Active-sterile neutrino oscillations in the early universe with dynamical neutrino asymmetries

Abstract

In the last recent years different anomalies observed in short-baseline neutrino oscillation experiments seem to point towards the existence of light sterile neutrinos. These sterile neutrinos can also be produced in the early universe by oscillations of the active neutrinos and can affect different cosmological observables. In order to quantify the abundance of sterile neutrinos, we perform a detailed study of the flavor evolution in (3+1) and (2+1) oscillation schemes, in presence of dynamical primordial neutrino asymmetries L. We find that for |L|≲10−4eV sterile neutrinos would be completely thermalized creating a tension with the cosmological data. An asymmetry of |L|≳10−3 is then required in order to suppress the sterile production and to reconcile them with cosmology.