Could the next generation of cosmology experiments exclude supergravity?

Gravitinos are expected to be produced in any local supersymmetric model. Using their abundance prediction as a function of the reheating energy scale, it is argued that the next generation of Cosmic Microwave Background experiments could exclude supergravity or strongly favor "thermal-like" inflation models if B mode polarized radiation were detected. Galactic cosmic--ray production by evaporating primordial black holes is also investigated as a way of constraining the Hubble mass at the end of inflation. Subsequent limits on the gravitino mass and on the related grand unification parameters are derived.Comment: 8 pages, 5 figures, published version with minor changes, results unchange

CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science

CMB polarization provides a unique window into cosmological inflation; the amplitude of the B-mode polarization from last scattering is uniquely sensitive to the energetics of inflation. However, numerous systematic effects arising from optical imperfections can contaminate the observed B-mode power spectrum. In particular, systematic effects due to the coupling of the underlying temperature and polarization fields with elliptical or otherwise asymmetric beams yield spurious systematic signals. This paper presents a non-perturbative analytic calculation of some of these signals. We show that results previously derived in real space can be generalized, formally, by including infinitely many higher-order corrections to the leading order effects. These corrections can be summed and represented as analytic functions when a fully Fourier-space approach is adopted from the outset. The formalism and results presented in this paper were created to determine the susceptibility of CMB polarization probes of the primary gravitational wave signal but can be easily extended to the analysis of gravitational lensing of the CMB.Comment: 14 pages, 11 figures, 6 tables. Minor corrections included to match published versio

CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science

CMB polarization provides a unique window into cosmological inflation; the amplitude of the B-mode polarization from last scattering is uniquely sensitive to the energetics of inflation. However, numerous systematic effects arising from optical imperfections can contaminate the observed B-mode power spectrum. In particular, systematic effects due to the coupling of the underlying temperature and polarization fields with elliptical or otherwise asymmetric beams yield spurious systematic signals. This paper presents a non-perturbative analytic calculation of some of these signals. We show that results previously derived in real space can be generalized, formally, by including infinitely many higher-order corrections to the leading order effects. These corrections can be summed and represented as analytic functions when a fully Fourier-space approach is adopted from the outset. The formalism and results presented in this paper were created to determine the susceptibility of CMB polarization probes of the primary gravitational wave signal but can be easily extended to the analysis of gravitational lensing of the CMB.Comment: 14 pages, 11 figures, 6 tables. Minor corrections included to match published versio

POKER: Estimating the power spectrum of diffuse emission with complex masks and at high angular resolution

We describe the implementation of an angular power spectrum estimator in the flat sky approximation. POKER (P. Of k EstimatoR) is based on the MASTER algorithm developped by Hivon and collaborators in the context of CMB anisotropy. It works entirely in discrete space and can be applied to arbitrary high angular resolution maps. It is therefore particularly suitable for current and future infrared to sub-mm observations of diffuse emission, whether Galactic or cosmological.Comment: Astronomy and Astrophysics, in pres

Low frequency interference between short synchrotron radiation sources

A recently developed analytical formalism describing low frequency far-field synchrotron radiation (SR) is applied to the calculation of spectral angular radiation densities from interfering short sources (edge, short magnet). This is illustrated by analytical calculation of synchrotron radiation from various assemblies of short dipoles, including an “isolated” highest density infrared SR source

Novel Mg-rich materials for hydrogen storage: bulk and nanoconfined Mg6Pd1 xTMx (TM = Ni, Ag, Cu) compounds and MgH2-TiH2 nanocomposites

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 29-11-2013Tesis cotutelada, leída para obtener el grado de doctor tanto de la Université Paris-Est como de la Universidad Autónoma de MadridNovel Mg-rich materials for hydrogen storage: bulk and nanoconfined Mg6Pd1-xTMx (TM = Ni, Ag, Cu) compounds and MgH2-TiH2 nanocomposites This thesis is dedicated to the study of novel magnesium-rich compounds for solid state hydrogen storage. The aim is to destabilize Mg hydride and accelerate its sorption kinetics by alloying and nanostructuration. Three different kinds of materials have been studied. The first family of materials concerns the Mg6Pd1-xTMx (TM = Ni, Ag, Cu) pseudobinary compounds. Their structural properties and the effects of Pd substitution have been studied by X-ray diffraction, scanning electron microscopy and electron microprobe analyses. Their thermodynamics and kinetics of hydrogenation have been determined by solid-gas reaction. Different hydrogenation mechanisms take place depending on the substituting element. The stability of the metal-hydrogen system is altered by the nature of the phases formed during hydrogenation reaction. Thus, metal to hydride transformation is characterized by at least two absorption plateau pressures. The pressure of the first plateau is similar to that of Mg/MgH2 while the second one occurs at higher pressure. The enthalpy and entropy of reaction are determined to quantify the destabilizing effect of Pd by TM substitution. Best desorption kinetics are found for the Ni containing alloy thanks to the catalytic effect of the Mg2NiH4 phase formed on hydrogenation. The second approach aims to combine alloying with nanostructuration effects. Nanoparticles of Mg6Pd as small as 3 nm are confined into nanoporous carbon matrix. By comparing their hydrogenation properties with those of the bulk alloy, we demonstrate that not only the (de)hydrogenation kinetics are much faster for the nanoparticles, but also that their hydrided state is destabilized. Finally, MgH2-TiH2 nanocomposites were synthesized by mechanical milling under reactive atmosphere. The addition of a catalyst (TiH2) and Mg nanostructuration allow strongly accelerating the sorption kinetics of hydrogen in Mg. To understand the role of the TiH2 phase on the outstanding kinetics of these nanocomposites, their structural properties have been determined by X-ray and neutron diffraction. The existence of a coupled interface between Mg and TiH2 phases is of major importance to facilitate Hmobility within the nanocomposite. Furthermore, it is shown that the TiH2 inclusions inhibit the Mg/MgH2 grain growth, thus maintaining the composites nanostructure during their cycling.Nouveaux matériaux riches en Mg pour le stockage d’hydrogène : composés Mg6Pd1-xMTx (MT = Ni, Ag, Cu) massifs et nanoconfinés et nanocomposites MgH2-TiH2 Cette thèse est consacrée à l’étude de composés riches en magnésium innovants destinés au stockage solide de l’hydrogène. Le but est de déstabiliser l’hydrure de Mg et d’accélérer sa cinétique de sorption par des effets d’alliage et de nano-structuration. Trois différents types de matériaux ont été étudiés. La première famille de matériaux concerne les composés pseudo-binaires Mg6Pd1-xMTx (MT = Ni, Ag, Cu). Leurs propriétés structurales et les effets de substitution du Pd ont été étudiés par diffraction des rayons X, microscopie électronique à balayage et microsonde de Castaing. Les propriétés thermodynamiques et cinétiques d’hydrogénation de ces matériaux ont ensuite été déterminées par réaction solide-gaz. Différents mécanismes d’hydrogénation sont mis en jeu en fonction de l’élément de substitution. La nature des phases formées lors de la réaction d’hydrogénation modifie la stabilité des systèmes métal-hydrogène. Ainsi, la transformation de métal à hydrure est caractérisée par au moins deux plateaux de pression. Le premier plateau a lieu à une pression proche de celle de Mg/MgH2, alors que le second se produit à pression plus élevée. La détermination des valeurs d’enthalpie et d’entropie de réaction ont permis de quantifier la déstabilisation atteinte. Les meilleures cinétiques de désorption sont obtenues pour l’alliage au Ni, grâce à l’effet catalytique de la phase Mg2NiH4 formée lors de l’hydrogénation. La seconde approche vise à combiner les effets d’alliage et de nano-structuration. Des nanoparticules de Mg6Pd atteignant des tailles aussi petites que 3 nm sont confinées dans des matrices carbonées nano-poreuses. En comparant leurs propriétés d'hydrogénation à celles de l’alliage massif équivalent, on démontre non seulement que la cinétique de (dés)hydrogénation des nanoparticules est bien plus rapide, mais aussi que leur état hydrogéné est déstabilisé. Enfin, des nano-composites MgH2-TiH2 ont été synthétisés par broyage mécanique sous atmosphère réactive. L’ajout d’un catalyseur (TiH2) et la nano-structuration du Mg permettent de considérablement accélérer les cinétiques d’absorption et désorption d’hydrogène dans le Mg. Afin de comprendre le rôle de la phase TiH2 sur les propriétés cinétiques remarquables de ces nano-composites, leurs propriétés structurales ont été déterminées par diffraction des rayons X et des neutrons. L’existence d’un couplage à l’interface entre les phases Mg et TiH2 est d’importance majeure pour faciliter la mobilité de H au sein du nano-composite. De plus, il est démontré que les inclusions de TiH2 freinent la croissance de grain de Mg/MgH2, permettant ainsi de maintenir la nanostructuration des composés lors de leur cyclage.Nuevos materiales ricos en Mg para el almacenamiento de hidrógeno: compuestos en volumen y nano-confinados Mg6Pd1-xMTx (MT = Ni, Ag, Cu) y nano-compuestos MgH2-TiH2 Esta tesis está dedicada al estudio de nuevos compuestos ricos en magnesio para el almacenamiento sólido de hidrógeno. El objetivo es desestabilizar el hidruro de Mg y acelerar su cinética de sorción mediante efectos de aleación y nano-estructuración. Tres distintos tipos de materiales se han estudiado. La primera familia de materiales concierne los compuestos pseudo-binarios Mg6Pd1- xMTx (MT = Ni, Ag, Cu). Sus propiedades estructurales y los efectos de sustitución del Pd se han estudiado por difracción de rayos X, microscopía electrónica de barrido y microsonda electrónica. Las propiedades termodinámicas y cinéticas de hidrogenación de estos materiales se determinaron por reacción sólido-gas. Diferentes mecanismos de hidrogenación entran en juego dependiendo del elemento de sustitución. La naturaleza de las fases formadas durante la reacción de hidrogenación modifica la estabilidad de los sistemas metal-hidrógeno. A este respecto, la transformación de metal a hidruro se caracteriza por al menos dos plateaus de presión. El primer plateau ocurre a una presión cercana a la del Mg/MgH2, mientras que el segundo se produce a mayor presión. La determinación de los valores de entalpía y entropía de reacción ha permitido cuantificar la desestabilización alcanzada. Las mejores cinéticas de desorción se obtienen para la aleación con Ni, gracias al efecto catalítico de la fase Mg2NiH4 formada durante la hidrogenación. El segundo enfoque consiste en combinar los efectos de aleación y de nanoestructuración. Nano-partículas de Mg6Pd con tamaños tan pequeños como 3 nm se han confinado en una matriz de carbono nano-poroso. Sus propiedades de hidrogenación se han comparado con las de la aleación en volumen equivalente, demostrando que no sólo la cinética de (de)hidrogenación de las nano-partículas es mucho más rápida, sino también que su estado hidrogenado se ha desestabilizado. Por último, se han sintetizado nano-compuestos MgH2-TiH2 mediante molienda mecánica en atmósfera reactiva. La adición de un catalizador (TiH2) y la nanoestructuración del Mg han permitido acelerar significativamente la cinética de absorción y desorción de hidrógeno por el Mg. Para entender el papel que juega la fase TiH2 en las excelentes propiedades cinéticas de estos nano-compuestos, se han determinado sus propiedades estructurales mediante difracción de rayos X y de neutrones. La existencia de un acoplamiento a la interfase entre el Mg y el TiH2 es clave para facilitar la movilidad de H en el nano-compuesto. Además, se demuestra que las inclusiones de TiH2 ralentizan el crecimiento de grano de Mg/MgH2, manteniendo la nano-estructura de los compuestos durante su ciclado