Accelerator, reactor, solar and atmospheric neutrino oscillations: four generation analysis

This work presents a phenomenological analysis of neutrino oscillations in a four generation picture including an additional sterile neutrino besides the three active flavours. In such a framework, more than one scenario is possible that can accommodate three hierarchically different mass squared differences as required by the present experimental data. Two different mass spectra are considered. Choosing the Δm2 values in the ranges suitable for the LSND and atmospheric and solar neutrino oscillations, limits on the mixing angles are derived, consistent with the most restrictive accelerator and reactor data as well as the atmospheric and solar neutrino results. The allowed mixing angles are found to be severely constrained in both cases. For one mass pattern in the combined allowed zone the atmospheric anomaly can be explained by νe-νμ oscillations whereas for the other the νμ-ντ channel is preferred. The accelerator experiments CHORUS and NOMAD have different sensitivities in these regions and they can distinguish between the two choices. (author)