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# Exactly solvable model for cosmological perturbations in dilatonic brane worlds

Physical review D: Particles and fields 07/2003; DOI: 10.1103/PhysRevD.68.103512

Source: arXiv

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**ABSTRACT:**Motivated by the fact that cosmological perturbations of inflationary quantum origin were born Gaussian, the search for non-Gaussianities in the cosmic microwave background (CMB) anisotropies is considered as the privileged probe of non-linear physics in the early universe. Cosmic strings are active sources of gravitational perturbations and incessantly produce non-Gaussian distortions in the CMB. Even if, on the currently observed angular scales, they can only contribute a small fraction of the CMB angular power spectrum, cosmic strings could actually be the main source of its non-Gaussianities. In this article, after having reviewed the basic cosmological properties of a string network, we present the signatures Nambu-Goto cosmic strings would induce in various observables ranging from the one-point function of the temperature anisotropies to the bispectrum and trispectrum. It is shown that string imprints are significantly different than those expected from the primordial type of non-Gaussianity and could therefore be easily distinguished. Comment: 50 pages, 20 figures, uses iopart. Misprints corrected, references added, matches published versionAdvances in Astronomy 05/2010; -
##### Article: Warped Radion Inflation

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**ABSTRACT:**We show that the radion in a warped geometry bounded by two branes can have a potential suitable for inflation. Our construction is based upon a solution known in string theory as the linear dilaton, in which the back-reaction from a bulk scalar \Phi is exactly accounted for. The radion, stabilized by \Phi, is much heavier than the TeV scale and its couplings to the standard model are much more suppressed than in the usual Randall-Sundrum solution. We present a new formalism for obtaining approximate time-dependent solutions, based on perturbing the exact solution to the coupled Einstein and scalar field equations in the bulk. It allows the radion potential to be computed directly in terms of the brane potentials for \Phi. We show that simple exponential potentials on the branes can lead to a 4D radion potential with a flattened hilltop form, yielding inflation with a spectral index of typically n_s=0.96 and no higher than 0.99. With more complicated brane potentials, the descent from the hilltop can be a linear potential, giving a tensor-to-scalar ratio as large as r=0.07 with n_s=0.974. The couplings of the radion to the standard model particles are dictated by general covariance, so the details of reheating are explicitly calculable, leading to a reheat temperature of at least 10^7 GeV. The quantum corrections to the inflaton potential from its couplings to matter are also calculable and are shown to be small, so that the prediction for the shape of the potential is under theoretical control, even with superPlanckian field excursions.Journal of High Energy Physics 11/2011; 2012(2). · 5.62 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We have considered gravity in a five-dimensional warped product space-time, with a time-dependent warp factor and a time-dependent extra dimension. The field equations have been solved for a spatially flat FRW brane and the energy conditions and the nature of bulk geometry have been examined. At low energies, the trapping of fields within the brane implies a correlation between the warp factor and the extra-dimensional scale factor. Generally, the bulk is not conformally flat. At high energies, the bulk is sourced by a dilaton-like minimally coupled scalar field, which depends on the warp factor. Both the bulk and the brane are found to be Anti de Sitter, with some exceptions.07/2012;

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