12,366 research outputs found
Gravity in the Randall-Sundrum Brane World
We discuss the weak gravitational field created by isolated matter sources in
the Randall-Sundrum brane-world. In the case of two branes of opposite tension,
linearized Brans-Dicke (BD) gravity is recovered on either wall, with different
BD parameters. On the wall with positive tension the BD parameter is larger
than 3000 provided that the separation between walls is larger than 4 times the
AdS radius. For the wall of negative tension, the BD parameter is always
negative but greater than -3/2. In either case, shadow matter from the other
wall gravitates upon us. For equal Newtonian mass, light deflection from shadow
matter is 25 % weaker than from ordinary matter. Hence, the effective mass of a
clustered object containing shadow dark matter would be underestimated if
naively measured through its lensing effect. For the case of a single wall of
positive tension, Einstein gravity is recovered on the wall to leading order,
and if the source is stationary the field stays localized near the wall. We
calculate the leading Kaluza-Klein corrections to the linearized gravitational
field of a non-relativistic spherical object and find that the metric is
different from the Schwarzschild solution at large distances. We believe that
our linearized solution corresponds to the field far from the horizon after
gravitational collapse of matter on the brane.Comment: 8 pages, 1 figure. Replaced with revised version to be published in
Phys. Rev. Lett. Some comments adde
Radiating sources in higher-dimensional gravity
We study a time-dependent 5D metric which contains a static 4D sub-metric
whose 3D part is spherically symmetric. An expansion in the metric coefficient
allow us to obtain close-to Schwarzschild approximation to a class of
spherically-symmetric solutions. Using Campbell's embedding theorem and the
induced-matter formalism we obtain two 4D solutions. One describes a source
with the stiff equation of state believed to be applicable to dense
astrophysical objects, and the other describes a spherical source with a radial
heat flow.Comment: Latex, 20 pages, no figures. to appear in J. Math. Phy
Why supersymmetry should be restored at the TeV scale
It is explained why the curvature associated to the vacuum energy density
arising from SUSY breaking cannot be completely transferred to the extra
spatial dimensions of a bulk space-time manifold, and it is shown -- without
using hierarchy arguments but only the results of current large-scale
observations -- why the Tev scale should correspond to the maximal allowed
SUSY-breaking scale.Comment: 6 pages. Essay written for the 2008 Awards for Essays on Gravitation
(Gravity Research Foundation, USA), and awarded with "Honorable Mention
The discovery circumstances of Earth-approaching asteroids
The discovery circumstances are analyzed for all Earth-approaching asteroids detected in the last twenty-four years. In particular, topocentric angular velocities, opposition distance, geocentric and heliocentric distances, phase angle, and lunar phase at discover were calculated in an effort to separate any selection effects between chance and purposeful (i.e., as the result of a systematic search) discoveries. Another motivation was the possibility of discerning useful clues how to search more efficiently for such objects. There are 60 minor planets in the sample. The principal result is that the discovery of Earth-approaching asteroids is dominated by serendipity. Therefore, searching for them at the current relatively bright limits at less than a very high rate seems pointless
Brane in 6D with increasing gravitational trapping potential
A new solution to Einstein equations in (1+5)-spacetime with an embedded
(1+3) brane is given. This solution localizes the zero modes of all kinds of
matter fields and 4-gravity on the (1+3) brane by an increasing, transverse
gravitational potential. This localization occurs despite the fact that the
gravitational potential is not a decreasing exponential, and asymptotically
approaches a finite value rather than zero.Comment: Revised paper. 6 pages, revtex 4. to be published in PR
Scalar field localization on a brane with cosmological constant
We address the localization of a scalar field, whose bulk-mass M is
considered in a wide range including the tachyonic region,on a three-brane. The
brane with non-zero cosmological constant is embedded in five
dimensional bulk space. We find in this case that the trapped scalar could have
mass which has an upper bound and expressed as with the calculable numbers . We point
out that this result would be important to study the stability of the brane and
cosmological problems based on the brane-world.Comment: 14 pages, 5 figure
Series solutions for a static scalar potential in a Salam-Sezgin Supergravitational hybrid braneworld
The static potential for a massless scalar field shares the essential
features of the scalar gravitational mode in a tensorial perturbation analysis
about the background solution. Using the fluxbrane construction of [8] we
calculate the lowest order of the static potential of a massless scalar field
on a thin brane using series solutions to the scalar field's Klein Gordon
equation and we find that it has the same form as Newton's Law of Gravity. We
claim our method will in general provide a quick and useful check that one may
use to see if their model will recover Newton's Law to lowest order on the
brane.Comment: 5 pages, no figure
The Randall-Sundrum Scenario with an Extra Warped Dimension
We investigate a scenario with two four-branes embedded in six dimensions.
When the metric is periodic and compact in one of the dimensions parallel to
the branes, the value of the effective cosmological constant for the remaining
five dimensions can assume a variety of values, determined by the dependence of
the metric on the sixth dimension. The picture that emerges resembles the
Randall-Sundrum model but with an extra warped dimension that allows the usual
brane-bulk fine tuning to be satisfied without finely tuning any of the
parameters in the underlying six dimensional theory. Although the action
contains terms with four derivatives of the metric, we show that when the
branes have a finite, natural thickness, such terms have only a small effect on
the Randall-Sundrum structure. The presence of these four derivative terms also
allows a configuration that resembles that produced by a domain wall but which
results from gravity alone.Comment: 12 pages, 3 figures, requires harvmac and picte
Wave function of the radion in a brane world
We calculate the linearized metric perturbation corresponding to a massless
four-dimensional scalar field, the radion, in a five-dimensional two-brane
model of Randall and Sundrum. In this way we obtain relative strengths of the
radion couplings to matter residing on each of the branes. The results are in
agreement with the analysis of Garriga and Tanaka of gravitational and
Brans--Dicke forces between matter on the branes. We also introduce a model
with infinite fifth dimension and ``almost'' confined graviton, and calculate
the radion properties in that model.Comment: 5 pages revtex, no figures, equation correcte
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