Calculation of primordial abundances of light nuclei including a heavy sterile neutrino

TL;DR

This paper investigates how a heavy sterile neutrino affects primordial light nuclei abundances, deriving constraints on neutrino parameters and confirming the persistent lithium problem despite the new physics inclusion.

Contribution

It introduces a detailed calculation of primordial abundances including a heavy sterile neutrino and constrains its parameters using observational data.

Findings

Constraints on sterile neutrino parameters: a<0.60, sin^2 φ=0.15, m_s≈4 keV.

Baryon-to-photon ratio consistent with Planck and WMAP data.

The lithium-7 abundance anomaly remains unresolved.

Abstract

We include the coupling of a heavy sterile neutrino with active neutrinos in the calculation of primordial abundances of light-nuclei. We calculate neutrino distribution functions and primordial abundances, as functions depending on a renormalization of the sterile neutrino distribution function $(a)$, the sterile neutrino mass $(m_s)$ and the mixing angle $(\phi)$. Using the observable data, we set constrains on these parameters, which have the values $a < 0.60$, $\sin^2 \phi=0.15$ and $m_s \approx 4$ keV, for a fixed value of the baryon to photon ratio. When the baryon to photon ratio is allowed to vary, its extracted value is in agreement with the values constrained by Planck observations and by the Wilkinson Microwave Anisotropy Probe (WMAP). It is found that the anomaly in the abundance of $^7$Li persists, in spite of the inclusion of a heavy sterile neutrino.