Brane cosmology, Weyl fluid, and density perturbations

Abstract

We develop a technique to study relativistic perturbations in the generalised brane cosmological scenario, which is a generalisation of the multi-fluid cosmological perturbations to brane cosmology.The novelty of the technique lies in the inclusion of a radiative bulk which is responsible for bulkbrane energy exchange, and in turn, modifies the standard perturbative analysis to a great extent.The analysis involves a geometric fluid -called the Weyl fluid -whose nature and role have been studied extensively both for the empty bulk and the radiative bulk scenario. Subsequently, we find that this Weyl fluid can be a possible geometric candidate for dark matter in this generalised brane cosmological framework.

Galactic rotation curves in brane world models

“…Similar interpretations of the dark matter as bulk effects have been also considered in Pal, Bharadwaj & Kar (2005) and Pal (2008), where it was also shown that it is possible to model the X-ray profiles of clusters of galaxies, without the need for dark matter.…”

Covariant gravitational dynamics in 3+1+1 dimensions

“…First we express H a , E a , F ab and H ab from ( 37), ( 50), ( 43) and ( 49) respectively and we employ definitions ( 14), (15) in order to introduce E ab and H ab in place of E ab and H ab . Inserting these into the system of equations given by the following equations: (41), ( 29), ( 54), (57)-(66), ( 27), (30), (31), (38), (39), (40), (58)-( 61), (60), (71) and (72), evaluated at the brane, we obtain a system of equations to be referred to as the brane equations. These equations are either evolution or constraint equations on the brane and for a generic asymmetric embedding are presented in appendix C. The evolutions refer to the quantities , K a , , ω a , σ ab , E, E a , E ab , H ab .…”

“…At a technical level, the latter is obstructed by the lack of closure of the perturbation equations on the brane. Despite impressive developments [28]- [40], many questions remain unanswered. Although we cannot overcome well-known difficulties, we expect our new formalism will provide the most convenient and complete toolchest for approaching the problems.…”