16,105 research outputs found
Lepton masses and mixings in orbifold models with three Higgs families
We analyse the phenomenological viability of heterotic Z(3) orbifolds with
two Wilson lines, which naturally predict three supersymmetric families of
matter and Higgs fields. Given that these models can accommodate realistic
scenarios for the quark sector avoiding potentially dangerous flavour-changing
neutral currents, we now address the leptonic sector, finding that viable
orbifold configurations can in principle be obtained. In particular,it is
possible to accomodate present data on charged lepton masses, while avoiding
conflict with lepton flavour-violating decays. Concerning the generation of
neutrino masses and mixings, we find that Z(3) orbifolds offer several
interesting possibilities.Comment: 28 pages, 11 figures. References adde
Irreversible processes and the accelerated-decelerated phases of the Universe
A model for the Universe is proposed where it is considered as a mixture of
scalar and matter fields. The particle production is due to an irreversible
transfer of energy from the gravitational field to the matter field and
represented by a non-equilibrium pressure. This model can simulate three
distinct periods of the Universe: (a) an accelerated epoch where the energy
density of the scalar field prevails over the matter field, (b) a past
decelerated period where the energy density of the matter field becomes more
predominant than the scalar energy density, and (c) a present acceleration
phase where the scalar energy density overcomes the energy density of the
matter field.Comment: 6 pages, 2 figures, to be published in Brazilian Journal of Physic
Mirror-assisted coherent backscattering from the Mollow sidebands
In front of a mirror, the radiation of weakly driven large disordered clouds
presents an interference fringe in the backward direction, on top of an
incoherent background. Although strongly driven atoms usually present little
coherent scattering, we here show that the mirror-assisted version can produce
high contrast fringes, for arbitrarily high saturation parameters. The contrast
of the fringes oscillates with the Rabi frequency of the atomic transition and
the distance between the mirror and the atoms, due to the coherent interference
between the carrier and the Mollow sidebands of the saturated resonant
fluorescence spectrum emitted by the atoms. The setup thus represents a
powerful platform to study the spectral properties of ensembles of correlated
scatterers
Melhoramento genetico de gado de leite: seleção de vacas e touros.
bitstream/item/103183/1/CT-43-Melhoram-gen-gado-de-leite.pd
FCNCs in supersymmetric multi-Higgs doublet models
We conduct a general discussion of supersymmetric models with three families
in the Higgs sector. We analyse the scalar potential, and investigate the
minima conditions, deriving the mass matrices for the scalar, pseudoscalar and
charged states. Depending on the Yukawa couplings and the Higgs spectrum, the
model might allow the occurrence of potentially dangerous flavour changing
neutral currents at the tree-level. We compute model-independent contributions
for several observables, and as an example we apply this general analysis to a
specific model of quark-Higgs interactions, discussing how compatibility with
current experimental data constrains the Higgs sector.Comment: 30 pages, 9 figures. Comments and references added. Final version
published in Physical Review
Linear Theory of Electron-Plasma Waves at Arbitrary Collisionality
The dynamics of electron-plasma waves are described at arbitrary
collisionality by considering the full Coulomb collision operator. The
description is based on a Hermite-Laguerre decomposition of the velocity
dependence of the electron distribution function. The damping rate, frequency,
and eigenmode spectrum of electron-plasma waves are found as functions of the
collision frequency and wavelength. A comparison is made between the
collisionless Landau damping limit, the Lenard-Bernstein and Dougherty
collision operators, and the electron-ion collision operator, finding large
deviations in the damping rates and eigenmode spectra. A purely damped entropy
mode, characteristic of a plasma where pitch-angle scattering effects are
dominant with respect to collisionless effects, is shown to emerge numerically,
and its dispersion relation is analytically derived. It is shown that such a
mode is absent when simplified collision operators are used, and that
like-particle collisions strongly influence the damping rate of the entropy
mode.Comment: 23 pages, 10 figures, accepted for publication on Journal of Plasma
Physic
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