841 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 $many$ $inflating$
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

### Brane Induced Gravity: Codimension-2

We review the results of arXiv:hep-th/0703190, on brane induced gravity (BIG)
in 6D. Among a large diversity of regulated codimension-2 branes, we find that
for near-critical tensions branes live inside very deep throats which
efficiently compactify the angular dimension. In there, 4D gravity first
changes to 5D, and only later to 6D. The crossover from 4D to 5D is independent
of the tension, but the crossover from 5D to 6D is not. This shows how the
vacuum energy problem manifests in BIG: instead of tuning vacuum energy to
adjust the 4D curvature, generically one must tune it to get the desired
crossover scales and the hierarchy between the scales governing the 4D \to 5D
\to 6D transitions. In the near-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: 16 pages latex, 2 .eps figs, based on the talks given at the "Sowers
Workshop", Virginia Tech, May 14-18, 2007, "Cosmology and Strings" workshop
at ICTP, Trieste, Italy, July 9-13, 2007, "Dark Energy In the Universe",
Hakone, Japan, Sep 1-4, 2007 and "Zagreb Workshop 2007", Zagreb, Croatia, Nov
9-11, 2007; v2: added reference

### Infinitely Large New Dimensions

We construct intersecting brane configurations in Anti-de-Sitter space
localizing gravity to the intersection region, with any number $n$ 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 $M_{Pl}$ is determined in
terms of the fundamental Planck scale $M_*$ and the $AdS$ radius of curvature
$L$ via the familiar relation $M_{Pl}^2 \sim M_{*}^{2+n} L^n$; $L$ acts as an
effective radius of compactification for gravity on the intersection. Taking
$M_* \sim$ TeV and $L \sim$ sub-mm reproduces the phenomenology of theories
with large extra dimensions. Alternately, taking $M_* \sim L^{-1} \sim M_{Pl}$,
and placing our 3-brane a distance $\sim 100 M_{Pl}^{-1}$ 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 $\times$
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 $5D$, and only later to $6D$. 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

### Origami World

We paste together patches of $AdS_6$ to find solutions which describe two
4-branes intersecting on a 3-brane with non-zero tension. We construct
explicitly brane arrays with Minkowski, de Sitter and Anti-de Sitter geometries
intrinsic to the 3-brane, and describe how to generalize these solutions to the
case of $AdS_{4+n}$, $n>2$, where $n$ $n+2$-branes intersect on a 3-brane. The
Minkowski and de Sitter solutions localize gravity to the intersection, leading
to 4D Newtonian gravity at large distances. We show this explicitly in the case
of Minkowski origami by finding the zero-mode graviton, and computing the
couplings of the bulk gravitons to the matter on the intersection. In de Sitter
case, this follows from the finiteness of the bulk volume. The effective 4D
Planck scale depends on the square of the fundamental 6D Planck scale, the
$AdS_6$ radius and the angles between the 4-branes and the radial $AdS$
direction, and for the Minkowski origami it is $M_4{}^2 = {2/3} \Bigl(\tan
\alpha_1 + \tan \alpha_2 \Bigr) M_*{}^4 L^2$. If $M_* \sim {\rm few} \times
TeV$ this may account for the Planck-electroweak hierarchy even if $L \sim
10^{-4} {\rm m}$, with a possibility for sub-millimeter corrections to the
Newton's law. We comment on the early universe cosmology of such models.Comment: plain LaTeX, 23 pages + 2 .eps figure

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