53 research outputs found

    High energy protons from PKS 1333-33

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    In this letter we give an account of the possible acceleration of protons in the outer radio lobes of the active galaxy PKS 1333-33. We also make estimates of the arrival energy spectrum.Comment: 3 pages revtex, two figures, to appear in Mod. Phys. Lett.

    Brane Worlds, String Cosmology, and AdS/CFT

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    Using the thin-shell formalism we discuss the motion of domain walls in de Sitter and anti-de Sitter (AdS) time-dependent bulks. This motion results in a dynamics for the brane scale factor. We show that in the case of a clean brane the scale factor describes both singular and non-singular universes, with phases of contraction and expansion. These phases can be understood as quotients of AdS spacetime by a discrete symmetry group. We discuss this effect in some detail, and suggest how the AdS/CFT correspondence could be applied to obtain a non perturbative description of brane-world string cosmology

    Variable rest masses in 5-dimensional gravitation confronted with experimental data

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    Cosmological solutions of Einstein equation for a \mbox{5-dimensional} space-time, in the case of a dust-filled universe, are presented. With these solutions we are able to test a hypothetical relation between the rest mass of a particle and the 5th5^{\rm th} dimension. Comparison with experiment strongly refutes the implied dependence of the rest mass on the cosmological time.Comment: Some references adde

    Beyond Analog Gravity: The Case of Exceptional Dynamics

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    We show that it is possible to go beyond the simple kinematical aspects of the analog models of gravity. We exhibit the form of the Lagrangian that describes the dynamics of a self-interacting field ϕ \phi as an interaction between ϕ \phi and its associated effective metric g^μν. \hat{g}^{\mu\nu}. In other words the non-linear equation of motion of the field may be interpreted as the gravitational influence on ϕ \phi by its own effective metric which, in our scheme becomes an active partner of the dynamics of ϕ. \phi. Comment: This new version is an extended version of the previous one. All previous results are mantaine

    Cosmological Effects of Nonlinear Electrodynamics

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    It will be shown that a given realization of nonlinear electrodynamics, used as source of Einstein's equations, generates a cosmological model with interesting features, namely a phase of current cosmic acceleration, and the absence of an initial singularity, thus pointing to a way to solve two important problems in cosmology
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