Ellipsoidal universe in the brane world

We study a scenario of the ellipsoidal universe in the brane world cosmology with a cosmological constant in the bulk . From the five-dimensional Einstein equations we derive the evolution equations for the eccentricity and the scale factor of the universe, which are coupled to each other. It is found that if the anisotropy of our universe is originated from a uniform magnetic field inside the brane, the eccentricity decays faster in the bulk in comparison with a four-dimensional ellipsoidal universe. We also investigate the ellipsoidal universe in the brane-induced gravity and find the evolution equation for the eccentricity which has a contribution determined by the four- and five-dimensional Newton's constants. The role of the eccentricity is discussed in explaining the quadrupole problem of the cosmic microwave background.Comment: 15 pages, 1 figure, Version 3, references added, contents expande

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.