46 research outputs found
Regularization of Brane Induced Gravity
We study the regularization of theories of ``brane induced'' gravity in
codimension . The brane can be interpreted as a thin dielectric with a
large dielectric constant, embedded in a higher dimensional space. The kinetic
term for the higher dimensional graviton is enhanced over the brane. A four
dimensional gravitation is found on the brane at distances smaller than a
critical distance , and is due to the exchange of a massive resonant
graviton. The crossover scale is determined by the mass of the resonance.
The suppression of the couplings of light Kaluza-Klein modes to brane matter
results in a higher dimensional force law at large distances. We show that the
resulting theory is free of ghosts or tachyons.Comment: One reference added. To appear in PRD. 20 pages, 3 figure
On Brane World Cosmological Perturbations
We discuss the scalar cosmological perturbations in a 3-brane world with a 5D
bulk. We first show explicitly how the effective perturbed Einstein's equations
on the brane (involving the Weyl fluid) are encoded into Mukohyama's master
equation. We give the relation between Mukohyama's master variable and the
perturbations of the Weyl fluid, we also discuss the relation between the
former and the perturbations of matter and induced metric on the brane. We show
that one can obtain a boundary condition on the brane for the master equation
solely expressible in term of the master variable, in the case of a perfect
fluid with adiabatic perturbations on a Randall-Sundrum (RS) or
Dvali-Gabadadze-Porrati (DGP) brane. This provides an easy way to solve
numerically for the evolution of the perturbations as well as should shed light
on the various approximations done in the literature to deal with the Weyl
degrees of freedom.Comment: 36 pages, 1 figur
An infinite family of magnetized Morgan-Morgan relativistic thin disks
Applying the Horsk\'y-Mitskievitch conjecture to the empty space solutions of
Morgan and Morgan due to the gravitational field of a finite disk, we have
obtained the corresponding solutions of the Einstein-Maxwell equations. The
resulting expressions are simply written in terms of oblate spheroidal
coordinates and the solutions represent fields due to magnetized static thin
disk of finite extension. Now, although the solutions are not asymptotically
flat, the masses of the disks are finite and the energy-momentum tensor agrees
with the energy conditions. Furthermore, the magnetic field and the circular
velocity show an acceptable physical behavior.Comment: Submitted to IJTP. This paper is a revised and extended version of a
paper that was presented at arXiv:1006.203
Cosmological Spacetimes from Negative Tension Brane Backgrounds
We identify a time-dependent class of metrics with potential applications to
cosmology, which emerge from negative-tension branes. The cosmology is based on
a general class of solutions to Einstein-dilaton-Maxwell theory, presented in
{hep-th/0106120}. We argue that solutions with hyperbolic or planar symmetry
describe the gravitational interactions of a pair of negative-tension
-branes. These spacetimes are static near each brane, but become
time-dependent and expanding at late epoch -- in some cases asymptotically
approaching flat space. We interpret this expansion as being the spacetime's
response to the branes' presence. The time-dependent regions provide explicit
examples of cosmological spacetimes with past horizons and no past naked
singularities. The past horizons can be interpreted as S-branes. We prove that
the singularities in the static regions are repulsive to time-like geodesics,
extract a cosmological `bounce' interpretation, compute the explicit charge and
tension of the branes, analyse the classical stability of the solution (in
particular of the horizons) and study particle production, deriving a general
expression for Hawking's temperature as well as the associated entropy.Comment: 43 pages, 8 figures. Published versio
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Application of free-air CO sub 2 enrichment (FACE) technology to a forest canopy: A simulation study
Forest ecosystems constitute an important part of the planet's land cover. Understanding their exchanges of carbon with the atmosphere is crucial in projecting future net atmospheric CO{sub 2} increases. It is also important that experimental studies of these processes be performed under conditions which are as realistic as possible, particularly with respect to photosynthesis and evapotranspiration. New technology and experimental protocols now exist which can facilitate studying an undisturbed forest canopy under long-term enriched CO{sub 2} conditions. The International Geosphere Biosphere Program of the International Council of Scientific Unions has established a subprogram on Global Change and Terrestrial Ecosystems (GCTE). This program is driven by two major concerns: to be able to predict the effects of global change on the structure and function of ecosystems, and to predict how these changes will control both atmospheric CO{sub 2} and climate, through various feedback pathways. Brookhaven National Laboratory (BNL) has developed a system for exposing field-grown plants to controlled elevated concentrations of atmospheric gases, without use of confining chambers that alter important atmospheric exchange processes. This system, called FACE for Free Air CO{sub 2} Enrichment. This paper focuses on the fluid mechanics of free-air fumigation and uses a numerical simulation model based on superposed gaussian plumes to project how the present ground-based system could be used to fumigate an elevated forest canopy