731 research outputs found
Rotating Black Holes on Codimension-2 Branes
It has recently been demonstrated that certain types of non-tensional
stress-energy can live on tensional codimension-2 branes, including
gravitational shockwaves and small Schwarzschild black holes. In this note we
generalize the earlier Schwarzschild results, and construct the exact
gravitational fields of small rotating black holes on a codimension-2 brane. We
focus on the phenomenologically interesting case of a three-brane embedded in a
spacetime with two compactified extra dimensions. For a nonzero tension on the
brane, we verify that these solutions also show the ``lightning rod'' effect
found in the Schwarzschild solutions, the net effect of which is to rescale the
fundamental Planck mass. This allows for larger black hole parameters, such as
the event horizon, angular momentum, and lifetime than would be naively
expected for a tensionless brane. It is also found that a black hole with
angular momentum pointing purely along the brane directions has a smaller
horizon angular velocity than the corresponding tensionless case, while a hole
with bulk components of angular momentum has a larger angular velocity.Comment: 7 pages, uses revte
Decaying Cosmological Constant of the Inflating Branes in the Randall-Sundrum -Oda Model
We examine the issue of the cosmological constant in the
branes scenario, extending on two recent models by I.Oda and Randall-Sundrum.
The exact solution in a closed form is found in the slow roll approximation of
the radion. Defining an effective expansion rate, which depends on the location
of each brane in the fifth dimension and demanding stability for this case we
show that each positive tension brane has a localized, decaying cosmological
constant (the opposite process applies to the negative energy branes [4]) . The
reason is that the square of the effective expansion rate enters as a source
term in the Einstein equations for the branes.Thus the brane has two scale
factors depending on time and the fifth dimnesion respectively .The brane will
roll along the fifth dimension in order to readjust its effective expansion
rate in such a way that it compensates for its internal energy changes due to
inflation and possible phase transitions.Comment: 9 pages, comments and ref.added, solution replaced with the exact
one, submitted to PR
Infinitely Large New Dimensions
We construct intersecting brane configurations in Anti-de-Sitter space
localizing gravity to the intersection region, with any number of extra
dimensions. This allows us to construct two kinds of theories with infinitely
large new dimensions, TeV scale quantum gravity and sub-millimeter deviations
from Newton's Law. The effective 4D Planck scale is determined in
terms of the fundamental Planck scale and the radius of curvature
via the familiar relation ; acts as an
effective radius of compactification for gravity on the intersection. Taking
TeV and sub-mm reproduces the phenomenology of theories
with large extra dimensions. Alternately, taking ,
and placing our 3-brane a distance away from the
intersection gives us a theory with an exponential determination of the
Weak/Planck hierarchy.Comment: 4 pages, revtex, no figure
Type 0 Brane Inflation from Mirage Cosmology
We consider a three-dimensional brane-universe moving in a Type 0 String
background. The motion induces on the brane a cosmological evolution which, for
some range of the parameters, exhibits an inflationary phase.Comment: 11 pages, latex, one figur
Charting the Landscape of Modified Gravity
We explore brane induced gravity on a 3-brane in six locally flat dimensions.
To regulate the short distance singularities in the brane core, we resolve the
thin brane by a cylindrical 4-brane, with the geometry of 4D Minkowski
a circle, which has an axion flux to cancel the vacuum pressure in the compact
direction. We discover a large diversity of possible solutions controlled by
the axion flux, as governed by its boundary conditions. Hence brane induced
gravity models really give rise to a {\it landscape} of vacua, at least
semiclassically. For sub-critical tensions, the crossover scale, below which
gravity may look 4D, and the effective 4D gravitational coupling are sensitive
to vacuum energy. This shows how the vacuum energy problem manifests in brane
induced gravity: instead of tuning the 4D curvature, generically one must tune
the crossover scale. On the other hand, in the near-critical limit, branes live
inside very deep throats which efficiently compactify the angular dimension. In
there, 4D gravity first changes to , and only later to . The crossover
scale saturates at the gravitational see-saw scale, independent of the tension.
Using the fields of static loops on a wrapped brane, we check the perturbative
description of long range gravity below the crossover scale. In sub-critical
cases the scalars are strongly coupled already at the crossover scale even in
the vacuum, because the brane bending is turned on by the axion flux. Near the
critical limit, linearized perturbation theory remains under control below the
crossover scale, and we find that linearized gravity around the vacuum looks
like a scalar-tensor theory.Comment: 47 LaTeX pages, 3 .eps figures, typos fixed to match the published
versio
Cosmological Solution in M-theory on S^1/Z_2
We provide the first example of a cosmological solution of the Horava-Witten
supergravity. This solution is obtained by exchanging the role of time with the
radial coordinate of the transverse space to the five-brane soliton. On the
boundary this corresponds to rotating an instanton solution into a tunneling
process in a space with Lorentzian signature, leading to an expanding universe.
Due to the freedom to choose different non-trivial Yang-Mills backgrounds on
the boundaries, the two walls of the universe ( visible and hidden worlds)
expand differently. However at late times the anisotropy is washed away by
gravitational interactions.Comment: 10 pages, latex, no figur
A Closer Look at Two Branes in an Bulk
We investigate a scenario with two branes in an bulk. In this
scenario there are two gravitons and we investigate the role played by each of
them for different positions of the second brane. We show that both gravitons
play a significant role only when the turn-around point in the warp factor is
approximately equidistant from both branes. We find that the ultralight mode
becomes heavy as the second brane approaches the turn-around point, and the
physics begins to resemble that of the RS model. Thus we demonstrate the
crucial role played by the turn-around in the warp factor in enabling the
presence of both gravitons.Comment: 21 pages, late
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