Can active-sterile neutrino oscillations lead to chaotic behavior of the cosmological lepton asymmetry?

While the cosmic baryon asymmetry has been measured at high accuracy to be 6.1 × 10−10, a corresponding lepton asymmetry could be as large as 10−2 if it hides in the neutrino sector. It has been known for some time that such an asymmetry could be generated from a small initial asymmetry given the existence of a sterile neutrino with a mass less than the mass of the active neutrino. While the magnitude of the final lepton asymmetry is deterministic, its sign has been conjectured to be chaotic in nature. This has been proven in the single momentum approximation, also known as the quantum rate equations, but has up to now not been established using the full momentum dependent quantum kinetic equations. Here we investigate this problem by solving the quantum kinetic equations for a system of 1 active and 1 sterile neutrino on an adaptive grid. We show that by increasing the resolution, oscillations in the lepton asymmetry can be eliminated so the sign of the final lepton asymmetry is in fact deterministic. This paper also serves as a launch paper for the adaptive solver LASAGNA which is available at http://users-phys.au.dk/steen