Gravitating field-theoretical branes and their excitations

This thesis is devoted to studying field-theoretical branes in warped geometries, with emphasis on brane excitations and properties of background solutions. Firstly, we examine the features of a model in which our universe is represented by a local string-like defect embedded in a six-dimensional space-time with warped geometry. We demonstrate that in order to satisfy the dominant energy condition, the metric exterior to the defect's core must depend on its thickness. As a result of this dependence, in the limit of the string's thickness going to zero, either the solution no longer localizes the gravity on the defect, or the ratio of the six-dimensional Planck mass to the four-dimensional one diverges. Next, we propose and study a toy model allowing to investigate the phenomenon of quasilocalization. When applied to gravity, our setup can be seen as a (toy) model of a warped geometry in which the graviton is not fully localized on the brane. Studying the tensor sector of metric perturbations around this background, we find that its contribution to the effective gravitational potential is of four-dimensional type 1/r at intermediate scales and that at large scales it becomes 1/rα, 1 <α ≤ 2 being a function of the parameters of the model (α = 2 corresponds to the asymptotically flat geometry). Large-distance behavior of the potential depends therefore on the asymptotic geometry and does not need to be "five-dimensional" (1/r2). Our analysis applies also to the case of quasilocalized massless particles other than the graviton. Finally, we investigate the fate of the translational zero mode of a domain wall in a fivedimensional space-time in the presence of gravity, studying the scalar perturbations of a thick gravitating domain wall with a well defined non-gravitating limit and AdS asymptotics. Our analysis reveals the existence of a wide resonance, which can be seen as a relic of the translational zero mode present in the domain wall in the absence of gravity. The presence of this resonance ensures the continuity of physical quantities (such as the static potential between sources) in the limit when the Planck mass tends to infinity. Provided that the width of the domain wall is much smaller than the AdS radius of the space-time, the parameters of the resonance do not depend on the details of the domain wall structure, but are entirely determined by the geometry of the space-time.

    Thèse École polytechnique fédérale de Lausanne EPFL, n° 3355 (2005)
    Section de physique
    Faculté des sciences de base
    Institut de théories des phénomènes physiques
    Laboratoire de physique des particules et de cosmologie
    Jury: Ruth Durrer, Jean-Jacques Meister, Tatsuya Nakada, Riccardo Rattazzi

    Public defense: 2005-11-25


    Record created on 2005-09-22, modified on 2016-08-08


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