A 4-NEUTRINO MIXING SCHEME FOR OBSERVED NEUTRINO DATA

It has been observed that simultaneous explanation of the solar and at mospheric neutrino deficits and the reported evidence for v(mu) --> v( e) oscillation from the Los Alamos Liquid Scintillator Detector (LSND) requires at least one extra neutrino species in addition to the three known ones. The extra neutrino must be sterile with respect to the kn own weak interactions. We present a new mass matrix for these four neu trinos in which the LSND effect and the atmospheric neutrino deficit a re governed by only one parameter. We investigate the phenomenological implications of such a mass matrix ansatz and suggest possible ways t o understand it in gauge theories. (C) 1998 Published by Elsevier Scie nce B.V. All rights reserved.