This thesis is devoted to studying two important aspects of braneworld physics: their cosmology and their holography. We examine the Einstein equations induced on a general (n − 2)-brane of arbitrary tension, embedded in some n-dimensional bulk. The brane energy-momentum tensor enters these equations both linearly and quadratically. From the point of view of a homogeneous and isotropic brane we...

We consider a generalisation of the DGP model, by adding a second brane with localised curvature, and allowing for a bulk cosmological constant and brane tensions. We study radion and graviton fluctuations in detail, enabling us to check for ghosts and tachyons. By tuning our parameters accordingly, we find bigravity models that are free from ghosts and tachyons. These models will lead to large...

We consider a dynamical brane world in a six-dimensional spacetime containing a singularity. Using the Israel conditions we study the motion of a 4-brane embedded in this setup. We analyse the brane behaviour when its position is perturbed about a fixed point and solve the full nonlinear dynamics in the several possible scenarios. We also investigate the possible gravitational shortcuts and cal...

Gravity in five-dimensional braneworld backgrounds often exhibits problematic features, including kinetic ghosts, strong coupling, and the vDVZ discontinuity. These problems are an obstacle to producing and analyzing braneworld models with interesting and potentially observable modifications of 4d gravity. We examine these problems in a general AdS5/AdS4 setup with two branes and localized curv...

The main cosmological models on the brane are presented. A generic equation is given, from which the Friedmann equations of the Randall-Sundrum, induced gravity, Gauss-Bonnet and the combined induced gravity and Gauss-Bonnet cosmological models are obtained. We discuss the modifications they bring to the standard cosmology and the main features of their inflationary dynamics. Talk given at Pasc...

In recent papers on Randall-Sundrum D-braneworld model with Z2 symmetry, it was shown that the effective gravity does not work as usual, that is, the gravity does not couple to the gauge field localised on the brane in a usual way. At first glance there are two possibilities to avoid this serious problem. One is to remove the Z2 symmetry and another is to consider a non-BPS state. In this paper...

I review some aspects of warped braneworld cosmologies which have some hope of leading to alternatives to in ation. Afterwards, recent work on density perturbations in this context is discussed.

We have studied the stability of wormhole geometries, under massless scalar, electromagnetic, and axial gravitational perturbations, in context higher dimensional spacetimes. Intriguingly, construction a spacetime presence dimensions, known as braneworld wormholes, does not require existence exotic matter fields, unlike scenario four dimensions. Being nonvacuum spacetime, effective potential ex...