Four-Neutrino Mass Spectra and the Super-Kamiokande Atmospheric Up-Down Asymmetry

TL;DR

This paper investigates four-neutrino mass spectra in light of Super-Kamiokande atmospheric data, finding that only specific mass arrangements with two pairs separated by the LSND gap are compatible with all current neutrino oscillation observations.

Contribution

It demonstrates that most four-neutrino mass spectra are incompatible with Super-Kamiokande data, identifying only two viable schemes with two pairs of close masses separated by the LSND gap.

Findings

Most four-neutrino mass spectra are excluded by Super-Kamiokande data.

Only two specific mass arrangements fit all existing neutrino oscillation data.

Mass spectra with three close neutrino masses separated from the fourth are incompatible with observations.

Abstract

In the framework of schemes with mixing of four massive neutrinos, which can accommodate the atmospheric, solar and LSND ranges of Delta m^2, we show that, in the whole region of Delta m^2_{LSND} allowed by LSND, the Super-Kamiokande up-down asymmetry excludes all mass spectra with a group of three close neutrino masses separated from the fourth mass by the LSND gap of order 1 eV. Only two schemes with mass spectra in which two pairs of close masses are separated by the LSND gap can describe the Super-Kamiokande up-down asymmetry and all other existing neutrino oscillation data.