Open AccessActive-sterile neutrino oscillations in the early Universe with the complete mixing matrix
Author(s) -
S. Pastor
Publication year - 2020
Publication title -
journal of physics. conference series
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.21
H-Index - 85
eISSN - 1742-6596
pISSN - 1742-6588
DOI - 10.1088/1742-6596/1468/1/012005
Subject(s) - neutrino , sterile neutrino , physics , mixing (physics) , thermalisation , particle physics , mass matrix , momentum (technical analysis) , universe , planck , kinetic energy , neutrino oscillation , astrophysics , quantum mechanics , finance , economics
In the framework of a 3+1 scheme with an additional inert state, we consider the thermalisation of sterile neutrinos in the early Universe taking into account the full 4 × 4 mixing matrix. The evolution of the neutrino energy distributions is found solving the momentum-dependent kinetic equations with full diagonal collision terms. The degree of thermalisation of the sterile state is shown in terms of the effective number of neutrinos, N eff , and its dependence on the three additional mixing angles ( θ 14 , θ 24 , θ 34 ) and on the squared mass difference ∆ m 2 41 is discussed. Our results are relevant for fixing the contribution of a fourth light neutrino species to the cosmological energy density, whose value is very well constrained by the final Planck analysis. For the preferred region of active-sterile mixing parameters from short-baseline neutrino experiments, we find that the fourth state is fully thermalised ( N eff ≃ 4).