496 research outputs found
A new mechanism for a naturally small Dirac neutrino mass
A mechanism is proposed in which a right-handed neutrino zero mode and a
right-handed charged lepton zero mode can be localized at the same place along
an extra compact dimension while having markedly different spreads in their
wave functions: a relatively narrow one for the neutrino and a rather broad one
for the charged lepton. In their overlaps with the wave function for the
left-handed zero modes, this mechanism could produce a natural large hierarchy
in the effective Yukawa couplings in four dimensions, and hence a large
disparity in masses.Comment: 6 pages (2 with figures), twocolumn forma
Large Mixing Induced by the Strong Coupling with a Single Bulk Neutrinos
Neutrino is a good probe of extra dimensions. Large mixing and the apparent
lack of very complicated oscillation patterns may be an indication of large
couplings between the brane and a single bulk neutrino. A simple and realistic
five-dimensional model of this kind is discussed. It requires a sterile in
addition to three active neutrinos on the brane, all coupled strongly to one
common bulk neutrino, but not directly among themselves. Mindful that sterile
neutrinos are disfavored in the atmospheric and solar data, we demand induced
mixing to occur among the active neutrinos, but not between the active and the
sterile. The size of the extra dimension is arbitrary in this model,
otherwise it contains six parameters which can be used to fit the three
neutrino masses and the three mixing angles. However, in the model those six
parameters must be suitably ordered, so a successful fit is not guaranteed. It
turns out that not only the data can be fitted, but as a result of the
ordering, a natural connection between the smallness of the reactor angle
and the smallness of the mass-gap ratio can be derived.Comment: Misprints above eq. (22) corrected. To appear in PR
Lepton Masses and Mixing in a Left-Right Symmetric Model with a TeV-scale Gravity
We construct a left-right symmetric (LRS) model in five dimensions which
accounts naturally for the lepton flavor parameters. The fifth dimension is
described by an orbifold, S_1/Z_2 times Z'_2, with a typical size of order
TeV^{-1}. The fundamental scale is of order 25 TeV which implies that the gauge
hierarchy problem is ameliorated. In addition the LRS breaking scale is of
order few TeV which implies that interactions beyond those of the standard
model are accessible to near future experiments. Leptons of different
representations are localized around different orbifold fixed points. This
explains, through the Arkani-Hamed-Schmaltz mechanism, the smallness of the tau
mass compared to the electroweak breaking scale. An additional U(1) horizontal
symmetry, broken by small parameters, yields the hierarchy in the charged
lepton masses, strong suppression of the light neutrino masses and accounts for
the mixing parameters. The model yields several unique predictions. In
particular, the branching ratio for the lepton flavor violating process mu^-
--> e^+ e^- e^- is comparable with its present experimental sensitivity.Comment: 21 pages, 1 figure, references added, discussion on the
predictiveness of the model in the generic non-universal case added, to
appear in PR
The Majorana Neutrino Mass Matrix with One Texture Zero and One Vanishing Eigenvalue
Possible patterns of the Majorana neutrino mass matrix with one texture
zero and one vanishing eigenvalue are classified and discussed. We find that
three one-zero textures of with and four one-zero textures of
with are compatible with current neutrino oscillation data. The
implications of these phenomenological anstze on the neutrino mass
spectrum and the neutrinoless double beta decay are also explored in some
detail.Comment: RevTex 10 pages (with 2 PS figues). More discussions and references
adde
On Neutrino Masses and a Low Breaking Scale of Left-Right Symmetry
In left-right symmetric models (LRSM) the light neutrino masses arise from
two sources: the seesaw mechanism and a VEV of an SU(2) triplet. If the
left-right symmetry breaking, , is low, v_R\lsim15\TeV, the
contributions to the light neutrino masses from both the seesaw mechanism and
the triplet Yukawa couplings are expected to be well above the experimental
bounds. We present a minimal LRSM with an additional U(1) symmetry in which the
masses induced by the two sources are below the eV scale and the two-fold
problem is solved. We further show that, if the U(1) symmetry is also
responsible for the lepton flavor structure, the model yields a small mixing
angle within the first two lepton generations.Comment: 18 pages references added published versio
A Model for Neutrino Masses and Dark Matter
We propose a model for neutrino masses that simultaneously results in a new
dark matter candidate, the right-handed neutrino. We derive the dark matter
abundance in this model, show how the hierarchy of neutrino masses is obtained,
and verify that the model is compatible with existing experimental results. The
model provides an economical method of unifying two seemingly separate puzzles
in contemporary particle physics and cosmology.Comment: 4 pages, submitted to PR
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
Body Mass Index (BMI) Effect on Galvanic Coupling Intra-Body Communication
Intra-body communication (IBC) is a wireless communication system where human body is used as a signal transmission medium. Main advantage of IBC compared to other wireless communication is capable of low power consumption. There are two coupling methods in IBC, which are capacitive and galvanic coupling. The characteristic of human body play an important role in IBC because the transmitted signal is propagates through the body tissue. Therefore, this paper investigates the effect of different dielectric properties of body tissues to the quality of IBC signal transmission by focusing at body fat. Galvanic coupling method was used. 12 subjects were volunteered in this study and the value of subject’s body fat was differentiates by body mass index (BMI). The frequency was focused on 21 MHz, 50 MHz and 80 MHz. The signal quality at 21 MHz and 80 MHz shows the degradation as the increasing of body fat. The signal attenuation is increasing as body fat increased because in human body, the bone and fat has higher resistance than nerves and muscle. However, at frequency 50 MHz, the increasing of human BMI does not increase the attenuation where the attenuations are at peak value
The SUSY seesaw model and lepton-flavor violation at a future electron-positron linear collider
We study lepton-flavor violating slepton production and decay at a future
e^+e^- linear collider in context with the seesaw mechanism in mSUGRA post-LEP
benchmark scenarios. The present knowledge in the neutrino sector as well as
improved future measurements are taken into account. We calculate the signal
cross-sections \sigma(e^{+/-}e^- -> l_{\beta}^{+/-} l_{\alpha}^-
\tilde{\chi}_b^0 \tilde{\chi}_a^0); l_{\delta}=e, \mu, \tau; \alpha =|= \beta
and estimate the main background processes. Furthermore, we investigate the
correlations of these signals with the corresponding lepton-flavor violating
rare decays l_{\alpha} -> l_{\beta} \gamma. It is shown that these correlations
are relatively weakly affected by uncertainties in the neutrino data, but very
sensitive to the model parameters. Hence, they are particularly suited for
probing the origin of lepton-flavor violation.Comment: 31 pages, 10 figures, version published in Phys. Rev.
Leptogenesis and low energy observables in left-right symmetric models
In the context of left-right symmetric models we study the connection of
leptogenesis and low energy parameters such as neutrinoless double beta decay
and leptonic CP violation. Upon imposition of a unitarity constraint, the
neutrino parameters are significantly restricted and the Majorana phases are
determined within a narrow range, depending on the kind of solar solution. One
of the Majorana phases gets determined to a good accuracy and thereby the
second phase can be probed from the results of neutrinoless double beta decay
experiments. We examine the contributions of the solar and atmospheric mass
squared differences to the asymmetry and find that in general the solar scale
dominates. In order to let the atmospheric scale dominate, some finetuning
between one of the Majorana phases and the Dirac CP phase is required. In this
case, one of the Majorana phases is determined by the amount of CP violation in
oscillation experiments.Comment: 18 pages, 6 figures. Matches version to appear in PR
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