Seminar:   Neff and Neutrino Oscillations: role of the sterile neutrino and of neutrino asymmetry
Ninetta Saviano, Univ. Hamburg & Univ. Naples

Tuesday, February 19 ^th, 2013 ….. 12:00 at Basement Floor’s Room, Institutes Building (UVEG)
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 particular, sterile neutrinos can contribute as extra radiation to the non electromagnetic energy density, usually expressed in terms of the effective number of thermalized neutrino species Neff. In order to compare the forthcoming Planck data on extra radiation with the possibility of sterile neutrino it is necessary a systematic study of their abundance with parameters consistent with the interpretations of short-baseline neutrino oscillation experiments. At this regard, we perform a detailed study of the flavor evolution in different active-sterile oscillation schemes, in presence of dynamical primordial neutrino asymmetries. Moreover we discuss the impact on BBN of significant distortions produced in the electron (anti)neutrino spectra in presence of large asymmetries.