325 research outputs found
Typicality versus thermality: An analytic distinction
In systems with a large degeneracy of states such as black holes, one expects
that the average value of probe correlation functions will be well approximated
by the thermal ensemble. To understand how correlation functions in individual
microstates differ from the canonical ensemble average and from each other, we
study the variances in correlators. Using general statistical considerations,
we show that the variance between microstates will be exponentially suppressed
in the entropy. However, by exploiting the analytic properties of correlation
functions we argue that these variances are amplified in imaginary time,
thereby distinguishing pure states from the thermal density matrix. We
demonstrate our general results in specific examples and argue that our results
apply to the microstates of black holes.Comment: 22 pages + appendices, 3 eps figure
General 2 charge geometries
Two charge BPS horizon free supergravity geometries are important in
proposals for understanding black hole microstates. In this paper we construct
a new class of geometries in the NS1-P system, corresponding to solitonic
strings carrying fermionic as well as bosonic condensates. Such geometries are
required to account for the full microscopic entropy of the NS1-P system. We
then briefly discuss the properties of the corresponding geometries in the dual
D1-D5 system.Comment: 44 page
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
1/4-BPS M-theory bubbles with SO(3) x SO(4) symmetry
In this paper we generalize the work of Lin, Lunin and Maldacena on the
classification of 1/2-BPS M-theory solutions to a specific class of 1/4-BPS
configurations. We are interested in the solutions of 11 dimensional
supergravity with symmetry, and it is shown that such
solutions are constructed over a one-parameter familiy of 4 dimensional almost
Calabi-Yau spaces. Through analytic continuations we can obtain M-theory
solutions having or factors. It is shown
that our result is equivalent to the solutions which have been recently
reported as the near-horizon geometry of M2 or M5-branes wrapped on 2 or
4-cycles in Calabi-Yau threefolds. We also discuss the hierarchy of M-theory
bubbles with different number of supersymmetries.Comment: 22 pages, JHEP3.cls; v2. revised version. showed that our results
agree with previous works hep-th/0605146 and hep-th/061219
Very Long Time Scales and Black Hole Thermal Equilibrium
We estimate the very long time behaviour of correlation functions in the
presence of eternal black holes. It was pointed out by Maldacena (hep-th
0106112) that their vanishing would lead to a violation of a unitarity-based
bound. The value of the bound is obtained from the holographic dual field
theory. The correlators indeed vanish in a semiclassical bulk approximation. We
trace the origin of their vanishing to the continuum energy spectrum in the
presence of event horizons. We elaborate on the two very long time scales
involved: one associated with the black hole and the other with a thermal gas
in the vacuum background. We find that assigning a role to the thermal gas
background, as suggested in the above work, does restore the compliance with a
time-averaged unitarity bound. We also find that additional configurations are
needed to explain the expected time dependence of the Poincar\'e recurrences
and their magnitude. It is suggested that, while a semiclassical black hole
does reproduce faithfully ``coarse grained'' properties of the system,
additional dynamical features of the horizon may be necessary to resolve a
finer grained information-loss problem. In particular, an effectively formed
stretched horizon could yield the desired results.Comment: 30 pages, harvmac, 1 eps figur
Spacetime in String Theory
We give a brief overview of the nature of spacetime emerging from string
theory. This is radically different from the familiar spacetime of Einstein's
relativity. At a perturbative level, the spacetime metric appears as ``coupling
constants" in a two dimensional quantum field theory. Nonperturbatively (with
certain boundary conditions), spacetime is not fundamental but must be
reconstructed from a holographic, dual theory.Comment: 20 pages; references adde
A solution of the coincidence problem based on the recent galactic core black hole mass density increase
A mechanism capable to provide a natural solution to two major cosmological
problems, i.e. the cosmic acceleration and the coincidence problem, is
proposed. A specific brane-bulk energy exchange mechanism produces a total dark
pressure, arising when adding all normal to the brane negative pressures in the
interior of galactic core black holes. This astrophysically produced negative
dark pressure explains cosmic acceleration and why the dark energy today is of
the same order to the matter density for a wide range of the involved
parameters. An exciting result of the analysis is that the recent rise of the
galactic core black hole mass density causes the recent passage from cosmic
deceleration to acceleration. Finally, it is worth mentioning that this work
corrects a wide spread fallacy among brane cosmologists, i.e. that escaping
gravitons result to positive dark pressure.Comment: 14 pages, 3 figure
On the existence of supergravity duals to D1--D5 CFT states
We define a metric operator in the 1/2-BPS sector of the D1-D5 CFT, the
eigenstates of which have a good semi-classical supergravity dual; the
non-eigenstates cannot be mapped to semi-classical gravity duals. We also
analyse how the data defining a CFT state manifests itself in the gravity side,
and show that it is arranged into a set of multipoles. Interestingly, we find
that quantum mechanical interference in the CFT can have observable
manifestations in the semi-classical gravity dual. We also point out that the
multipoles associated to the normal statistical ensemble fluctuate wildly,
indicating that the mixed thermal state should not be associated to a
semi-classical geometry.Comment: 22 pages, 2 figures. v2 : references added, typos correcte
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
The influence of D-branes' backreaction upon gravitational interactions between open strings
We argue that gravitational interactions between open strings ending on
D3-branes are largely shaped by the D3-branes' backreaction. To this end we
consider classical open strings coupled to general relativity in Poincare AdS5
backgrounds. We compute the linear gravitational backreaction of a static
string extending up to the Poincare horizon, and deduce the potential energy
between two such strings. If spacetime is non-compact, we find that the
gravitational potential energy between parallel open strings is independent of
the strings' inertial masses and goes like 1/r at large distance r. If the
space transverse to the D3-branes is suitably compactified, a collective mode
of the graviton propagates usual four-dimensional gravity. In that case the
backreaction of the D3-branes induces a correction to the Newtonian potential
energy that violates the equivalence principle. The observed enhancement of the
gravitational attraction is specific to string theory; there is no similar
effect for point-particles.Comment: 28 pages, 7 figures. Typos corrected, minor addition
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