On chaoticity of the amplification of the neutrino asymmetry in the early universe

TL;DR

This paper numerically investigates how neutrino asymmetry amplification in the early universe can exhibit chaotic behavior, affecting primordial element abundance predictions and depending sensitively on oscillation parameters.

Contribution

It demonstrates the presence of chaotic regions in neutrino asymmetry amplification, highlighting the sensitivity of the final asymmetry sign to initial conditions and parameters.

Findings

Final asymmetry sign is highly sensitive to oscillation parameters.

Existence of chaotic and robust regions in parameter space.

In chaotic regions, helium abundance predictions are inherently uncertain.

Abstract

We consider numerically the growth of neutrino asymmetry in active-sterile neutrino oscillations in the early universe. It is shown that the final sign of the asymmetry can be highly sensitive to small variations of the oscillation parameters. We find regions which are completely or partially chaotic, but also regions where the sign remains very robust. The consequences for atmospheric neutrino oscillations and primordial nucleosynthesis are then discussed. In the completely chaotic region the predicted He(4)-abundance has an inherent arbitrariness \Delta Y \simeq 0.01.