131 research outputs found
A Microscopic Model for the Black hole - Black string Phase Transition
Computations in general relativity have revealed an interesting phase diagram for the black hole - black string phase transition, with three different black objects present for a range of mass values. We can add charges to this system by `boosting' plus dualities; this makes only kinematic changes in the gravity computation but has the virtue of bringing the system into the near-extremal domain where a microscopic model can be conjectured. When the compactification radius is very large or very small then we get the microscopic models of 4+1 dimensional near-extremal holes and 3+1 dimensional near-extremal holes respectively (the latter is a uniform black string in 4+1 dimensions). We propose a simple model that interpolates between these limits and reproduces most of the features of the phase diagram. These results should help us understand how `fractionation' of branes works in general situations
The information paradox: A pedagogical introduction
The black hole information paradox is a very poorly understood problem. It is
often believed that Hawking's argument is not precisely formulated, and a more
careful accounting of naturally occurring quantum corrections will allow the
radiation process to become unitary. We show that such is not the case, by
proving that small corrections to the leading order Hawking computation cannot
remove the entanglement between the radiation and the hole. We formulate
Hawking's argument as a `theorem': assuming `traditional' physics at the
horizon and usual assumptions of locality we will be forced into mixed states
or remnants. We also argue that one cannot explain away the problem by invoking
AdS/CFT duality. We conclude with recent results on the quantum physics of
black holes which show the the interior of black holes have a `fuzzball'
structure. This nontrivial structure of microstates resolves the information
paradox, and gives a qualitative picture of how classical intuition can break
down in black hole physics.Comment: 38 pages, 7 figures, Latex (Expanded form of lectures given at CERN
for the RTN Winter School, Feb 09), typo correcte
Black holes and holography
The idea of holography in gravity arose from the fact that the entropy of
black holes is given by their surface area. The holography encountered in
gauge/gravity duality has no such relation however; the boundary surface can be
placed at an arbitrary location in AdS space and its area does not give the
entropy of the bulk. The essential issues are also different between the two
cases: in black holes we get Hawking radiation from the `holographic surface'
which leads to the information issue, while in gauge/gravity duality there is
no such radiation from the boundary surface. To resolve the information paradox
we need to show that there are real degrees of freedom at the horizon of the
hole; this is achieved by the fuzzball construction. While the fuzzball has no
interior to the horizon, we argue that an auxiliary spacetime can be
constructed to continue the collective dynamics of fuzzball for times of order
the crossing time; this is an analogue of `complementarity'.Comment: 28 pages, 21 figures, Expanded version of proceedings for COSGRAV12,
Kolkata, Feb 201
Comments on black holes I: The possibility of complementarity
We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who
argue against black hole complementarity based on the claim that an infalling
observer 'burns' as he approaches the horizon. We show that in fact
measurements made by an infalling observer outside the horizon are
statistically identical for the cases of vacuum at the horizon and radiation
emerging from a stretched horizon. This forces us to follow the dynamics all
the way to the horizon, where we need to know the details of Planck scale
physics. We note that in string theory the fuzzball structure of microstates
does not give any place to 'continue through' this Planck regime. AMPS argue
that interactions near the horizon preclude traditional complementarity. But
the conjecture of 'fuzzball complementarity' works in the opposite way: the
infalling quantum is absorbed by the fuzzball surface, and it is the resulting
dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde
Pair creation in non-extremal fuzzball geometries
It is possible to construct a special family of nonextremal black hole
microstates. These microstates are unstable, and emit radiation at a rate which
is found to exactly equal the Hawking radiation rate predicted for them by the
dual CFT. In this paper we analyze in more detail the nature of the radiation
created by these unstable modes. The energy and angular momentum of the mode is
found to be localized in two regions: one near infinity corresponding to the
emitted quanta, and the other in the ergoregion which is deep inside the
interior of the geometry. The energy and angular momenta are equal and opposite
for these two contributions, as expected for emission from ergoregions. We
conjecture that more general nonextremal microstates will possess ergoregions
(with no axial symmetry), and radiation from these regions can be part of the
general Hawking emission for the microstates.Comment: added references, corrected typo
Black Holes as Effective Geometries
Gravitational entropy arises in string theory via coarse graining over an
underlying space of microstates. In this review we would like to address the
question of how the classical black hole geometry itself arises as an effective
or approximate description of a pure state, in a closed string theory, which
semiclassical observers are unable to distinguish from the "naive" geometry. In
cases with enough supersymmetry it has been possible to explicitly construct
these microstates in spacetime, and understand how coarse-graining of
non-singular, horizon-free objects can lead to an effective description as an
extremal black hole. We discuss how these results arise for examples in Type II
string theory on AdS_5 x S^5 and on AdS_3 x S^3 x T^4 that preserve 16 and 8
supercharges respectively. For such a picture of black holes as effective
geometries to extend to cases with finite horizon area the scale of quantum
effects in gravity would have to extend well beyond the vicinity of the
singularities in the effective theory. By studying examples in M-theory on
AdS_3 x S^2 x CY that preserve 4 supersymmetries we show how this can happen.Comment: Review based on lectures of JdB at CERN RTN Winter School and of VB
at PIMS Summer School. 68 pages. Added reference
Fractional Brane State in the Early Universe
In the early Universe matter was crushed to high densities, in a manner
similar to that encountered in gravitational collapse to black holes. String
theory suggests that the large entropy of black holes can be understood in
terms of fractional branes and antibranes. We assume a similar physics for the
matter in the early Universe, taking a toroidal compactification and letting
branes wrap around the cycles of the torus. We find an equation of state
p_i=w_i rho, for which the dynamics can be solved analytically. For black
holes, fractionation can lead to non-local quantum gravity effects across
length scales of order the horizon radius; similar effects in the early
Universe might change our understanding of Cosmology in basic ways.Comment: 40 pages, 18 figures, references adde
Non-extremal Black Hole Microstates: Fuzzballs of Fire or Fuzzballs of Fuzz ?
We construct the first family of microstate geometries of near-extremal black
holes, by placing metastable supertubes inside certain scaling supersymmetric
smooth microstate geometries. These fuzzballs differ from the classical black
hole solution macroscopically at the horizon scale, and for certain probes the
fluctuations between various fuzzballs will be visible as thermal noise far
away from the horizon. We discuss whether these fuzzballs appear to infalling
observers as fuzzballs of fuzz or as fuzzballs of fire. The existence of these
solutions suggests that the singularity of non-extremal black holes is resolved
all the way to the outer horizon and this "backwards in time" singularity
resolution can shed light on the resolution of spacelike cosmological
singularities.Comment: 34 pages, 10 figure
The Nuts and Bolts of Einstein-Maxwell Solutions
We find new non-supersymmetric solutions of five-dimensional ungauged
supergravity coupled to two vector multiplets. The solutions are regular,
horizonless and have the same asymptotic charges as non-extremal charged black
holes. An essential ingredient in our construction is a four-dimensional
Euclidean base which is a solution to Einstein-Maxwell equations. We construct
stationary solutions based on the Euclidean dyonic Reissner-Nordstrom black
hole as well as a six-parameter family with a dyonic Kerr-Newman-NUT base.
These solutions can be viewed as compactifications of eleven-dimensional
supergravity on a six-torus and we discuss their brane interpretation.Comment: 29 pages, 3 figure
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