56,378 research outputs found
Exact self-duality in a modified Skyrme model
We propose a modification of the Skyrme model that supports a self-dual
sector possessing exact non-trivial finite energy solutions. The action of such
a theory possesses the usual quadratic and quartic terms in field derivatives,
but the couplings of the components of the Maurer-Cartan form of the Skyrme
model is made by a non-constant symmetric matrix, instead of the usual Killing
form of the SU(2) Lie algebra. The introduction of such a matrix make the
self-duality equations conformally invariant in three space dimensions, even
though it may break the global internal symmetries of the original Skyrme
model. For the case where that matrix is proportional to the identity we show
that the theory possesses exact self-dual Skyrmions of unity topological
charges.Comment: 12 pages, no figure
Texture-zero model for the lepton mass matrices
We suggest a simple model, based on the type-I seesaw mechanism, for the
lepton mass matrices. The model hinges on an Abelian symmetry which leads to
mass matrices with some vanishing matrix elements. The model predicts one
massless neutrino and ( is the effective light-neutrino
Majorana mass matrix). We show that these predictions perfectly agree with the
present experimental data if the neutrino mass spectrum is inverted, i.e. if
, provided the Dirac phase is very close to maximal (). In the case of a normal neutrino mass spectrum, i.e. when , the
agreement of our model with the data is less than optimal---the reactor mixing
angle is too small in our model. Minimal leptogenesis is not an
option in our model due to the vanishing elements in the Yukawa-coupling
matrices.Comment: 10 pages, 3 figures; version for journal: new fit to data, new plot
Exact Self-Dual Skyrmions
We introduce a Skyrme type model with the target space being the 3-sphere S^3
and with an action possessing, as usual, quadratic and quartic terms in field
derivatives. The novel character of the model is that the strength of the
couplings of those two terms are allowed to depend upon the space-time
coordinates. The model should therefore be interpreted as an effective theory,
such that those couplings correspond in fact to low energy expectation values
of fields belonging to a more fundamental theory at high energies. The theory
possesses a self-dual sector that saturates the Bogomolny bound leading to an
energy depending linearly on the topological charge. The self-duality equations
are conformally invariant in three space dimensions leading to a toroidal
ansatz and exact self-dual Skyrmion solutions. Those solutions are labelled by
two integers and, despite their toroidal character, the energy density is
spherically symmetric when those integers are equal and oblate or prolate
otherwise.Comment: 14 pages, 3 figures, a reference adde
Tau-functions and Dressing Transformations for Zero-Curvature Affine Integrable Equations
The solutions of a large class of hierarchies of zero-curvature equations
that includes Toda and KdV type hierarchies are investigated. All these
hierarchies are constructed from affine (twisted or untwisted) Kac-Moody
algebras~. Their common feature is that they have some special ``vacuum
solutions'' corresponding to Lax operators lying in some abelian (up to the
central term) subalgebra of~; in some interesting cases such subalgebras
are of the Heisenberg type. Using the dressing transformation method, the
solutions in the orbit of those vacuum solutions are constructed in a uniform
way. Then, the generalized tau-functions for those hierarchies are defined as
an alternative set of variables corresponding to certain matrix elements
evaluated in the integrable highest-weight representations of~. Such
definition of tau-functions applies for any level of the representation, and it
is independent of its realization (vertex operator or not). The particular
important cases of generalized mKdV and KdV hierarchies as well as the abelian
and non abelian affine Toda theories are discussed in detail.Comment: 27 pages, plain Te
Comparing the performance of the SF-6D and the EQ-5D in different patient groups
Introduction: This research aims to explore the performance of the SF-6D and the EQ-5D in patients suffering from asthma, chronic obstructive pulmonary disease, cataracts, and rheumatoid arthritis. In particular, the aim of this research is twofold: 1) to study the level of agreement between the indexes and the descriptive systems of the dimensions of the SF-6D and the EQ-5D, and 2) to analyze the discriminative ability of the instruments. Material and Methods: A sample of 643 patients completed both the SF-36v2 and the EQ-5D. The discriminative ability of the instruments was analyzed. Furthermore, the level of agreement between the indexes and the descriptive systems of the dimensions of the SF-6D and the EQ-5D were studied. The level of agreement between instruments was investigated using correlation coefficients and the Bland-Altman plots, while the influence of medical condition and other socio-demographic variables was analyzed using non-parametric tests. Paired-samples tests were used to identify differences between the scores. Results and Discussion: The results show a strong correlation and agreement between both indexes. Overall, questionnaire indexes differ by medical condition and socio-demographic groups and both instruments are able to discriminate between socio-demographic groups. Conclusion: This study confirmed the hypothesis that the SF-6D generates higher utility values in less healthy individuals. The SF-6D and the EQ-5D seem to perform differently in each of the diseases studied since the descriptive statistics differ between instruments and the level of correlation is not uniform. Results show that the instruments generate different utility values, but there is a strong agreement between both indexes. Thus, the two instruments are not interchangeable and their results cannot be directly comparable.Portuguese Foundation for Science and Technology (Fundacao para a Ciencia e a Tecnologia)info:eu-repo/semantics/publishedVersio
New textures for the lepton mass matrices
We study predictive textures for the lepton mass matrices in which the
charged-lepton mass matrix has either four or five zero matrix elements while
the neutrino Majorana mass matrix has, respectively, either four or three zero
matrix elements. We find that all the viable textures of these two kinds share
many predictions: the neutrino mass spectrum is inverted, the sum of the
light-neutrino masses is close to 0.1 eV, the Dirac phase in the
lepton mixing matrix is close to either or , and the mass term
responsible for neutrinoless double-beta decay lies in between 12 and 22 meV.Comment: 31 pages, 6 figure
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