Stars and (Furry) Black Holes in Lorentz Breaking Massive Gravity

We study the exact spherically symmetric solutions in a class of Lorentz-breaking massive gravity theories, using the effective-theory approach where the graviton mass is generated by the interaction with a suitable set of Stuckelberg fields. We find explicitly the exact black hole solutions which generalizes the familiar Schwarzschild one, which shows a non-analytic hair in the form of a power-like term r^\gamma. For realistic self-gravitating bodies, we find interesting features, linked to the effective violation of the Gauss law: i) the total gravitational mass appearing in the standard 1/r term gets a multiplicative renormalization proportional to the area of the body itself; ii) the magnitude of the power-like hairy correction is also linked to size of the body. The novel features can be ascribed to presence of the goldstones fluid turned on by matter inside the body; its equation of state approaching that of dark energy near the center. The goldstones fluid also changes the matter equilibrium pressure, leading to an upper limit for the graviton mass, m <~ 10^-28 - 10^29 eV, derived from the largest stable gravitational bound states in the Universe.Comment: 22 pages, 4 Figures. Final version to be published in PRD. Typos corrected, comments adde

Gauss-Bonnet gravity renders negative tension braneworlds unstable

We show that the Gauss-Bonnet correction to Einstein gravity induces a gravitational tachyon mode, namely an unstable spin 2 fluctuation, in the Randall-Sundrum I model. We demonstrate that this instability is generically related to the presence of a negative tension brane in the set-up, with or without $Z_2$-symmetry across it. Indeed it is shown that the tachyon mode is a bound state localised on any negative tension brane of co-dimension one, embedded in anti-de Sitter background. We discuss the possible resolution of this instability by the inclusion of induced gravity terms on the branes or by an effective four-dimensional cosmological constant.Comment: published versio

On Brane Inflation Potentials and Black Hole Attractors

We propose a new potential in brane inflation theory, which is given by the arctangent of the square of the scalar field. Then we perform an explicit computation for inflationary quantities. This potential has many nice features. In the small field approximation, it reproduces the chaotic and MSSM potentials. It allows one, in the large field approximation, to implement the attractor mechanism for bulk black holes where the geometry on the brane is de Sitter. In particular, we show, up to some assumptions, that the Friedman equation can be reinterpreted as a Schwarzschild black hole attractor equation for its mass parameter.Comment: 12 pages. Reference updated and minor changes added. Version to appear in Int. J. Mod. Phys.

Electronic Properties and Magnetic Moment Distribution on Perovskite Type Slabs: Sr2FeMoO6, SrFeO3 and SrMoO3

AbstractPerovskite type slabs were excised from the Sr2FeMoO6, SrFeO3 and SrMoO3 bulk double perovskites, respectively, leaving (001) free surfaces. Supercells were built up for each slab, keeping a 10Å initial free space, to optimize the geometry. Once the minimum energy state was identified, the electronic and magnetic properties of the [001] oriented slabs have been calculated within the Density Functional Theory (DFT) scheme, with the Hubbard-corrected Local Density Approximation (LDA+U) and the CA−PZ functional. Magnetic moment for each atom in the systems was calculated; spin values for the Mo atoms are –0.02ħ, − 0.13ħ and 0.56ħ for the SrMoO3 slab system case and they are aligned antiferromagnetically. Contrarily, Mo magnetic moments in the Sr2FeMoO3 slab system align antiferromagnetically to the corresponding Fe atoms, being around 10% in magnitude; meanwhile, Fe moments increase and align ferromagnetically in SrFeO3. The Densities of States (DOS) and band structures were calculated also to study the electronic behaviors. The vacuum region changes from the initial 10Å, as geometry stabilizes for all the slab cases; however, slab images separation evolves notoriously different for each model

Quasilocalized gravity without asymptotic flatness

We present a toy model of a generic five-dimensional warped geometry in which the 4D graviton is not fully localized on the brane. Studying the tensor sector of metric perturbation around this background, we find that its contribution to the effective gravitational potential is of 4D type (1/r) at the intermediate scales and that at the large scales it becomes 1/r^{1+alpha}, 0<alpha=< 1 being a function of the parameters of the model (alpha=1 corresponds to the asymptotically flat geometry). Large-distance behavior of the potential is therefore not necessarily five-dimensional. Our analysis applies also to the case of quasilocalized massless particles other than graviton.Comment: 9 pages, 1 figure; to be published in Phys. Rev.

Braneworld inflation

We discuss various realizations of the four dimensional braneworld inflation in warped geometries of string theory. In all models the inflaton field is represented by a Dp probe brane scalar specifying its position in the warped throat of the compactification manifold. We study existing inflationary throat local geometries, and construct a new example. The inflationary brane is either a D3- or a D5-brane of type IIB string theory. In the latter case the inflationary brane is wrapping a two-cycle of the compactification manifold. We discuss some phenomenological aspects of the model where slow-roll conditions are under computational control.Comment: 31 pages + 6 figures, v2: published PRD versio

Cosmological Rescaling through Warped Space

We discuss a scenario where at least part of the homogeneity on a brane world can be directly related to the hierarchy problem through warped space. We study the dynamics of an anti-D3-brane moving toward the infrared cut-off of a warped background. After a region described by the DBI action, the self-energy of the anti-D3-brane will dominate over the background. Then the world-volume scale of the anti-D3-brane is no longer comoving with the background geometry. After it settles down in the infrared end, the world-volume inhomogeneity will appear, to a Poincare observer, to be stretched by an exponentially large ratio. This ratio is close to that of the hierarchy problem between the gravitational and electroweak scales.Comment: 12 pages, 2 figures; v2, PRD version, comments and references adde

Présence du virus de peste équine type 9 en République algérienne. Identification des souches de virus isolées en 1965-1966

Isolement et identification, en 1965-66, de 14 souches de virus de peste équine type 9, au cours de l'épizootie apparue pour la première fois chez les équidés en Algérie à l'automne 1965 dans le sud algérien et qui s'est étendue en 1966 à plusieurs autres régions de la République Algérienn