Cosmology on a cosmic ring

Abstract

Abstract.We derive the modified Friedmann equations for a generalization of the Dvali-GabadadzePorrati (DGP) model in which the brane has one additional compact dimension. The main new feature is the emission of gravitational waves into the bulk. We study two classes of solutions: First, if the compact dimension is stabilized, the waves vanish and one exactly recovers DGP cosmology. However, a stabilization by means of physical matter is not possible for a tension-dominated brane, thus implying a late time modification of 4D cosmology different from DGP. Second, for a freely expanding compact direction, we find exact attractor solutions with zero 4D Hubble parameter despite the presence of a 4D cosmological constant. The model hence constitutes an explicit example of dynamical degravitation at the full nonlinear level. Without stabilization, however, there is no 4D regime and the model is ruled out observationally, as we demonstrate explicitly by comparing to supernova data.

Brane induced gravity: Ghosts and naturalness

“…The jumps in the r-derivative of all the remaining constrained gaugeinvariant quantities (W i , P and Q) can readily be obtained from the r-derivatives of the corresponding bulk equations. As a consistency check, we explicitly verified that all the junction conditions, together with the bulk equations, imply the energy conservation equations (28), as is guaranteed by the Gauss-Codazzi equations.…”

“…As a consistency check, we explicitly verified that all the junction conditions, together with the bulk equations, imply the energy conservation equations (28), as is guaranteed by the Gauss-Codazzi equations.…”

“…The origin as a codimension-two model requires the existence of a regular axis in the interior region, which will be demanded throughout this work. Otherwise, the same action could also describe a topologically distinct model without an axis[28].…”

Rotating kinky braneworlds

“…The scalar winds around the brane, thereby providing the angular pressure needed to stabilize the cylinder's radial direction. Building up on these result, later work often used an angular pressure component of the brane energy-momentum tensor to effectively implement this stabilisation mechanism, rather than resolving it in terms of a worldvolume scalar field (see for example [11,21,33]). This work is guided by the question as to whether it is possible to consistently embed the hollow cylinder construction in a (classical) mircrophysical theory that resolves the brane at high energies.…”