1,913 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
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
Nonlinear field theories during homogeneous spatial dilation
The effect of a uniform dilation of space on stochastically driven nonlinear
field theories is examined. This theoretical question serves as a model problem
for examining the properties of nonlinear field theories embedded in expanding
Euclidean Friedmann-Lema\^{\i}tre-Robertson-Walker metrics in the context of
cosmology, as well as different systems in the disciplines of statistical
mechanics and condensed matter physics. Field theories are characterized by the
speed at which they propagate correlations within themselves. We show that for
linear field theories correlations stop propagating if and only if the speed at
which the space dilates is higher than the speed at which correlations
propagate. The situation is in general different for nonlinear field theories.
In this case correlations might stop propagating even if the velocity at which
space dilates is lower than the velocity at which correlations propagate. In
particular, these results imply that it is not possible to characterize the
dynamics of a nonlinear field theory during homogeneous spatial dilation {\it a
priori}. We illustrate our findings with the nonlinear Kardar-Parisi-Zhang
equation
Visible in the laboratory and invisible in cosmology: decaying sterile neutrinos
The expansion history and thermal physical process that happened in the early
Universe before big bang nucleosynthesis (BBN) remains relatively unconstrained
by observations. Low reheating temperature universes with normalcy temperatures
of remain consistent with all observations,
and accommodate several new physics scenarios that would normally be
constrained by high-temperature reheating models, including massive sterile
neutrinos. We explore such scenarios' production of keV scale sterile neutrinos
and their resulting constraints from cosmological observations. The parameter
space for massive sterile neutrinos is much less constrained than in
high- thermal histories, though several cosmological constraints
remain. Such parameter space is the target of several current and upcoming
laboratory experiments such as TRISTAN (KATRIN), HUNTER, MAGNETO-, and
PTOLEMY. Cosmological constraints remain stringent for stable keV-scale sterile
neutrinos. However, we show that sterile neutrinos with a dark decay to
radiation through a or a new scalar are largely unconstrained by
cosmology. In addition, this mechanism of sterile neutrinos with large mixing
may provide a solution to the Hubble tension. We find that keV-scale sterile
neutrinos are therefore one of the best probes of the untested pre-BBN era in
the early Universe and could be seen in upcoming laboratory experiments.Comment: 9 pages, 3 figures, comments welcom
Phenomenological viability of orbifold models with three Higgs families
We discuss the phenomenological viability of string multi-Higgs doublet
models, namely a scenario of heterotic orbifolds with two Wilson lines,
which naturally predicts three supersymmetric families of matter and Higgs
fields. We study the orbifold parameter space, and discuss the compatibility of
the predicted Yukawa couplings with current experimental data. We address the
implications of tree-level flavour changing neutral processes in constraining
the Higgs sector of the model, finding that viable scenarios can be obtained
for a reasonably light Higgs spectrum. We also take into account the tree-level
contributions to indirect CP violation, showing that the experimental value of
can be accommodated in the present framework.Comment: 31 pages, 12 figures. Comments and references added. Final version to
be published in JHE
Classification of unitary highest weight representations for non compact real forms
Using Jakobsen theorems, unitarizability in Hermitian Symmetric Spaces is
discussed. The set of all missing highest weights is explicitly calculated and
the construction of their corresponding highest weights vectors is studied.Comment: PDF, 35 pages (late submission
Globular Clusters: DNA of Early-Type galaxies?
This paper explores if the mean properties of Early-Type Galaxies (ETG) can
be reconstructed from "genetic" information stored in their GCs (i.e., in their
chemical abundances, spatial distributions and ages). This approach implies
that the formation of each globular occurs in very massive stellar
environments, as suggested by some models that aim at explaining the presence
of multi-populations in these systems. The assumption that the relative number
of globular clusters to diffuse stellar mass depends exponentially on chemical
abundance, [Z/H], and the presence of two dominant GC sub-populations blue and
red, allows the mapping of low metallicity halos and of higher metallicity (and
more heterogeneous) bulges. In particular, the masses of the low-metallicity
halos seem to scale up with dark matter mass through a constant. We also find a
dependence of the globular cluster formation efficiency with the mean projected
stellar mass density of the galaxies within their effective radii. The analysis
is based on a selected sub-sample of galaxies observed within the ACS Virgo
Cluster Survey of the {\it Hubble Space Telescope}. These systems were grouped,
according to their absolute magnitudes, in order to define composite fiducial
galaxies and look for a quantitative connection with their (also composite)
globular clusters systems. The results strengthen the idea that globular
clusters are good quantitative tracers of both baryonic and dark matter in
ETGs.Comment: 20 pages, 28 figures and 5 table
Formación y desarrollo profesional del educador social en contextos de intervención [Reseña]
Sánchez Romero, C. (2014). Formación y desarrollo profesional del educador social en contextos de intervención. Madrid: UNED, 269 pp.
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