6,051 research outputs found
Cosmology and matter induced branes
The extra space paradigm plays a significant role in modern physics and in
cosmology as the specific case. In this review, the relation between the main
cosmological parameters - Planck mass and Cosmological constants - and a metric
of extra space is discussed. Matter distribution inside extra space and its
effect on the 4-dimensional observational parameters is of particular interest.
The ways to solve the Fine-tuning problem and the Hierarchy problem are
analyzed.Comment: 23 pages, 2 figure
Gauss-Bonnet Brane Cosmology with Radion Stabilization
We study cosmology in a five-dimensional brane-world with a stabilizing
effective potential for the radion and matter localized on the two branes. We
consider the corrections induced by the Gauss-Bonnet contribution to the total
action performing and expansion around the two possible static solutions up to
second order in the ratio between brane matter energy density and brane
tensions. The Friedmann and acceleration equations on the visible brane are
obtained and discussed.Comment: To be published in Phys.Rev.D, References Adde
Cosmology in Six Dimensions
We discuss cosmological models in six-dimensional spacetime. For
codimension-1 branes, we consider a (4+1) braneworld model and discuss its
cosmological evolution. For codimension-2 branes, we consider an infinitely
thin conical braneword model in the presence of an induced gravity term on the
brane and a Gauss-Bonnet term in the bulk. We discuss the cosmological
evolution of isotropic and anisotropic matter on the brane. We also briefly
discuss cosmological models in six-dimensional supergravity.Comment: 18 pages, 1 figure, plenary talk at 100 Years of Relativity:
International Conference on Classical and Quantum Aspects of Gravity and
Cosmology, Sao Paulo, Brazil, 22-24 August 200
AdS/CFT and gravity
The radiation-dominated k=0 FRW cosmology emerges as the induced metric on a
codimension one hypersurface of constant extrinsic curvature in the
five-dimensional AdS-Schwarzschild solution. That we should get FRW cosmology
in this way is an expected result from AdS/CFT in light of recent comments
regarding the coupling of gravity to "boundary" conformal field theories. I
remark on how this calculation bears on the understanding of Randall and
Sundrum's "alternative to compactification." A generalization of the AdS/CFT
prescription for computing Green's functions is suggested, and it is shown how
gravity emerges from it with a strength G_4 = 2 G_5/L. Some numerical bounds
are set on the radius of curvature L of AdS_5. One of them comes from
estimating the rate of leakage of visible sector energy into the CFT. That rate
is connected via a unitarity relation to deviations from Newton's force law at
short distances. The best bound on L obtained in this paper comes from a match
to the parameters of string theory. It is L < 1 nm if the string scale is 1
GeV. Higher string scales imply a tighter bound on L.Comment: 27 pages, two figures, latex. v2: No log in first correction to
Newton's law! Refs added, other minor improvements. v3: Refinements and
further ref
On Bouncing Brane-Worlds, S-branes and Branonium Cosmology
We present several higher-dimensional spacetimes for which observers living
on 3-branes experience an induced metric which bounces. The classes of examples
include boundary branes on generalised S-brane backgrounds and probe branes in
D-brane/anti D-brane systems. The bounces we consider normally would be
expected to require an energy density which violates the weak energy condition,
and for our co-dimension one examples this is attributable to bulk curvature
terms in the effective Friedmann equation. We examine the features of the
acceleration which provides the bounce, including in some cases the existence
of positive acceleration without event horizons, and we give a geometrical
interpretation for it. We discuss the stability of the solutions from the point
of view of both the brane and the bulk. Some of our examples appear to be
stable from the bulk point of view, suggesting the possible existence of stable
bouncing cosmologies within the brane-world framework.Comment: 35 pages, 7 figures, JHEP style. Title changed and references adde
Some Aspects of String Cosmology and the LHC
I discuss some (unconventional) aspects of String Cosmology of relevance to
supersymmetric dark matter searches at the Large Hadron Collider (LHC) at CERN.
In particular, I analyse the role of time-dependent dilaton fields in relaxing
some of the stringent constraints that characterise minimal supersymmetric
models in standard cosmology. I also study briefly CPT-violating aspects of
brane Universe models with space-time brane defects at early epochs and their
potential relevance to the observed Baryon Asymmetry.Comment: 12 pages pdflatex, uses special macros.Plenary talk at the 1st
International Conference on New Frontiers in Physics 2012, Kolymbari (Crete,
Greece), June 10-16 2012, to appear in the Proc. EPJ WEB of Conferences,
updated reference
Radion Potential and Brane Dynamics
We examine the cosmology of the Randall-Sundrum model in a dynamic setting
where scalar fields are present in the bulk as well as the branes. This
generates a mechanism similar to that of Goldberger-Wise for radion
stabilization and the recovery of late-cosmology features in the branes. Due to
the induced radion dynamics, the inflating branes roll towards the minimum of
the radion potential, thereby exiting inflation and reheating the Universe. In
the slow roll part of the potential, the 'TeV' branes have maximum inflation
rate and energy as their coupling to the radion and bulk modes have minimum
suppresion. Hence, when rolling down the steep end of the potential towards the
stable point, the radion field (which appears as the inflaton of the effective
4D theory in the branes) decays very fast, reheats the Universe .This process
results decayin a decrease of brane's canonical vacuum energy .
However, at the minimum of the potential is small but not
neccessarily zero and the fine-tuning issue remains .Density perturbation
constraints introduce an upper bound when the radion stabilizies. Due to the
large radion mass and strong suppression to the bulk modes, moduli problems and
bulk reheating do not occur. The reheat temperature and a sufficient number of
e-folding constraints for the brane-universe are also satisfied. The model
therefore recovers the radiation dominated FRW universe.Comment: 16 pages, 3 figures,extraneous sentences removed, 2 footnotes added,
some typos correcte
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