to the robustness of the standard model and the conclusion that OMEGA(b) almost-equal-to 0.06. This latter point is the driving force behind the need for nonbaryonic dark matter (assuming total density OMEGA(total) = 1) and the need for dark baryonic matter, since the density of visible matter OMEGA(visible) < OMEGA(b). The recent Population II B and Be observations are also discussed and shown to be a consequence of cosmic ray spallation processes rather than primordial nucleosynthesis. The light elements and N(nu) successfully probe the cosmological model at times as early as 1 sec and a temperature (T) of almost-equal-to 10(10) K (almost-equal-to 1 MeV). Thus, they provided the first quantitative arguments that led to the connections of cosmology to nuclear and particle physics.

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