On the chaoticity of active-sterile neutrino oscillations in the early universe

TL;DR

This paper studies the complex and sensitive evolution of neutrino asymmetries in the early universe, revealing chaotic-like behavior that impacts cosmological processes like BBN and CMB.

Contribution

It demonstrates the presence of chaotic transitions in active-sterile neutrino oscillations and analyzes their implications for early universe cosmology.

Findings

Neutrino asymmetry evolution is highly sensitive to initial conditions.

The system exhibits chaotic transitions but retains some information about initial states.

Final asymmetry signs can be stochastic due to information loss.

Abstract

We have investigated the evolution of the neutrino asymmetry in active-sterile neutrino oscillations in the early universe. We find that there are large regions of parameter space where the asymmetry is extremely sensitive to variations in the initial asymmetry as well as the external parameters (the mass difference and the mixing angle). In these regions the system undergoes chaotic transitions; however, the system is never truly chaotic in the sense that all information about initial conditions is lost. In some cases though, enough information is lost that the final sign of the neutrino asymmetry is stochastic. We discuss the implications of our findings for Big Bang nucleosynthesis (BBN) and the cosmic microwave background (CMB).