Light Sterile Neutrinos: Oscillations and Cosmology

Abstract

Light sterile neutrinos with a mass around 1 eV have been studied for many years as a possible explanation of the so called short-baseline neutrino oscillation anomalies. Recently, several neutrino oscillation experiments reported preferences for non-zero values of the mixing angles and squared mass differences for active-sterile mixing, which however are not always in agreement. I review our current knowledge of the light sterile neutrino in the 3+1 model, starting with a separate discussion on the status of the most relevant searches and then analyzing the problems that arise when combining different probes in a global fit. A short summary on the tension with cosmological observations is also provided.

Studies of Non-standard Particle Mixings Through Singular Values

“…Let us consider the case with one additional neutrino. For a review of experimental and global fits in the 3+1 case, see [20]. In such a scenario, the complete matrix is a 4 × 4 unitary matrix and the 3-dimensional contractions belong to the subset V 1 (12), i.e., only one singular value is strictly less than unity.…”