COSMOLOGICAL IMPLICATIONS OF LIGHT-ELEMENT ABUNDANCES - THEORY

Primordial nucleosynthesis provides (with the microwave background rad iation) one of the two quantitative experimental tests of the hot Big Bang cosmological model (versus alternative explanations for the obser ved 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 par ts in 10(10). It is also noted how the recent Large Electron Positron Collider (and Stanford Linear Collider) results on the number of neutr inos (N(nu)) are a positive laboratory test of this standard Big Bang scenario. The possible alternate scenario of quark-hadron-induced inho mogeneities is also discussed. It is shown that when this alternative scenario is made to fit the observed abundances accurately, the result ing conclusions on the baryonic density relative to the critical densi ty (OMEGA(b)) remain approximately the same as in the standard homogen eous 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 t he 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 r ecent Population II B and Be observations are also discussed and shown to be a consequence of cosmic ray spallation processes rather than pr imordial nucleosynthesis. The light elements and N(nu) successfully pr obe the cosmological model at times as early as 1 sec and a temperatur e (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.