The Effect of Some Nonequilibrium Processes on the Primordial Nucleosynthesis

Abstract

The effect of nonequilibrium processes, namely nonequilibrium decays of light particles and nonequilibrium neutrino oscillations, on primordial nucleosynthesis is investigated. First, a modification of the standard big-bang nucleosynthesis scenario with additional light (m_x=O(MeV)) quasistable particles (t ~ 1 s) decaying xinto $v\bar v$ is considered. It is proved that in case the decay products do not thermalize they change the kinetics of the neutron-proton transitions and respestively the abundance of the light elements produced primordially. In case of primordial nucleosynthesis with neutrino oscillations a concrete model of oscillations between active and nonthermalized sterile neutrinos is investigated. The effect on the production of helium-4 has been proved considerable for a certain range of oscillation parameters. Thus, stringent constraints on the oscillation parameters were obtained.