615 research outputs found
The Action of Instantons with Nut Charge
We examine the effect of a non-trivial nut charge on the action of
non-compact four-dimensional instantons with a U(1) isometry. If the instanton
action is calculated by dimensionally reducing along the isometry, then the nut
charge is found to make an explicit non-zero contribution. For metrics
satisfying AF, ALF or ALE boundary conditions, the action can be expressed
entirely in terms of quantities (including the nut charge) defined on the fixed
point set of the isometry. A source (or sink) of nut charge also implies the
presence of a Misner string coordinate singularity, which will have an
important effect on the Hamiltonian of the instanton.Comment: 25 page
Information Loss in Black Holes
The question of whether information is lost in black holes is investigated
using Euclidean path integrals. The formation and evaporation of black holes is
regarded as a scattering problem with all measurements being made at infinity.
This seems to be well formulated only in asymptotically AdS spacetimes. The
path integral over metrics with trivial topology is unitary and information
preserving. On the other hand, the path integral over metrics with non-trivial
topologies leads to correlation functions that decay to zero. Thus at late
times only the unitary information preserving path integrals over trivial
topologies will contribute. Elementary quantum gravity interactions do not lose
information or quantum coherence
A Secret Tunnel Through The Horizon
Hawking radiation is often intuitively visualized as particles that have
tunneled across the horizon. Yet, at first sight, it is not apparent where the
barrier is. Here I show that the barrier depends on the tunneling particle
itself. The key is to implement energy conservation, so that the black hole
contracts during the process of radiation. A direct consequence is that the
radiation spectrum cannot be strictly thermal. The correction to the thermal
spectrum is of precisely the form that one would expect from an underlying
unitary quantum theory. This may have profound implications for the black hole
information puzzle.Comment: First prize in the Gravity Research Foundation Essay Competition. 7
pages, LaTe
Generalized entropy and Noether charge
We find an expression for the generalized gravitational entropy of Hawking in
terms of Noether charge. As an example, the entropy of the Taub-Bolt spacetime
is calculated.Comment: 6 pages, revtex, reference correcte
AdS3 Gravitational Instantons from Conformal Field Theory
A conformal field theory on the boundary of three-dimensional asymptotic
anti-de Sitter spaces which appear as near horizon geometry of D-brane bound
states is discussed. It is shown that partition functions of gravitational
instantons appear as high and low temperature limits of the partition function
of the conformal field theory. The result reproduces phase transition between
the anti-de Sitter space and the BTZ black hole in the bulk gravity.Comment: 22 pages, minor correction
Dynamic and Thermodynamic Stability and Negative Modes in Schwarzschild-Anti-de Sitter
The thermodynamic properties of Schwarzschild-anti-de Sitter black holes
confined within finite isothermal cavities are examined. In contrast to the
Schwarzschild case, the infinite cavity limit may be taken which, if suitably
stated, remains double valued. This allows the correspondence between
non-existence of negative modes for classical solutions and local thermodynamic
stability of the equilibrium configuration of such solutions to be shown in a
well defined manner. This is not possible in the asymptotically flat case.
Furthermore, the non-existence of negative modes for the larger black hole
solution in Schwarzschild-anti-de Sitter provides strong evidence in favour of
the recent positive energy conjecture by Horowitz and Myers.Comment: 21 pages, 5 figures, LaTe
Gravitational Entropy and Global Structure
The underlying reason for the existence of gravitational entropy is traced to
the impossibility of foliating topologically non-trivial Euclidean spacetimes
with a time function to give a unitary Hamiltonian evolution. In dimensions
the entropy can be expressed in terms of the obstructions to foliation,
bolts and Misner strings, by a universal formula. We illustrate with a number
of examples including spaces with nut charge. In these cases, the entropy is
not just a quarter the area of the bolt, as it is for black holes.Comment: 18 pages. References adde
Entanglement entropy of the black hole horizon
We examine a possibility that, when a black hole is formed, the information
on the collapsed star is stored as the entanglement entropy between the outside
and the thin region (of the order of the Planck length) of the inside the
horizon. For this reason, we call this as the entanglement entropy of the black
hole ``horizon''. We construct two models, one is in the Minkowski spacetime
and the other is in the Rindler wedge. To calculate the entropy explicitly, we
assume that the thin regions of the order of the Planck length of the outside
and inside the horizon are completely entangled by quantum effects. We also use
a property of the entanglement entropy that it is symmetric under an
interchange of the observed and unobserved subsystems. Our setting and this
symmetric property substantially reduce the needed numerical calculation. As a
result of our analysis, we can explain the Bekenstein-Hawking entropy itself
(rather than its correction by matter fields) in the context of the
entanglement entropy.Comment: 28 pages, 5 figures, section 1 and the paragraph before subsection
3.1 are improved and enlarge
Entropy of Rotating Misner String Spacetimes
Using a boundary counterterm prescription motivated by the AdS/CFT
conjecture, I evaluate the energy, entropy and angular momentum of the class of
Kerr-NUT/bolt-AdS spacetimes. As in the non-rotating case, when the NUT charge
is nonzero the entropy is no longer equal to one-quarter of the area due to the
presence of the Misner string. When the cosmological constant is also non-zero,
the entropy is bounded from above.Comment: Revtex, 9 pages, 3 figure
A Note on the Generalization of the GEMS Approach
This paper is a supplement of our earlier work JHEP 0410 (2004)
011[gr-qc/0409107].We map the vector potential of charged black holes into GEMS
and find that its effect on the thermal spectrum is the same as that on the
black hole side, i.e., it will induce a chemical potential in the thermal
spectrum which is the same as that in the charged black holes.We also argue
that the generalization of GEMS approach to non-stationary motions is not
possible.Comment: Latex file, 10 pages, no figure; v2: minor corrections; v3: revised
with title changed, one new section added and references adde
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