7 research outputs found
Information locking in black holes
The black hole information loss paradox has plagued physicists since
Hawking's discovery that black holes evaporate thermally in contradiction to
the unitarity expected by quantum mechanics. Here we show that one of the
central presumptions of the debate is incorrect. Ensuring that information not
escape during the semi-classical evaporation process does not require that all
the information remain in the black hole until the final stages of evaporation.
Using recent results in quantum information theory, we find that the amount of
information that must remain in the black hole until the final stages of
evaporation can be very small, even though the amount already radiated away is
negligible. Quantum effects mean that information need not be additive: a small
number of quanta can lock a large amount of information, making it
inaccessible. When this small number of locking quanta are finally emitted, the
full information (and unitarity) is restored. Only if the number of initial
states is restricted will the locking mechanism leak out information early.Comment: 5 pages, to appear in PRL. Presented at the Newton Institute's
workshop on Quantum gravity and quantum information, Dec. 17th, 200
Exact Black Holes and Gravitational Shockwaves on Codimension-2 Branes
We derive exact gravitational fields of a black hole and a relativistic
particle stuck on a codimension-2 brane in dimensions when gravity is ruled
by the bulk -dimensional Einstein-Hilbert action. The black hole is locally
the higher-dimensional Schwarzschild solution, which is threaded by a tensional
brane yielding a deficit angle and includes the first explicit example of a
`small' black hole on a tensional 3-brane. The shockwaves allow us to study the
large distance limits of gravity on codimension-2 branes. In an infinite
locally flat bulk, they extinguish as , i.e. as on a 3-brane
in , manifestly displaying the full dimensionality of spacetime. We check
that when we compactify the bulk, this special case correctly reduces to the 4D
Aichelburg-Sexl solution at large distances. Our examples show that gravity
does not really obstruct having general matter stress-energy on codimension-2
branes, although its mathematical description may be more involved.Comment: 18 pages, LaTeX; v2: added references, version to appear in JHE
Cosmic Acceleration Driven by Mirage Inhomogeneities
A cosmological model based on an inhomogeneous D3-brane moving in an AdS_5 X
S_5 bulk is introduced. Although there is no special points in the bulk, the
brane Universe has a center and is isotropic around it. The model has an
accelerating expansion and its effective cosmological constant is inversely
proportional to the distance from the center, giving a possible geometrical
origin for the smallness of a present-day cosmological constant. Besides, if
our model is considered as an alternative of early time acceleration, it is
shown that the early stage accelerating phase ends in a dust dominated FRW
homogeneous Universe. Mirage-driven acceleration thus provides a dark matter
component for the brane Universe final state. We finally show that the model
fulfills the current constraints on inhomogeneities.Comment: 14 pages, 1 figure, IOP style. v2, changed style, minor corrections,
references added, version accepted in Class. Quant. Gra
Particle motion and gravitational lensing in the metric of a dilaton black hole in a de Sitter universe
We consider the metric exterior to a charged dilaton black hole in a de
Sitter universe. We study the motion of a test particle in this metric.
Conserved quantities are identified and the Hamilton-Jacobi method is employed
for the solutions of the equations of motion. At large distances from the black
hole the Hubble expansion of the universe modifies the effective potential such
that bound orbits could exist up to an upper limit of the angular momentum per
mass for the orbiting test particle. We then study the phenomenon of strong
field gravitational lensing by these black holes by extending the standard
formalism of strong lensing to the non-asymptotically flat dilaton-de Sitter
metric. Expressions for the various lensing quantities are obtained in terms of
the metric coefficients.Comment: 8 pages, RevTex, 1 eps figures; discussion improved; typos corrected;
references adde
The Cosmological Slingshot Scenario: A Stringy Early Times Universe
A cosmological model for the early time Universe is proposed. In this model,
the Universe is a wandering brane moving in a warped throat of a Calabi-Yau
space. A non-zero angular momentum induces a turning point in the brane
trajectory, and leads to a bouncing cosmology as experienced by an observer
living on the brane. The Universe undergoes a decelerated contraction followed
by an accelerating expansion and no big-bang singularity. Although the number
of e-folds of accelerated motion is low (less than 2), standard cosmological
problems are not present in our model thanks to the absence of an initial
singularity and the violation of energy conditions of mirage matter at high
energies. Density perturbations are also calculated in our model and we find a
slightly red spectral index with negligible tensorial perturbations in
compatibility with WMAP data.Comment: v5: clarifications and references added, results unchanged, version
accepted in Class. Quant. Grav. (2008), 34 pages, 5 figure
The Cosmological Slingshot Scenario: Myths and Facts
We generalize the Cosmological Slingshot Scenario for a Slingshot brane
moving in a Klebanov-Strassler throat. We show that the horizon and isotropy
problems of standard cosmology are avoided, while the flatness problem is
acceptably alleviated. Regarding the primordial perturbations, we identify
their vacuum state and elucidate the evolution from the quantum to the
classical regimes. Also, we calculate their exact power spectrum showing its
compatibility with current data. We discuss the bouncing solution from a four
dimensional point of view. In this framework the radial and angular motion of
the Slingshot brane are described by two scalar fields. We show that the
bouncing solution for the scale factor in String frame is mapped into a
monotonically increasing (in conformal time) solution in the Einstein frame. We
finally discuss about the regularity of the geometry in Einstein frame.Comment: 16 pages, 2 figs. Major clarifications and references added, version
accepted in Gen. Rel. Grav. (2009
Hawking Radiation from Higher-Dimensional Black Holes
We review the quantum field theory description of Hawking radiation from evaporating black holes and summarize what is known about Hawking radiation from black holes in more than four space-time dimensions. In the context of the Large Extra Dimensions scenario, we present the theoretical formalism for all types of emitted fields and a selection of results on the radiation spectra. A detailed analysis of the Hawking fluxes in this case is essential for modelling the evaporation of higher-dimensional black holes at the LHC, whose creation is predicted by low-energy models of quantum gravity. We discuss the status of the quest for black-hole solutions in the context of the Randall-Sundrum brane-world model and, in the absence of an exact metric, we review what is known about Hawking radiation from such black holes