550 research outputs found
Radiatively Generated Oscillations: General Analysis, Textures and Models
We study the consequences of assuming that the mass scale
corresponding to the solar neutrino oscillations and mixing angle
corresponding to the electron neutrino oscillation at CHOOZ are radiatively
generated through the standard electroweak gauge interactions. All the leptonic
mass matrices having zero and at a high scale lead to
a unique low energy value for the which is determined by the
(known) size of the radiative corrections, solar and the atmospheric mixing
angle and the Majorana mass of the neutrino observed in neutrinoless double
beta decay. This prediction leads to the following consequences: () The MSSM
radiative corrections generate only the dark side of the solar neutrino
solutions. () The inverted mass hierarchy () at the high scale
fails in generating the LMA solution but it can lead to the LOW or vacuum
solutions. () The generated in models with maximal solar
mixing at a high scale is zero to the lowest order in the radiative parameter.
It tends to get suppressed as a result of this and lies in the vacuum region.
We discuss specific textures which can lead to the LMA solution in the present
framework and provide a gauge theoretical realization of this in the context of
the seesaw model.Comment: 19 pages, LATE
Fast Neutrino Decay in the Minimal Seesaw Model
Neutrino decay in the minimal seesaw model containing three right handed
neutrinos and a complex singlet Higgs in addition to the
standard model fields is considered. A global horizontal symmetry is
imposed, which on spontaneous breaking gives rise to a Goldstone boson. This
symmetry is chosen in a way that makes a) the contribution of heavy (
MeV) majorana neutrinos to the neutrinoless double beta decay amplitude
vanish and b) allows the heavy neutrino to decay to a lighter neutrino and the
Goldstone boson. It is shown that this decay can occur at a rate much faster
than in the original Majoron model even if one does not introduce any
additional Higgs fields as is done in the literature. Possibility of describing
the 17 keV neutrino in this minimal seesaw model is investigated. While most of
the cosmological and astrophysical constraints on the 17 keV neutrino can be
satisfied in this model, the laboratory limits coming from the neutrino
oscillations cannot be easily met. An extension which removes this inadequacy
and offers a consistent description of the 17 keV neutrino is discussed.Comment: 16 pages, PRL-TH/92-1
Predictive Framework with a Pair of Degenerate Neutrinos at a high scale
Radiative generation of the solar scale is discussed in the
presence of leptonic CP violation. We assume that both the solar scale and
are zero at a high scale and the weak radiative corrections generate
them. It is shown that all leptonic mass matrices satisfying these requirements
lead to a unique prediction for the solar scale in terms of the
radiative correction parameter , the physical solar (atmospheric)
mixing angles and the Majorana neutrino mass
probed in neutrinoless double beta decay. This relation is independent
of the mixing matrix and CP-violating phases at the high scale. The presence of
CP-violating phases leads to dilution in the solar mixing angle defined at the
high scale. Because of this, bi-maximal mixing pattern at the high energy leads
to large but non-maximal solar mixing in the low-energy theory. An illustrative
model with this feature is discussed.Comment: 15 pages, including a postscript figur
Implications of partially degenerate neutrinos at a high scale in the light of KamLAND and WMAP
Electroweak radiative corrections can generate the neutrino (mass)
difference required for the large mixing angle solution (LMA) to the solar
neutrino problem if two of the neutrinos are assumed degenerate at high energy.
We test this possibility with the existing experimental knowledge of the low
energy neutrino mass and mixing parameters. We derive restrictions on ranges of
the high scale mixing matrix elements and obtain predictions for the low energy
parameters required in order to get the LMA solution of the solar neutrino
problem picked out by KamLAND. We find that in the case of standard model this
is achieved only when the (degenerate) neutrino masses lie in the range
(0.7-2) \eV which is at odds with the cosmological limit m_{\nu}<0.23 \eV
(at ) established recently using WMAP results. Thus SM radiative
corrections cannot easily generate the LMA solution in this scenario. However,
the LMA solution is possible in case of the MSSM electroweak corrections with
(almost) degenerate spectrum or with inverted mass hierarchy for limited ranges
in the high scale parameters.Comment: 15 pages, LATEX includes five postscript figure
Breaking of B-L in superstring inspired E6 model
In the framework of the superstring inspired E6 model, low-energy extensions
of the standard model compatible with leptogenesis are considered and masses of
right-handed neutrinos in two scenarios allowed by long-lived protons are
discussed. The presence of two additional generations allows breaking of B-L
without generating nonzero vacuum expectation values of right-handed sneutrinos
of the three known generations. After the symmetry breaking, right-handed
neutrinos acquire Majorana masses of order of 10^11 GeV. Within the framework
of a simple discrete symmetry, assumptions made to provide a large mass of
right-handed neutrinos are shown to be self-consistent. Supersymmetric
structure of the theory ensures that large corrections, associated with the
presence of a (super)heavy gauge field, cancel out.Comment: 18 pages, 6 tables, axodraw use
Phenomenology of Pseudo Dirac Neutrinos
We formulate general conditions on neutrino mass matrices under
which a degenerate pair of neutrinos at a high scale would split at low scale
by radiative corrections involving only the standard model fields. This
generalizes the original observations of Wolfenstein on pseudo Dirac neutrinos
to three generations. A specific model involving partially broken discrete
symmetry and solving the solar and atmospheric anomalies is proposed. The
symmetry pattern of the model naturally generates two large angles one of which
can account for the large angle MSW solution to the solar neutrino problem.Comment: 15 pages LATE
Neutrino Anomalies in an Extended Zee Model
We discuss an extended model which naturally leads to mass
scales and mixing angles relevant for understanding both the solar and
atmospheric neutrino anomalies. No right-handed neutrinos are introduced in the
model.The model uses a softly broken symmetry. Neutrino
masses arise only at the loop level. The one-loop neutrino masses which arise
as in the Zee model solve the atmospheric neutrino anomaly while breaking of
generates at two-loop order a mass splitting needed for
the vacuum solution of the solar neutrino problem. A somewhat different model
is possible which accommodates the large-angle MSW resolution of the solar
neutrino problem.Comment: 11 pages including 2 figures; a reference added and text changed
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