136 research outputs found
Radiative Seesaw Mechanism at Weak Scale
We investigate an alternative seesaw mechanism for neutrino mass generation.
Neutrino mass is generated at loop level but the basic concept of usual seesaw
mechanism is kept. One simple model is constructed to show how this mechanism
is realized. The applications of this seesaw mechanism at weak scale to
cosmology and neutrino physics are discussed.Comment: 12 Pages, latex, no figure
Implications of a Massless Neutralino for Neutrino Physics
We consider the phenomenological implications of a soft SUSY breaking term BN
at the TeV scale (here B is the U(1)_Y gaugino and N is the right-handed
neutrino field). In models with a massless (or nearly massless) neutralino,
such a term will give rise through the see-saw mechanism to new contributions
to the mass matrix of the light neutrinos.
We treat the massless neutralino as an (almost) sterile neutrino and find
that its mass depends on the square of the soft SUSY breaking scale, with
interesting consequences for neutrino physics. We also show that, although it
requires fine-tuning, a massless neutralino in the MSSM or NMSSM is not
experimentally excluded. The implications of this scenario for neutrino physics
are discussed.Comment: 14 pages, latex, no figure
Systematic Study of Fermion Masses and Mixing Angles in Horizontal SU(2) Gauge Theory
Despite its great success in explaining the basic interactions of nature, the
standard model suffers from an inability to explain the observed masses of the
fundamental particles and the weak mixing angles between them. We shall survey
a set of possible extensions to the standard model, employing an SU(2)
``horizontal'' gauge symmetry between the particle generations, to see what
light they can shed on this problem.Comment: 43 pages, 4 figures (available by postal mail on request), OZ-92/0
Planck scale effects in neutrino physics
We study the phenomenology and cosmology of the Majoron (flavon) models of
three active and one inert neutrino paying special attention to the possible
(almost) conserved generalization of the Zeldovich-Konopinski-Mahmoud lepton
charge. Using Planck scale physics effects which provide the breaking of the
lepton charge, we show how in this picture one can incorporate the solutions to
some of the central issues in neutrino physics such as the solar and
atmospheric neutrino puzzles, dark matter and a 17 keV neutrino. These
gravitational effects induce tiny Majorana mass terms for neutrinos and
considerable masses for flavons. The cosmological demand for the sufficiently
fast decay of flavons implies a lower limit on the electron neutrino mass in
the range of 0.1-1 eV.Comment: 24 pages, 1 figure (not included but available upon request), LaTex,
IC/92/196, SISSA-140/92/EP, LMU-09/9
Connecting bimaximal neutrino mixing to a light sterile neutrino
It is shown that if small neutrino masses owe their origin to the
conventional seesaw mechanism and the MNS mixing matrix is in the exact
bimaximal form, then there exist symmetries in the theory that allow one of the
righthanded neutrinos to become naturally massless, making it a candidate for
the sterile neutrino discussed in the literature. Departures from the exact
bimaximal limit leads to tiny mass for the sterile neutrino as well as its
mixing to the active neutrinos. This provides a minimal theoretical framework
where a simultaneous explanation of the solar, atmospheric and LSND
observations within the so-called 3+1 scenario may be possible.Comment: new references added; paper accepted for publication in Phys. Rev.
D.(rapid communications); note adde
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
Simple Model for (3+2) Neutrino Oscillations
We formulate a set of naturalness criteria for sterile neutrinos (\nu') to be
light, needed for reconciling the LSND neutrino anomaly with the other neutrino
data. A light sterile neutrino becomes as natural as the light active neutrinos
if it carries quantum numbers of a chiral gauge symmetry broken at the TeV
scale. The simplest such theory is shown to be an SU(2) gauge theory with the
\nu' transforming as a spin 3/2 multiplet. We develop this model and show that
it leads naturally to the phenomenologically viable (3+2) neutrino oscillation
scheme. We also present next-to-minimal models for light sterile neutrinos
based on a chiral U(1) gauge symmetry.Comment: 12 pages in LaTeX, typos corrected, reference adde
Planck Scale Symmetry Breaking and Majoron Physics
Majoron models provide neutrino masses via the spontaneous breaking of a
global symmetry. However, it may be argued that all global symmetries
will be explicitly violated by gravitational effects. We show that it is
possible to preserve most of the usual features of majoron models by invoking
to be a gauge symmetry and adding a second singlet scalar field.
The majoron gets a small model dependent mass. The couplings of majorons to
neutrinos may be of ordinary strength or may be made arbitrarily weak. We
discuss the cosmological and astrophysical consequences of majoron models in
the context of a model dependent majoron mass and neutrino coupling. For an
appropriate choice of parameters majorons can play the role of dark matter.Comment: 30 pages, UM-TH-92-3
L_e + L_\mu - L_\tau - L_s Symmetry and a Mixed 2+2 Scenario for Neutrino Oscillations
Recent results from SuperKamiokande and SNO experiments have set severe
constraints on possible mixings of a light sterile neutrino, \nu_s, with the
three active species required for a simultaneous explanation of the solar,
atmospheric and LSND neutrino oscillation data. A consistent scheme has emerged
from a global analysis of the data wherein two of the neutrinos are nearly
degenerate with a mass of order 1 eV, that mix significantly with the two
lighter states. We present realizations of such a mixed 2+2 oscillation
scenario based on L_e + L_\mu - L_\tau - L_s symmetry (L_i stands for the ith
lepton number). Breaking of of this lepton number symmetry by a small mass term
for \nu_s leads to the required large mixings for both the atmospheric and the
solar neutrino oscillations. Sum rules for the neutrino oscillation parameters
are derived within this scheme, and are shown to be consistent with present
data. These models predict U_{e3} = 0.02-0.03, which can serve as a test of
this idea. We also present gauge models based on mirror extensions of the
Standard Model that naturally lead to a light sterile neutrino with the
required mixing pattern.Comment: 13 pages, RevTe
Neutrino oscillation constraints on neutrinoless double beta decay
We have studied the constraints imposed by the results of neutrino
oscillation experiments on the effective Majorana mass || that characterizes
the contribution of Majorana neutrino masses to the matrix element of
neutrinoless double-beta decay. We have shown that in a general scheme with
three Majorana neutrinos and a hierarchy of neutrino masses (which can be
explained by the see-saw mechanism), the results of neutrino oscillation
experiments imply rather strong constraints on the parameter ||. From the
results of the first reactor long-baseline experiment CHOOZ and the Bugey
experiment it follows that || < 3x10^{-2} eV if the largest mass-squared
difference is smaller than 2 eV^2. Hence, we conclude that the observation of
neutrinoless double-beta decay with a probability that corresponds to || >
10^{-1} eV would be a signal for a non-hierarchical neutrino mass spectrum
and/or non-standard mechanisms of lepton number violation.Comment: 20 pages, including 4 figure
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