微中子的逸散度對早期微中子及宇宙演化之影響

Abstract

Neutrinos are important for the evolution of early universe. The abundance of neutrinos will affect the expansion rate of universe and so that affect the Big Bang nucleosynthesis and cosmic microwave background. In this paper, the consequences of a nonzero neutrino fugacity in the early universe are considered. In contrast to the standard chemical potential, which controls the asymmetry between the number density of neutrinos and anti-neutrinos, fugacity determines the total number density of neutrinos and anti-neutrinos, which is essential in describing the neutron evolution in the early universe. I will introduce the physics about the early universe and some physics about neutrino first. Then an approximate solution to the neutrino Lepton asymmetry is derived from the neutrino quantum kinetic equations and used to study the influence of neutrino fugacity. Also the numerical result will be shown in this paper. In the end, the impact of neutrino’s fugacity on Big Bang Nucleosynthesis (BBN) and Cosmic Microwave Background (CMB) via effective number Neff of neutrinos will be discussed.