Massive Gravity in de Sitter Space via Gravitational Higgs Mechanism

In this paper we discuss massive gravity in de Sitter space via gravitational Higgs mechanism, which provides a nonlinear definition thereof. The Higgs scalars are described by a nonlinear sigma model, which includes higher derivative terms required to obtain the Fierz-Pauli mass term. Using the aforesaid non-perturbative definition, we address appearance of an enhanced local symmetry and a null norm state in the linearized massive gravity in de Sitter space at the special value of the graviton mass to the Hubble parameter ratio. By studying full non-perturbative equations of motion, we argue that there is no enhanced symmetry in the full nonlinear theory. We then argue that in the full nonlinear theory no null norm state is expected to arise at the aforesaid special value. This suggests that no ghost might be present for lower graviton mass values and the full nonlinear theory might be unitary for all values of the graviton mass and the Hubble parameter with no van Dam-Veltman-Zakharov discontinuity. We argue that this is indeed the case by studying full nonlinear Hamiltonian for the relevant conformal and helicity-0 longitudinal modes. In particular, we argue that no negative norm state is present in the full nonlinear theory.Comment: 22 pages, comments and references added. Phys.Rev.D versio

A cluster model with random anisotropy for hysteresis jumps in CeNi1−x_{1-x}Cux_{x} alloys

Some Cerium compounds exhibit hysteresis cycles with sharp macroscopic jumps in the magnetization at very low temperatures. This effect is attributed to the formation of clusters in which the anisotropy competes with the applied magnetic field. Here, we present a simple model where a lattice of ferromagnetically coupled spins is separated in clusters of random sizes and with random anisotropy. Within this model, we obtain hysteresis cycles presenting jumps that behave in a similar way that the experimental ones, and that disappear when increasing the temperature. The results are in good agreement with the hysteresis cycles measured at very low temperatures in CeNi$_{1-x}$Cu$_{x}$ and the comparison with these experimental results allows to discriminate the relative importance of the mechanisms driving the thermal evolution of the cycles.Comment: Accepted in PR

Schwarzschild solution in brane induced gravity

The metric of a Schwarzschild solution in brane induced gravity in five dimensions is studied. We find a nonperturbative solution for which an exact expression on the brane is obtained. We also find a linearized solution in the bulk and argue that a nonsingular exact solution in the entire space should exist. The exact solution on the brane is highly nontrivial as it interpolates between different distance scales. This part of the metric is enough to deduce an important property -- the ADM mass of the solution is suppressed compared to the bare mass of a static source. This screening of the mass is due to nonlinear interactions which give rise to a nonzero curvature outside the source. The curvature extends away from the source to a certain macroscopic distance that coincides with the would-be strong interaction scale. The very same curvature shields the source from strong coupling effects. The four dimensional law of gravity, including the correct tensorial structure, is recovered at observable distances. We find that the solution has no vDVZ discontinuity and show that the gravitational field on the brane is always weak, in spite of the fact that the solution is nonperturbative.Comment: 23 pages, 2 figures, repetitions removed, PRD versio

Comparison of experimental and numerical sloshing loads in partially filled tanks

Sloshing phenomenon consists in the movement of liquids inside partially filled tanks, whichgenerates dynamic loads on the tank structure. Resulting impact pressures are of great importance in assessingstructural strength, and their correct evaluation still represents a challenge for the designer due to the highnonlinearities involved, with complex free surface deformations, violent impact phenomena and influence of airtrapping. In the present paper a set of two-dimensional cases for which experimental results are available areconsidered to assess merits and shortcomings of different numerical methods for sloshing evaluation, namely twocommercial RANS solvers (FLOW-3D and LS-DYNA), and two own developed methods (Smoothed ParticleHydrodynamics and RANS). Impact pressures at different critical locations and global moment induced by watermotion for a partially filled tank with rectangular section having a rolling motion have been evaluated and resultsare compared with experiments

Luján (provincia de Buenos Aires, Argentina): imagen y destino turístico. Contribución al análisis de una perspectiva el patrimonio territorial

XII Coloquio de Geografía del Turismo, Ocio y Recreación de la Asociación de Geógrafos Españoles. Colmenarejo (Madrid), del 17 al 19 de junio de 2010

Significado do turismo de peregrinación para o desenvolvemento local. Caso das peregrinacións á Basílica Nacional da Nosa Señora da Pura e Limpa Concepción do Río Luján, provincia de Bos Aires, Arxentina

[Resumen] Entre las características culturales que contribuyeron a forjar el valor turístico de la actual ciudad de Luján de la Provincia de Buenos Aires, Argentina, descuella, en particular, la religiosa, factor que constituye un elemento clave de la concepción de cualquier estrategia de desarrollo local que se asuma. El significado de la virgen de Luján, Nuestra Señora de la Pura y Limpia Concepción del río Luján, su historia, prácticamente, hilvana el relato científicamente edificado acerca del asentamiento y de la sociedad, lujanenses, en una amalgama permanentemente renovada por el fenómeno singular, por la diversidad de sus expresiones, de las peregrinaciones a Virgen y a la Basílica Nacional Nuestra Señora de Luján.[Resumo] Entre as características culturais que contribuíron a forzar o valor turístico da actual cidade de Luján da provincia de Bos Aires, Arxentina, sobresae, en particular, a relixiosa, factor que constitúe un elemento clave da concepción de calquera estratexia de desenvolvemento local que se asuma. O significado da virxe de Luján, A Nosa Señora da Pura e Limpa concepción do río Luján, a súa historia, practicamente ganduxa o relato cientificamente edificado acerca do asentamento e da sociedade lujanenses, nunha amálgama permanentemente renovada polo fenómeno singular, pola diversidade das súas expresións, das peregrinacións á Virxe e á Basílica Nacional da Nosa Señora de Luján.[Abstract] This includes an analysis of the promotion of the Camino de Santiago over the last few decades, the context in which this was carried out, the parties involved in the process, the promotional strategies to attract tourists and travel agencies, sponsorship, and collaboration with the private sector, with the political institutions, with the media and with civil society. It also examines the communication activities carried out, the materials used with their identifying symbols (mascot, logotype, credentials), the changes of image under the Xacobeo brand, and the link between the communication carried out (image projected), the confirmed initial image and the a posteriori image perceived by visitors

Prior-based Coregistration and Cosegmentation

We propose a modular and scalable framework for dense coregistration and cosegmentation with two key characteristics: first, we substitute ground truth data with the semantic map output of a classifier; second, we combine this output with population deformable registration to improve both alignment and segmentation. Our approach deforms all volumes towards consensus, taking into account image similarities and label consistency. Our pipeline can incorporate any classifier and similarity metric. Results on two datasets, containing annotations of challenging brain structures, demonstrate the potential of our method.Comment: The first two authors contributed equall

How (Not) to Palatini

We revisit the problem of defining non-minimal gravity in the first order formalism. Specializing to scalar-tensor theories, which may be disguised as `higher-derivative' models with the gravitational Lagrangians that depend only on the Ricci scalar, we show how to recast these theories as Palatini-like gravities. The correct formulation utilizes the Lagrange multiplier method, which preserves the canonical structure of the theory, and yields the conventional metric scalar-tensor gravity. We explain the discrepancies between the na\"ive Palatini and the Lagrange multiplier approach, showing that the na\"ive Palatini approach really swaps the theory for another. The differences disappear only in the limit of ordinary General Relativity, where an accidental redundancy ensures that the na\"ive Palatini works there. We outline the correct decoupling limits and the strong coupling regimes. As a corollary we find that the so-called `Modified Source Gravity' models suffer from strong coupling problems at very low scales, and hence cannot be a realistic approximation of our universe. We also comment on a method to decouple the extra scalar using the chameleon mechanism.Comment: 18 pages, LaTeX; added references and minor improvements in sec