Effects of sterile neutrino and extra-dimension on big bang nucleosynthesis

TL;DR

This paper explores how extra-dimensional sterile neutrinos influence big bang nucleosynthesis, constraining parameters by analyzing their effects on cosmic expansion, neutrino mixing, and element abundances.

Contribution

It introduces a model incorporating extra-dimensional sterile neutrinos into BBN, analyzing their impact on expansion rate, neutrino mixing, and relic abundance, with new constraints derived from observational data.

Findings

Relic abundance of sterile neutrinos is significantly enhanced by extra dimensions.

Resonance effects in neutrino mixing can drastically alter reaction rates.

Constraints on extra dimension parameters are derived from light element abundances.

Abstract

By assuming the existence of extra-dimensional sterile neutrinos in big bang nucleosynthesis (BBN) epoch, we investigate the sterile neutrino ($\nu_{\rm s}$) effects on the BBN and constrain some parameters associated with the $\nu_{\rm s}$ properties. First, for cosmic expansion rate, we take into account effects of a five-dimensional bulk and intrinsic tension of the brane embedded in the bulk, and constrain a key parameter of the extra dimension by using the observational element abundances. Second, effects of the $\nu_{\rm s}$ traveling on or off the brane are considered. In this model, the effective mixing angle between a $\nu_{\rm s}$ and an active neutrino depends on energy, which may give rise to a resonance effect on the mixing angle. Consequently, reaction rate of the $\nu_{\rm s}$ can be drastically changed during the cosmic evolution. We estimated abundances and temperature of the $\nu_{\rm s}$ by solving the rate equation as a function of temperature until the sterile neutrino decoupling. We then find that the relic abundance of the $\nu_{\rm s}$ is drastically enhanced by the extra-dimension and maximized for a characteristic resonance energy $E_{\rm res}\gtrsim 0.01$ GeV. Finally, some constraints related to the $\nu_{\rm s}$, mixing angle and mass difference, are discussed in detail with the comparison of our BBN calculations corrected by the extra-dimensional $\nu_{\rm s}$ to observational data on light element abundances.