Diffusion coefficients of nucleons in the inhomogeneous big-bang model

Abstract

Recent investigations of the effects of inhomogeneities generated by the quark-hadron phase transition in the early universe on the primordial nucleosynthesis have shown that the difference in the mean free paths of neutrons and protons and the resulting diffusive segregation have a significant influence on the cosmological abundances of the light elements. We calculate the diffusion coefficients of neutrons and protons moving through the background electron, positron and photon gases and their mutual diffusion coefficient, which are important inputs in the nucleosynthesis calculations, in the framework of relativistic kinetic theory in the temperature range 7 × 10⁷ ≤ T ≤ 3 × 10⁹K. The coefficients are shown to have explicit dependence on density and temperature.