874 research outputs found
Fermion masses in SUSY SO(10) with type II seesaw: a non-minimal predictive scenario
A predictive framework for fermion masses and mixing is given by the
supersymmetric SO(10) model with one 10, one bar126, one 126 and one 210 Higgs
representations, and type II seesaw dominating the neutrino mass matrix. We
investigate the origin of the tension between this model and lepton mixing data
and refine previous numerical analyses. We discuss an extension of the minimal
model that includes one 120 Higgs chiral superfield representation. This
exhausts the possible renormalizable contributions to the Yukawa sector. In
spite of the increase in the number of parameters the predictivity of the
minimal setting is not spoiled. We argue that the contributions to fermion
masses due to the doublet components of 120 can be naturally small compared to
those of 10 and 126, thus acting as a perturbation in the fermion mass
generation. The antisymmetric nature of the 120 Yukawa coupling affects at
leading order the determination of the mixing angles and it allows to remove
the inconsistencies between predictions and data on the neutrino parameters. An
improvement in the experimental bound on |Ue3| can tell this scenario from the
minimal model.Comment: 11 pages, 3 figures; Note and references added on new KamLAND dat
Large neutrino mixing and normal mass hierarchy: a discrete understanding
We discuss the possibility of flavor symmetries to explain the pattern of
charged lepton and neutrino masses and mixing angles. We emphasize what are the
obstacles for the generation of an almost maximal atmospheric mixing and what
are the minimal ingredients to obtain it. A model based on the discrete
symmetry is constructed, which leads to the dominant -block in
the neutrino mass matrix, thus predicting normal hierarchy. This symmetry makes
it possible to reproduce current data and predicts
and strongly suppressed neutrinoless
-decay. Moreover, it implies a relation between lepton and quark mixing
angles: . The Cabibbo mixing can
also be reproduced and . is
thus a candidate to describe all the basic features of Standard Model fermion
masses and mixing.Comment: 9 pages, revtex, 1 eps figure; clarifications and comments added in
sections III.A.1. and III.C.; typos corrected; several references adde
A note on semi-conjugacy for circle actions
We define a notion of semi-conjugacy between orientation-preserving actions of a group on the circle, which for fixed point free actions coincides with a classical definition of Ghys. We then show that two circle actions are semi-conjugate if and only if they have the same bounded Euler class. This settles some existing confusion present in the literature
Duality in Left-Right Symmetric Seesaw Mechanism
We consider type I+II seesaw mechanism, where the exchanges of both
right-handed neutrinos and isotriplet Higgs bosons contribute to the neutrino
mass. Working in the left-right symmetric framework and assuming the mass
matrix of light neutrinos and the Dirac-type Yukawa couplings to be
known, we find the triplet Yukawa coupling matrix , which carries the
information about the masses and mixing of the right-handed neutrinos. We show
that in this case there exists a duality: for any solution , there is a dual
solution , where is the VEV of the triplet Higgs.
Thus, unlike in pure type I (II) seesaw, there is no unique allowed structure
for the matrix . For lepton generations the number of solutions is
. We develop an exact analytic method of solving the seesaw non-linear
matrix equation for .Comment: 4 pages, revtex, small clarifications added, title changed to match
published versio
The Averaging Method for Asymptotic Evolutions I: Stochastic Differential Equations
Asymptotic evolutions of open systems are studied. Conditions are given under which successive approximate evolutions obtained by the method of averaging are asymptotic to the exact evolution of the open system. It is shown that these conditions are satisfied in the case of stochastic differential equations which describe the evolution of spins in random magnetic fields
Estudio no destructivo del interior de piezas de valor histórico mediante gammagrafías
La tecnología de Tomografía de Hormigón Armado desarrollada por THASA ha sido aplicada al estudio de piezas ornamentales y otras de valor histórico con el objeto de examinar el interior de las mismas e investigar, en algunos casos, la existencia, configuración y condición de refuerzos metálicos y en otro caso, la existencia de huecos producidos por termitas en vigas de madera. En este trabajo se discuten detalles metodológicos y resultados alcanzados en los casos de las estatuas ubicadas en el coronamiento del Palacio de Tribunales en la Ciudad Autónoma de Buenos Aires, en dragones colgantes de las torres de la Basílica de Luján y en las vigas del techo de la Capilla Doméstica, construida en 1660 y declarada patrimonio de la humanidad por la UNESCO, ubicada en la manzana jesuítica en la Ciudad de Córdoba. El carácter pionero de la investigación de oquedades en madera realizada en este último caso hizo necesario la construcción de modelos de simulación que resultan de utilidad para otras aplicaciones similares
Removing Ambiguities in the Neutrino Mass Matrix
We suggest that the weak-basis independent condition det(M_nu)=0 for the
effective neutrino mass matrix can be used in order to remove the ambiguities
in the reconstruction of the neutrino mass matrix from input data available
from present and future feasible experiments. In this framework, we study the
full reconstruction of M_nu with special emphasis on the correlation between
the Majorana CP-violating phase and the various mixing angles. The impact of
the recent KamLAND results on the effective neutrino mass parameter is also
briefly discussed.Comment: 11 pages, 4 figures. Comments and references added; final version to
appear in Phys. Lett.
Peroxisome proliferator-activated receptor α (PPARα) protects against oleate-induced INS-1E beta cell dysfunction by preserving carbohydrate metabolism
Aims/hypothesis: Pancreatic beta cells chronically exposed to fatty acids may lose specific functions and even undergo apoptosis. Generally, lipotoxicity is triggered by saturated fatty acids, whereas unsaturated fatty acids induce lipodysfunction, the latter being characterised by elevated basal insulin release and impaired glucose responses. The peroxisome proliferator-activated receptor α (PPARα) has been proposed to play a protective role in this process, although the cellular mechanisms involved are unclear. Methods: We modulated PPARα production in INS-1E beta cells and investigated key metabolic pathways and genes responsible for metabolism-secretion coupling during a culture period of 3days in the presence of 0.4mmol/l oleate. Results: In INS-1E cells, the secretory dysfunction primarily induced by oleate was aggravated by silencing of PPARα. Conversely, PPARα upregulation preserved glucose-stimulated insulin secretion, essentially by increasing the response at a stimulatory concentration of glucose (15mmol/l), a protection we also observed in human islets. The protective effect was associated with restored glucose oxidation rate and upregulation of the anaplerotic enzyme pyruvate carboxylase. PPARα overproduction increased both β-oxidation and fatty acid storage in the form of neutral triacylglycerol, revealing overall induction of lipid metabolism. These observations were substantiated by expression levels of associated genes. Conclusions/interpretation: PPARα protected INS-1E beta cells from oleate-induced dysfunction, promoting both preservation of glucose metabolic pathways and fatty acid turnove
Radiative corrections to neutrino mass matrix in the Standard Model and beyond
We study the effect of radiative corrections on the structure of neutrino
mass matrix. We analyze the renormalization of the matrix from the electroweak
scale to the scale at which the effective operator that gives
masses to neutrinos is generated. Apart from Standard Model and MSSM,
non-standard extensions of SM are considered at a scale intermediate
between and . We find that the dominant structure of the neutrino
mass matrix does not change. SM and MSSM corrections produce small (few
percents) independent renormalization of each matrix element. Non-standard
(flavor changing) corrections can modify strongly small (sub-dominant) matrix
elements, which are important for the low energy phenomenology. In particular,
we show that all sub-dominant elements can have purely radiative origin, being
zero at . The set of non-zero elements at can be formed by (i)
diagonal elements (unit matrix); (ii) and ; (iii)
and -block elements; (iv) -block elements. In the case of
unit matrix, both atmospheric and solar mixing angles and mass squared
differences are generated radiatively.Comment: 22 pages, 5 eps figures, JHEP3.cls, some clarifications and one
reference adde
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