EFFECT OF NEUTRINO OSCILLATION ON PRIMORDIAL NUCLEOSYNTHESIS

Primordial nucleosynthesis is one of the best tools to investigate the ear ly-universe model. Standard big-bang nucleosynthesis (SBBN) could predict or determine some important cosmological parameters, baryon-t o-photon ratio, number of neutrino species, etc. After remarkable succ ess of SBBN, there was a lot of valiant nucleosynthesis, that is degen erate neutrinos, inhomogeneous matter distribution, varying gravitatio nal constant, etc. All of these models assume that all neutrinos are m assless, but actually we have only the upper bound for those masses. I f we allow neutrino to get a non-zero mass, the picture will be change d. Non-zero neutrino mass causes neutrino oscillation between neutrino species. This neutrino oscillation is well studied to solve the solar -neutrino problems. Here me will study the basic theoretical backgroun d for the effect of massive neutrinos on primordial nucleosynthesis.