266 research outputs found
Can the Zee Model Explain the Observed Neutrino Data?
The eigenvalues and mixing angles in the Zee model are investigated
parameter-independently. When we require |\Delta m^2_{12}/\Delta m^2_{23}| \ll
1 in order to understand the solar and atmospheric data simultaneously, the
only solution is one which gives bi-maximal mixing. It is pointed out that the
observed values \sin^2 2\theta_{solar} \simeq 0.66 in the MSW LMA solution
cannot be explained within the framework of the Zee model, because we derive a
severe constraint on the value of \sin^2 2 \theta_{solar}, \sin^2 2
\theta_{solar} \geq 1 -(1/16)(\Delta m^2_{solar}/\Delta m^2_{atm})^2.Comment: Latex file, 10 pages, 1 figure, explanations and references added,
typos corrected, to be published in Phys.Rev.
Escape from washing out of baryon number in a two-zero-texture general Zee model compatible with the large mixing angle MSW solution
We propose a two-zero-texture general Zee model, compatible with the large
mixing angle Mikheyev-Smirnov-Wolfenstein solution. The washing out of the
baryon number does not occur in this model for an adequate parameter range. We
check the consistency of a model with the constraints coming from flavor
changing neutral current processes, the recent cosmic microwave background
observation, and the Z-burst scenario.Comment: 22 pages, 2 eps figures, Type set revtex
Deviation from tri-bimaximal mixings in two types of inverted hierarchical neutrino mass models
An attempt is made to explore the possibility for deviations of solar mixing
angle () from tri-bimaximal mixings, without sacrificing the
predictions of maximal atmospheric mixing angle () and zero
reactor angle (). We find that the above conjecture can be
automatically realised in the inverted hierarchical neutrino mass model having
2-3 symmetry, in the basis where charged lepton mass matrix is diagonal. For
the observed ranges of and \bigtriangleup m^2_{23],
we calculate the predictions on for
different input values of the parameters in the neutrino mass matrix. We also
observe a possible crossing over from one type of inverted hierarchical model
having same CP parity (Type-IHA) to other type having opposite CP parity
(Type-IHB). Such neutrino mass matrices can be obtained from the canonical
seesaw formula using diagonal form of Dirac neutrino mass matrix and
non-diagonal texture of right-handed Majorana mass matrix, and may have
important implications in model building using discrete as well as non-abelian
symmetry groups.Comment: 13 pages, 7 figure
Bilarge Neutrino Mixing and \mu - \tau Permutation Symmetry for Two-loop Radiative Mechanism
The presence of approximate electron number conservation and \mu-\tau
permutation symmetry of S_2 is shown to naturally provide bilarge neutrino
mixing. First, the bimaximal neutrino mixing together with U_{e3}=0 is
guaranteed to appear owing to S_2 and, then, the bilarge neutrino mixing
together with |U_{e3}|<<1 arises as a result of tiny violation of S_2. The
observed mass hierarchy of \Delta m^2_{\odot}<<\Delta m^2_{atm} is subject to
another tiny violation of the electron number conservation. This scenario is
realized in a specific model based on SU(3)_L x U(1)_N with two-loop radiative
mechanism for neutrino masses. The radiative effects from heavy leptons
contained in lepton triplets generate the bimaximal structure and those from
charged leptons, which break S_2, generate the bilarge structure together with
|U_{e3}|<<1. To suppress dangerous flavor-changing neutral current interactions
due to Higgs exchanges especially for quarks, this S_2 symmetry is extended to
a discrete Z_8 symmetry, which also ensures the absence of one-loop radiative
mechanism.Comment: 18 pages, 7 figures, to appear in Phys. Rev.
Lepton Masses from a TeV Scale in a 3-3-1 Model
In this work, using the fact that in 3-3-1 models the same leptonic bilinear
contributes to the masses of both charged leptons and neutrinos, we develop an
effective operator mechanism to generate mass for all leptons. The effective
operators have dimension five for the case of charged leptons and dimension
seven for neutrinos. By adding extra scalar multiplets and imposing the
discrete symmetry we are able to generate realistic textures
for the leptonic mixing matrix. This mechanism requires new physics at the TeV
scale.Comment: RevTex, 13 pages. Extended version to be published in Physical Review
Two-loop Radiative Neutrino Mechanism in an Gauge Model
By using the - - symmetry, we construct an
gauge model that provides two-loop radiative neutrino
masses as well as one-loop radiative neutrino masses. The generic smallness of
two-loop neutrino masses leading to compared with one-loop
neutrino masses leading to successfully explains by invoking the - -
breaking. The Higgs scalar () that initiates radiative mechanisms is
unified into a Higgs triplet together with the standard Higgs scalar (,
) to form (, , ), which calls for three families
of lepton triplets: (, , ) (i = 1,2,3), where
denote heavy neutral leptons. The two-loop radiative mechanism is
found possible by introducing a singly charged scalar, which couples to
(i,j = 2,3).Comment: with 10 pages, revtex, including 2 figures, accepted for publication
in Phys. Rev. D (with undefined latex citation indices removed
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
Constraints On Radiative Neutrino Mass Models From Oscillation Data
The three neutrino Zee model and its extension including three active and one
sterile species are studied in the light of new neutrino oscillation data. We
obtain analytical relations for the mixing angle in solar oscillations in terms
of neutrino mass squared differences. For the four neutrino case, we obtain the
result , which can accommodate both the large
and small mixing scenarios. We show that within this framework, while both the
SMA-MSW and the LMA-MSW solutions can easily be accommodated, it would be
difficult to reconcile the LOW-QVO solutions. We also comment on the
active-sterile admixture within phenomenologically viable textures.Comment: The paper has been substantially rewritten, especially in Section IV,
though the basic results are unchanged. Some new references and an appendix
have been adde
Almost Maximal Lepton Mixing with Large T Violation in Neutrino Oscillations and Neutrinoless Double Beta Decay
We point out two simple but instructive possibilities to construct the
charged lepton and neutrino mass matrices, from which the nearly bi-maximal
neutrino mixing with large T violation can naturally emerge. The two lepton
mixing scenarios are compatible very well with current experimental data on
solar and atmospheric neutrino oscillations, and one of them may lead to an
observable T-violating asymmetry between \nu_\mu --> \nu_e and \nu_e -->
\nu_\mu transitions in the long-baseline neutrino oscillation experiments.
Their implications on the neutrinoless double beta decay are also discussed.Comment: RevTex 15 pages (2 PS figures
A texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande
(SK), CHOOZ and neutrinoless double beta decay , we
consider a texture of neutrino mass matrix which contains three parameters in
order to explain those neutrino experimental results. We have first fitted
parameters in a model independent way with solar and atmospheric neutrino mass
squared differences and solar neutrino mixing angle which satisfy LMA solution.
The maximal value of atmospheric neutrino mixing angle comes out naturally in
the present texture. Most interestingly, fitted parameters of the neutrino mass
matrix considered here also marginally satisfy recent limit on effective
Majorana neutrino mass obtained from neutrinoless double beta decay experiment.
We further demonstrate an explicit model which gives rise to the texture
investigated by considering an gauge group with two
extra real scalar singlets and discrete symmetry. Majorana
neutrino masses are generated through higher dimensional operators at the scale
. We have estimated the scales at which singlets get VEV's and M by
comparing with the best fitted results obtained in the present work.Comment: Journal Ref.: Phys. Rev. D66, 053004 (2002
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