Cosmological perturbation spectra from SL(4,R)-invariant effective actions

We investigate four-dimensional cosmological vacuum solutions derived from an effective action invariant under global SL(n,R) transformations. We find the general solutions for linear axion field perturbations about homogeneous dilaton-moduli-vacuum solutions for an SL(4,R)-invariant action and find the spectrum of super-horizon perturbations resulting from vacuum fluctuations in a pre big bang scenario. We show that for SL(n,R)-invariant actions with n>3 there exists a regime of parameter space of non-zero measure where all the axion field spectra have positive spectral tilt, as required if light axion fields are to provide a seed for anisotropies in the microwave background and large-scale structure in the universe.Comment: 8 pages, 3 figures, revtex plus epsf, minor typos corrected, version to appear in Physical Review

Cosmological perturbations in the bulk and on the brane

We study cosmological perturbations in a brane-world scenario where the matter fields live on a four-dimensional brane and gravity propagates in the five-dimensional bulk. We present the equations of motion in an arbitrary gauge for metric perturbations in the bulk and matter perturbations on the brane. Gauge-invariant perturbations are then constructed corresponding to perturbations in longitudinal and Gaussian normal gauges. Longitudinal gauge metric perturbations may be directly derived from three master variables (separately describing scalar, vector and tensor metric perturbations) which obey five-dimensional wave-equations. Gaussian normal gauge perturbations are directly related to the induced metric perturbations on the brane with the additional bulk degrees of freedom interpreted as an effective Weyl energy-momentum tensor on the brane. We construct gauge-invariant perturbations describing the effective density, momentum and pressures of this Weyl fluid at the brane and throughout the bulk. We show that there exist gauge-invariant curvature perturbations on the brane and in the bulk that are conserved on large-scales when three-dimensional spatial gradients are negligible.Comment: 26 pages, 1 figure; equations for 5D longitudinal gauge perturbations in terms of master variables corrected. Published versio

Cosmic vorticity on the brane

We study vector perturbations about four-dimensional brane-world cosmologies embedded in a five-dimensional vacuum bulk. Even in the absence of matter perturbations, vector perturbations in the bulk metric can support vector metric perturbations on the brane. We show that during de Sitter inflation on the brane vector perturbations in the bulk obey the same wave equation for a massless five-dimensional field as found for tensor perturbations. However, we present the second-order effective action for vector perturbations and find no normalisable zero-mode in the absence of matter sources. The spectrum of normalisable states is a continuum of massive modes that remain in the vacuum state during inflation.Comment: 10 pages, latex with revtex. Expanded discussion of observational effects and minor corrections. Version to appear in Phys. Rev.

Prevention in practice – a summary.

Background: This paper is a summary document of the Prevention in Practice Conference and Special Supplement of BMC Oral Health. It represents the consensus view of the presenters and captures the questions, comments and suggestions of the assembled audience. Methods: Using the prepared manuscripts for the conference, collected materials from scribes during the conference and additional resources collated in advance of the meeting, authors agreed on the summary document. Results: The Prevention in Practice conference aimed to collate information about which diseases could be prevented in practice, how diseases could be identified early enough to facilitate prevention, what evidence based therapies and treatments were available and how, given the collective evidence, could these be introduced in general dental practice within different reimbursement models. Conclusions: While examples of best practice were provided from both social care and insurance models it was clear that further work was required on both provider and payer side to ensure that evidence based prevention was both implemented properly but also reimbursed sufficiently. It is clear that savings can be made but these must not be overstated and that the use of effective skill mix would be key to realizing efficiencies. The evidence base for prevention of caries and periodontal disease has been available for many years, as have the tools and techniques to detect, diagnose and stage the diseases appropriately. Dentistry finds itself in a enviable position with respect to its ability to prevent, arrest and reverse much of the burden of disease, however, it is clear that the infrastructure within primary care must be changed, and practitioners and their teams appropriately supported to deliver this paradigm shift from a surgical to a medical model