Active-sterile neutrino oscillations in the early Universe: asymmetry generation at low |delta m^2| and the Landau-Zener approximation

Abstract

It is well established that active-sterile neutrino oscillations generate large neutrino asymmetries for very small mixing angles (${\sin }^{2}2{\theta }_0\lesssim 10^{-4}$), negative values of $\delta m^2$ and provided that $|\delta m^2|\gtrsim 10^{-4}\mathrm{e}{\mathrm{V}}^2$. By numerically solving the quantum kinetic equations, we show that the generation still occurs at much lower values of $|\delta m^2|$. We also describe the borders of the generation at small mixing angles and show how our numerical results can be analytically understood within the framework of the Landau-Zener approximation thereby extending previous work based on the adiabatic limit. This approximate approach leads to a fair description of the MSW dominated regime of the neutrino asymmetry evolution and is also able to correctly reproduce its final value. We also briefly discuss the impact that neutrino asymmetry generation could have on big bang nucleosynthesis, CMBR and relic neutrinos.

29 pages, 8 figures; to appear on Phys. ReV. D; figure 7 added, new curves in figure 5a, new figure 6

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• Constraint on the Effective Number of Neutrino Species from the WMAP and SDSS LRG Power Spectra
• Cold Dark Matter from heavy Right-Handed neutrino mixing
• Lepton Number-Driven Sterile Neutrino Production in the Early Universe
• Octet baryon magnetic moments in light cone QCD sum rules
• Probing relic neutrino decays with 21 cm cosmology
• Joint constraints on the lepton asymmetry of the Universe and neutrino mass from the Wilkinson Microwave Anisotropy Probe
• Density matrix calculation of the dark matter abundance in the Higgs induced right-handed neutrino mixing model
• The cosmological information on neutrino mixing
• Boomerang mechanism explaining the excess radio background