Local conservation law and dark radiation in cosmological braneworld

Abstract

In the context of the Randall-Sundrum (RS) single-brane scenario, we discuss the bulk geometry and dynamics of a cosmological brane in terms of the local energy conservation law which exists for the bulk that allows slicing with a maximally symmetric 3-space. This conservation law enables us to define a local mass in the bulk. We show that there is a unique generalization of the dark radiation on the brane, which is given by the local mass. We find there also exists a conserved current associated with the Weyl tensor, and the corresponding local charge, which we call the Weyl charge, is given by the sum of the local mass and a certain linear combination of the components of the bulk energy-momentum tensor. This expression of the Weyl charge relates the local mass with the projected Weyl tensor, Eµν, which plays a central role in the geometrical formalism of the RS braneworld. On the brane, in particular, this gives a decomposition of the projected Weyl tensor into the local mass and the bulk energy-momentum tensor. Then, as an application of these results, we consider a null dust model for the bulk energy-momentum tensor and discuss the black hole formation in the bulk. We investigate the causal structure by identifying the locus of the apparent horizon and clarify possible brane trajectories in the bulk. We find that the brane stays always outside the black hole as long as it is expanding. We also find an upper bound on the value of the Hubble parameter in terms of the matter energy density on the brane, irrespective of the energy flux emitted from the brane.

Dynamics of radiating braneworlds

“…See [8] for further discussion. The above equations lead to the modified Friedmann equation (1), and an equation governing the evolution of C [2] (valid outside the apparent horizon)…”

Generalized Misner-Sharp energy inf(R)gravity

“…For a spherically symmetric spacetime, one can define the Kodama vector as [25,26] 9) where ǫ µν = ǫ ab (dx a ) µ (dx b ) ν , and ǫ ab is the volume element of (M 2 , h ab ). For the spherically symmetric spacetime (3.1), we have…”

Hawking Radiation of Apparent Horizon in a FRW Universe as Tunneling Beyond Semiclassical Approximation

“…In a dynamical setting, there is a preferred time direction given by the Kodama vector [53][54][55][56], which is a natural analogue to the Killing vector to define the energy of a particle. Related to this choice of time direction, we can give the form of action solutions in the dynamical case.…”