178 research outputs found
Possible Flavor Mixing Structures of Lepton Mass Matrices
To search for possible textures of lepton mass matrices, we systematically
examine flavor mixing structures which can lead to large lepton mixing angles.
We find out 37 mixing patterns are consistent with experimental data, taking
into account phase factors in the mixing matrices. Only six of the patterns can
explain the observed data without any tuning of parameters, while the others
need particular choices for the phase values. It is found that these six mixing
patterns are those predicted by the models which have been proposed to account
for fermion mass hierarchies. On the other hand, the others may give new flavor
mixing structures of lepton mass matrices and therefore new possibilities of
model construction.Comment: 21 page
Relating large to the ratio of neutrino mass-squared differences
The non-zero and sizable value of puts pressure on flavor symmetry
models which predict an initially vanishing value. Hence, the tradition of
relating fermion mixing matrix elements with fermion mass ratios might need to
be resurrected. We note that the recently observed non-vanishing value of
can be related numerically to the ratio of solar and atmospheric
mass-squared differences. The most straightforward realization of this can be
achieved with a combination of texture zeros and a vanishing neutrino mass. We
analyze the implications of some of these possibilities and construct explicit
flavor symmetry models that predict these features.Comment: 13 pages, 2 figure
Neutrino Large Mixing in Universal Yukawa Coupling Model with Small Violation
We have analyzed the possibility that the universal Yukawa coupling
(democratic mass matrix) with small violations of Dirac and Majorana neutrinos
can induce the large mixing of neutrinos through the seesaw mechanism. The
possibility can be achieved by the condition that the violation parameters of
Majorana neutrinos are sufficiently smaller than the violation parameters of
Dirac neutrinos. Allowed regions of the violation parameters producing the
observed neutrino mass hierarchy and large neutrino mixing are not so
restricted at present in contrast to the violation parameters for quark sector.Comment: 14 pages, 4figure
Cancellations in Neutrinoless Double Beta Decay and the Neutrino Mass Matrix
In a degenerate scheme with mass m_0 a complete analysis of the allowed range
of the effective electron neutrino Majorana mass is performed. Special
attention is paid to effects of cancellations caused either by intrinsic CP
parities of the eigenstates (CP invariance) or by complex mixing matrix
elements (CP violation). We investigate all possibilities and give in each case
constraints on the phases, the relative CP parities or the neutrino mass scale.
A solar mixing angle \sin^2 2 \theta smaller than 0.7 jeopardizes the
degenerate mass scheme. A key value of /m_0 is identified, which is
independent on the solar solution and would rule out certain schemes. Also it
would answer the question regarding the presence of CP violation. Even if a
total neutrino mass scale and an effective mass is measured, the value of the
phases or parities is not fixed, unless in some special cases. The resulting
uncertainty in the other mass matrix elements is at least of the same order
than the one stemming from nuclear matrix elements calculations.Comment: 20 pages, 10 figures. Title, abstract and parts of the text change
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
Zee model and phenomenology of lepton sector
The virtual effects of the Zee charged scalar boson on the
lepton-family-number (LFN) violating processes are studied. We obtain the
constraints on the individual Yukawa coupling constants of the Zee boson to
leptons. Using these constraints, we predict the upper bounds on the
muonium-antimuonium conversion probability, the branching fractions of the LFN
violating decays such as , , and . The contribution of the Zee boson to
the muon anomalous magnetic moment is also consideredComment: 13pages, 2figures, Latex; Notes added, two references adde
Breaking Tri-bimaximal Mixing and Large
The long baseline neutrino experiment, T2K, and the reactor experiment,
Double Chooz will soon present new data. If we expect to be
0.1-0.2, which is close to the present experimental upper bound, we should not
persist in the paradigm of the tri-bimaximal mixing. We discuss breaking the
tri-bimaximal mixing by adding a simple mass matrix, which could be derived
from some non-Abelian discrete symmetries. It is found that
is expected in our model independent analysis of the
generalized mass matrix for the normal or inverted hierarchical neutrino mass
spectrum. On the other hand, and are
expected to be not far from 1/2 and 1/3, respectively. As a typical example, we
also discuss the flavor model with the 1 and 1' flavons, which break the
tri-bimaximal mixing considerably. In this modified version of the Altarelli
and Feruglio model, is predicted to be around 0.15 in the
case of the normal hierarchical neutrino masses , and 0.2 in
the case of the inverted hierarchy . The form of the neutrino
mass matrix looks rather interesting --- it is suggestive of other discrete
symmetries as well.Comment: 10 pages, 12 figures, final versio
Neutrino masses and mixing with seesaw mechanism and universal breaking of extended democracy
In the framework of a minimal extension of the SM, where the only additional
fields are three right-handed neutrinos, we suggest that the charged lepton,
the Dirac neutrino and the right-handed Majorana neutrino mass matrices are
all, to leading approximation, proportional to the democratic matrix. With the
further assumption that the breaking of this extended democracy is universal
for all leptonic mass matrices, a large mixing in the 2-3 sector can be
obtained and is linked to the seesaw mechanism, together with the existence of
a strong hierarchy in the masses of right-handed neutrinos. The structure of
the resulting effective mass matrix of light neutrinos is stable against the
RGE evolution, and a good fit to all solar and atmospheric neutrino data is
obtained.Comment: LaTeX, 17 pages, 2 eps figures. A section on RGE evolution and a few
references added; minor typos correcte
Minimal Modification To The Tri-bimaximal Neutrino Mixing
Current experimental data on neutrino oscillations are consistent with the
tri-bimaximal mixing. If future experimental data will determine a non-zero
and/or find CP violations in neutrino oscillations, there is the need
to modify the mixing pattern. We find that a simple neutrino mass matrix,
resulting from family symmetry breaking with residual and
discrete symmetries respectively for the Higgs sectors generating the charged
lepton and neutrino mass matrices, can satisfy the required modifications. The
neutrino mass matrix is minimally modified with just one additional complex
parameter compared with the one producing the tri-bimaximal mixing. In this
case, the CP violating Jarlskog factor has a simple form
( for real neutrino mass matrix), and also
. We also discuss how this mixing matrix can be tested
experimentally.Comment: Latex 11 pages with no figures. References adde
Neutrinos Have Mass - So What?
In this brief review, I discuss the new physics unveiled by neutrino
oscillation experiments over the past several years, and discuss several
attempts at understanding the mechanism behind neutrino masses and lepton
mixing. It is fair to say that, while significant theoretical progress has been
made, we are yet to construct a coherent picture that naturally explains
non-zero, yet tiny, neutrino masses and the newly revealed, puzzling patterns
of lepton mixing. I discuss what the challenges are, and point to the fact that
more experimental input (from both neutrino and non-neutrino experiments) is
dearly required - and that new data is expected to reveal, in the next several
years, new information. Finally, I draw attention to the fact that neutrinos
may have only just begun to reshape fundamental physics, given the fact that we
are still to explain the LSND anomaly and because the neutrino oscillation
phenomenon is ultimately sensitive to very small new-physics effects.Comment: invited brief review, 15 pages, 1 eps figure, typo corrected,
reference adde
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