542 research outputs found
Neutrino Mass Patterns within the See-saw Model from Multi-localization along Extra Dimensions
We study a multi-localization model for charged leptons and neutrinos,
including the possibility of a see-saw mechanism. This framework offers the
opportunity to allow for realistic solutions in a consistent model without
fine-tuning of parameters, even if quarks are also considered. Those solutions
predict that the large Majorana mass eigenvalues for right-handed neutrinos are
of the same order of magnitude, although this almost common mass can span a
large range (bounded from above by ). The model also
predicts Majorana masses between and $\sim 5 \
10^{-2}{\rm eV}\beta\theta_{13}10^{-2} \lesssim
\sin \theta_{13} \lesssim 10^{-1}$, but smaller values are not totally excluded
by the model.Comment: 36 pages, 8 figure
Heavy-meson physics and flavour violation with a single generation
We study flavour-violating processes which involve heavy B- and D-mesons and
are mediated by Kaluza-Klein modes of gauge bosons in a previously suggested
model where three generations of the Standard Model fermions originate from a
single generation in six dimensions. We find the bound on the size R of the
extra spatial dimensions 1/R>3.3 TeV, which arises from the three-body decay
B_s to K mu e. Due to the still too low statistics this bound is much less
stringent than the constraint arising from K to mu e, 1/R>64 TeV, which was
found in a previous work (Frere et al., JHEP, 2003). Nevertheless, we argue
that a clear signature of the model would be an observation of K to mu e and
B_s to K mu e decays without observations of other flavour and lepton number
changing processes at the same precision level.Comment: 15 page
Towards Z_2-protected gauge--Higgs unification
In theories with flux compactification in eight or higher dimensions, the
extra-dimensional components of the gauge field may be regarded as the Higgs
field candidates. We suggest a way to protect these components from getting
large tree-level masses by imposing a -symmetry acting on compact
manifolds and background fields on them. In our scheme the infinite series of
heavy KK modes naturally decouples from the light Higgs candidates, whose
number is generically larger than one. We also present toy models with three
families of leptons, illustrating that the Yukawa sector in our scheme is
fairly strongly constrained. In one of these models, one fermion gets a
tree-level mass after electroweak symmetry breaking, while two others remain
naturally massless at the tree level.Comment: A few points clarified. Journal versio
Contrasting patterns of selection between MHC I and II across populations of Humboldt and Magellanic penguins
Indexación: Web of ScienceThe evolutionary and adaptive potential of populations or species facing an emerging infectious disease depends on their genetic diversity in genes, such as the major histocompatibility complex (MHC). In birds, MHC class I deals predominantly with intracellular infections (e.g., viruses) and MHC class II with extracellular infections (e.g., bacteria). Therefore, patterns of MHC I and II diversity may differ between species and across populations of species depending on the relative effect of local and global environmental selective pressures, genetic drift, and gene flow. We hypothesize that high gene flow among populations of Humboldt and Magellanic penguins limits local adaptation in MHC I and MHC II, and signatures of selection differ between markers, locations, and species. We evaluated the MHC I and II diversity using 454 next-generation sequencing of 100 Humboldt and 75 Magellanic penguins from seven different breeding colonies. Higher genetic diversity was observed in MHC I than MHC II for both species, explained by more than one MHC I loci identified. Large population sizes, high gene flow, and/or similar selection pressures maintain diversity but limit local adaptation in MHC I. A pattern of isolation by distance was observed for MHC II for Humboldt penguin suggesting local adaptation, mainly on the northernmost studied locality. Furthermore, trans species alleles were found due to a recent speciation for the genus or convergent evolution. High MHC I and MHC II gene diversity described is extremely advantageous for the long term survival of the species.http://onlinelibrary.wiley.com/doi/10.1002/ece3.2502/epd
Searching for family-number conserving neutral gauge bosons from extra dimensions
Previous studies have shown how the three generations of the Standard Model
fermions can arise from a single generation in more than four dimensions, and
how off-diagonal neutral couplings arise for gauge-boson Kaluza-Klein
recurrences. These couplings conserve family number in the leading
approximation. While an existing example, built on a spherical geometry,
suggests a high compactification scale, we conjecture that the overall
structure is generic, and work out possible signatures at colliders, compatible
with rare decays data.Comment: 4 pages, 2 figures, jetpl.cls style, references adde
See-saw neutrino masses and large mixing angles in the vortex background on a sphere
In the vortex background on a sphere, a single 6-dimensional fermion family
gives rise to 3 zero-modes in the 4-dimensional point of view, which may
explain the replication of families in the Standard Model. Previously, it had
been shown that realistic hierarchical mass and mixing patterns can be
reproduced for the quarks and the charged leptons. Here, we show that the
addition of a single heavy 6-dimensional field that is gauge singlet, unbound
to the vortex, and embedded with a bulk Majorana mass enables to generate 4D
Majorana masses for the light neutrinos through the see-saw mechanism. The
scheme is very predictive. The hierarchical structure of the fermion zero-modes
leads automatically to an inverted pseudo-Dirac mass pattern, and always
predicts one maximal angle in the neutrino see-saw matrix. It is possible to
obtain a second large mixing angle from either the charged lepton or the
neutrino sector, and we demonstrate that this model can fit all observed data
in neutrino oscillations experiments. Also, U_{e3} is found to be of the order
~0.1.Comment: 23 pages, 1 figur
Prevalence of blaSHV genes in clinical isolates of Klebsiella pneumoniae at Saint Camille medical Center in Ouagadougou. Isolation of blaSHV11-like gene
Five bacterial strains (4 Klebsiella pneumoniae and 1 Escherichia coli) representative of pathogenic species and resistant to β-lactam antibiotics are investigated to isolate the genes responsible of β--lactamase activity. The use of engineering techniques enables us to show the widespread of blaSHV genes particularly in clinical isolates of K. pneumoniae. Our results highlighted an atypical blaSHV-11 gene.
Key words: β--Lactamases, Klebsiella pneuminiae, blaSHV gene, Saint Camille medical centre, Ouagadougou.
African Journal of Biotechnology Vol.3(9) 2004: 477-48
Chiral Compactification on a Square
We study quantum field theory in six dimensions with two of them compactified
on a square. A simple boundary condition is the identification of two pairs of
adjacent sides of the square such that the values of a field at two identified
points differ by an arbitrary phase. This allows a chiral fermion content for
the four-dimensional theory obtained after integrating over the square. We find
that nontrivial solutions for the field equations exist only when the phase is
a multiple of \pi/2, so that this compactification turns out to be equivalent
to a T^2/Z_4 orbifold associated with toroidal boundary conditions that are
either periodic or anti-periodic. The equality of the Lagrangian densities at
the identified points in conjunction with six-dimensional Lorentz invariance
leads to an exact Z_8\times Z_2 symmetry, where the Z_2 parity ensures the
stability of the lightest Kaluza-Klein particle.Comment: 28 pages, latex. References added. Clarifying remarks included in
section 2. Minor corrections made in section
FCNC in left-right symmetric theories and constraints on the right-handed scale
We revise the limits on the FCNC higgses in manifestly left-right symmetric
theories. It is shown that the combination of the Kobayashi-Maskawa
CP-violation with the tree level higgs exchange gives very large
contribution to the CP-violating parameter. It leads to the new
strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of
the order . Being addressed to the supersymmetric left-right
models, FCNC problem requires both right-handed scale and supersymmetric mass
parameters be heavier than 50 TeV for . The most relaxed case
corresponds to where right-handed scale can be of the
order of few TeV.Comment: 11 pages, latex, 3 figure
Are the New Physics Contributions from the Left-Right Symmetric Model Important for the Indirect CP Violation in the Neutral B Mesons?
Several works analyzing the new physics contributions from the Left-Right
Symmetric Model to the CP violation phenomena in the neutral B mesons can be
found in the literature. These works exhibit interesting and experimentally
sensible deviations from the Standard Model predictions but at the expense of
considering a low right scale \upsilon_R around 1 TeV. However, when we stick
to the more conservative estimates for \upsilon_R which say that it must be at
least 10^7 GeV, no experimentally sensible deviations from the Standard Model
appear for indirect CP violation. This estimate for \upsilon_R arises when the
generation of neutrino masses is considered. In spite of the fact that this
scenario is much less interesting and says nothing new about both the CP
violation phenomenon and the structure of the Left-Right Symmetric Model, this
possibility must be taken into account for the sake of completeness and when
considering the see-saw mechanism that provides masses to the neutrino sector.Comment: LaTex file. 19 pages, 4 figures. Change in the way the paper address
the problem. As a result, change in title, abstract, and some sections.
Conclusions unchanged. Version to appear in Foundations of Physics Letter
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