Résumé
This work examines the evolution of non-linear sub-horizon scale fluctuations in the entropy-per-baryon between cosmic epochs at temperatures T approximately equals 100 GeV and T approximately equals 1 keV. The evolution of such fluctuations is numerically simulated for wide ranges of initial fluctuation amplitudes and length scales. The simulations include neutrino heat transport, neutron and proton diffusion, photon diffusive heat transport, and hydrodynamic expansion against radiation drag, comprising all the relevant fluctuation damping processes. Neutrino heat transport is treated both in the optically thick limit where the neutrino mean free path is short compared to the fluctuation length scale, and in the optically thin limit where the neutrino mean free path is long compared to the fluctuation length scale. Fluctuation damping processes are coupled to nuclear reactions. Light element abundances emerging from the epoch of primordial nucleosynthesis (T is approximately 100 keV) in the presence of spherically condensed fluctuations are computed. The computed H-2, He-3, He-4, and Li-7 abundance yields are compared with observationally inferred abundances. Fluctuation parameters are identified which lead to significant primordial heavy-element production while still satisfying all the light element abundance constraints. It is found that the existence of spherically condensed fluctuations during the epoch of primordial nucleosynthesis can not increase the upper limit on the cosmic baryon density derived from homogeneous Big Bang nucleosynthesis, primarily due to Li-7 overproduction. Even at lower baryonic densities inhomogeneous Big Bang abundance yields for wide ranges of fluctuation parameters can not be reconciled with observational limits. It is proposed to use this sensitivity of the primordial nucleosynthesis process to fluctuations in entropy-per-baryon for constraining a class of electroweak baryogenesis scenarios at temperature T is approximately 100 GeV. In general, the present study suggests that primordial nucleosynthesis can be employed to place limits on a variety of processes which are capable of generating fluctuations in the entropy-per-baryon prior to the nucleosynthesis era. (Dissert. Abstr.)