Sterile neutrinos and Big Bang Nucleosynthesis in the 3 + 1 scheme

Abstract

We study the effects of adding a sterile neutrino to three active neutrinos (3+ 1 scheme) in the calculation of primordial abundances. Taking the normalization constant (a) of the occupation factor of the sterile neutrino and the active-sterile mixing angle (φ) as free parameters, we calculate the neutrino distribution function and primordial abundances of light nuclei. We set constrains on these parameters by using the available data on the abundances of D, 4He and 7Li. Results are consistent with small values of a and φ. The extracted value of the baryon-to-photon ratio (ηB), which is constrained by the Wilkinson Microwave Anisotropy Probe (WMAP) value ηWMAP B , and Planck observations, depends strongly on the inclusion of the lithium data in the fit.