739 research outputs found
Nonzero and Neutrino Masses from Modified Neutrino Mixing Matrix
The nonzero and relatively large have been reported by Daya
Bay, T2K, MINOS, and Double Chooz Collaborations. In order to accommodate the
nonzero , we modified the tribimaximal (TB), bimaxima (BM), and
democratic (DC) neutrino mixing matrices. From three modified neutrino mixing
matrices, two of them (the modified BM and DC mixing matrices) can give nonzero
which is compatible with the result of the Daya Bay and T2K
experiments. The modified TB neutrino mixing matrix predicts the value of
greater than the upper bound value of the latest experimental
results. By using the modified neutrino mixing matrices and impose an
additional assumption that neutrino mass matrices have two zeros texture, we
then obtain the neutrino mass in normal hierarchy when
for the neutrino mass matrix from the
modified TB neutrino mixing matrix and for
the neutrino mass matrix from the modified DC neutrino mixing matrix. For these
two patterns of neutrino mass matrices, either the atmospheric mass squared
difference or the solar mass squared difference can be obtained, but not both
of them simultaneously. From four patterns of two zeros texture to be
considered on the obtained neutrino mass matrix from the modified BM neutrino
mixing matrix, none of them can predict correctly neutrino mass spectrum
(normal or inverted hierarchy).Comment: 13 pages, no figure, some references added, and slight revision due
to reviewer(s) comments, to be published in IJMP
Large theta_13 from a model with broken L_e-L_mu-L_tau symmetry
Recent data in the neutrino sector point towards a relatively large value of
the reactor angle, incompatible with a vanishing theta_ 13 at about 3 sigma. In
order to explain such a result, we propose a SUSY model based on the broken
L_e-L_mu-L_tau symmetry, where large deviations from the symmetric limit
theta_12 = pi/4, tan(theta_23) \sim O(1) and theta_13 = 0 mainly come from the
charged lepton sector. We show that a description of all neutrino data is
possible if the charged lepton mass matrix has a special pattern of complex
matrix elements.Comment: 9 pages, 2 figures. v2: comments and references added, as published
in JHE
Fine-tuning and naturalness issues in the two-zero neutrino mass textures
In this paper we analyze the compatibility of two-zero neutrino Majorana
textures with the recent experimental data. Differently from previous works, we
use the experimental data to fix the values of the non-vanishing mass matrix
entries and study in detail the correlations and degree of fine-tuning among
them, which is also a measure of how naturally a given texture is able to
describe all neutrino data. This information is then used to expand the
textures in powers of the Cabibbo angle; extracting random O(1) coefficients,
we show that only in few cases such textures reproduce the mixing parameters in
their 3 sigma ranges.Comment: 13 pages, 14 figures. Version to appear in NP
Repressing Anarchy in Neutrino Mass Textures
The recent results that is relatively large, of the order of
the previous upper bound, and the indications of a sizable deviation of
from the maximal value are in agreement with the predictions of
Anarchy in the lepton sector. The quark and charged lepton hierarchies can then
be reproduced in a SU(5) GUT context by attributing non-vanishing
charges, different for each family, only to the SU(5) tenplet states. The fact
that the observed mass hierarchies are stronger for up quarks than for down
quarks and charged leptons supports this idea. As discussed in the past, in the
flexible context of , different patterns of charges can
be adopted going from Anarchy to various types of hierarchy. We revisit this
approach by also considering new models and we compare all versions to the
present data. As a result we confirm that, by relaxing the extreme ansatz of
equal charges for all SU(5) pentaplets and singlets, better
agreement with the data than for Anarchy is obtained without increasing the
model complexity. We also present the distributions obtained in the different
models for the Dirac CP-violating phase. Finally we discuss the relative merits
of these simple models.Comment: v1: 12 pages, 3 figures; v2: 13 pages, 3 figures, text improved,
matches version accepted for publication; v3: submitted to add an
acknowledgment to a networ
Discrete symmetries and models of flavor mixing
Evidences of a discrete symmetry behind the pattern of lepton mixing are
analyzed. The program of "symmetry building" is outlined. Generic features and
problems of realization of this program in consistent gauge models are
formulated. The key issues include the flavor symmetry breaking, connection of
mixing and masses, {\it ad hoc} prescription of flavor charges, "missing"
representations, existence of new particles, possible accidental character of
the TBM mixing. Various ways are considered to extend the leptonic symmetries
to the quark sector and to reconcile them with Grand Unification. In this
connection the quark-lepton complementarity could be a viable alternative to
TBM. Observational consequences of the symmetries and future experimental tests
of their existence are discussed.Comment: 14 pages, 5 figures. Talk given at the Symposium "DISCRETE 2010", 6 -
11 December 2010, La Sapienza, Rome, Ital
Accidental stability of dark matter
We propose that dark matter is stable as a consequence of an accidental Z2
that results from a flavour-symmetry group which is the double-cover group of
the symmetry group of one of the regular geometric solids. Although
model-dependent, the phenomenology resembles that of a generic Higgs portal
dark matter scheme.Comment: 12 pages, final version, published in JHE
A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing
We present a see-saw model for Tri-Bimaximal mixing which is based on a
very economical flavour symmetry and field content and still possesses all the
good features of models. In particular the charged lepton mass
hierarchies are determined by the flavour symmetry itself
without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is
exact in leading order while all the mixing angles receive corrections of the
same order in next-to-the-leading approximation. As a consequence the predicted
value of is within the sensitivity of the experiments which will
take data in the near future. The light neutrino spectrum, typical of
see-saw models, with its phenomenological implications, also including
leptoproduction, is studied in detail.Comment: 20 pages, 2 figure
A See-Saw model for fermion masses and mixings
We present a supersymmetric see-saw model giving rise to the most
general neutrino mass matrix compatible with Tri-Bimaximal mixing. We adopt the
flavour symmetry, broken by suitable vacuum expectation values
of a small number of flavon fields. We show that the vacuum alignment is a
natural solution of the most general superpotential allowed by the flavour
symmetry, without introducing any soft breaking terms. In the charged lepton
sector, mass hierarchies are controlled by the spontaneous breaking of the
flavour symmetry caused by the vevs of one doublet and one triplet flavon
fields instead of using the Froggatt-Nielsen U(1) mechanism. The next to
leading order corrections to both charged lepton mass matrix and flavon vevs
generate corrections to the mixing angles as large as .
Applied to the quark sector, the symmetry group can give a
leading order proportional to the identity as well as a matrix with
coefficients in the Cabibbo submatrix. Higher order
corrections produce non vanishing entries in the other entries which
are generically of .Comment: 30 pages, 3 figures, minor changes to match the published versio
Discrete Flavour Groups, \theta_13 and Lepton Flavour Violation
Discrete flavour groups have been studied in connection with special patterns
of neutrino mixing suggested by the data, such as Tri-Bimaximal mixing (groups
A4, S4...) or Bi-Maximal mixing (group S4...) etc. We review the predictions
for sin(\theta_13) in a number of these models and confront them with the
experimental measurements. We compare the performances of the different classes
of models in this respect. We then consider, in a supersymmetric framework, the
important implications of these flavour symmetries on lepton flavour violating
processes, like \mu -> e gamma and similar processes. We discuss how the
existing limits constrain these models, once their parameters are adjusted so
as to optimize the agreement with the measured values of the mixing angles. In
the simplified CMSSM context, adopted here just for indicative purposes, the
small tan(beta) range and heavy SUSY mass scales are favoured by lepton flavour
violating processes, which makes it even more difficult to reproduce the
reported muon g-2 discrepancy.Comment: 45 pages, 16 figures, 3 tables; V3 submitted to add an acknowledgment
to a Networ
Towards Minimal S4 Lepton Flavor Model
We study lepton flavor models with the flavor symmetry. We construct
simple models with smaller numbers of flavon fields and free parameters, such
that we have predictions among lepton masses and mixing angles. The model with
a triplet flavon is not realistic, but we can construct realistic models
with two triplet flavons, or one triplet and one doublet flavons.Comment: 18 pages, 4 figures, references are adde
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