DOI 10.1007/s100529900001
Neutrino textures in light of Super-Kamiokande data and a realistic string model
J. Ellis1 - G.K. Leontaris1,2 - S. Lola1 - D.V. Nanopoulos3,4,5
1 Theory Division, CERN, CH-1211 Geneva 23,
Switzerland
2 Theoretical Physics Division, Ioannina University,
GR-45110 Ioannina, Greece
3 Center for Theoretical Physics, Department of Physics,
Texas A&M
University, College Station, TX 77843 4242, USA
4 Astroparticle Physics Group, Houston Advanced Research Center (HARC),
The Mitchell Campus, Woodlands, TX 77381, USA
5 Academy of Athens, Chair of Theoretical Physics, Division of Natural
Sciences,
28 Panepistimiou Ave., Athens GR-10679, Greece
Received: 6 November 1998 / Published online: 18 June 1999
Abstract
Motivated by the Super-Kamiokande
atmospheric neutrino data, we discuss possible textures for Majorana and
Dirac neutrino masses within the see-saw framework.
There are two main purposes of this paper: first, to gain
intuition into this area from a purely phenomenological analysis, and second,
to explore to what extent it may be realized in a specific model.
We comment initially on the simplified two-generation case,
emphasizing that large mixing is not incompatible with a large hierarchy
of mass eigenvalues. We also emphasize that renormalization-group
effects
may amplify neutrino mixing, and we present semi-analytic expressions for
estimating this amplification. Several examples are then given of
three-family neutrino mass textures, which may also accommodate the
persistent solar neutrino deficit, with different assumptions for the
neutrino Dirac mass matrices.
We comment on a few features of neutrino
mass textures arising
in models with a U(1) flavour symmetry. Finally, we
discuss the possible pattern of neutrino masses in a "realistic'' flipped
SU(5) model derived from string theory, illustrating how a desirable
pattern of mixing may emerge.
Both small- or large-angle MSW solutions are possible, while a
hierarchy
of neutrino masses appears more natural than near-degeneracy.
This model contains some
unanticipated features
that may be relevant in other models also:
The neutrino Dirac matrices may not
be related closely to the quark mass matrices, and the heavy Majorana
states may include extra gauge-singlet fields.
Copyright Springer-Verlag
