4,744 research outputs found
Quantum Coherence in Two Dimensions
The formation and evaporation of two dimensional black holes are discussed.
It is shown that if the radiation in minimal scalars has positive energy, there
must be a global event horizon or a naked singularity. The former would imply
loss of quantum coherence while the latter would lead to an even worse
breakdown of predictability. CPT invariance would suggest that there ought to
be past horizons as well. A way in which this could happen with wormholes is
described.Comment: 11 pages, DAMTP-R93/15, CALT-68-1861, Tex, 3 appended uuencoded
figure
The Superscattering Matrix for Two Dimensional Black Holes
A consistent Euclidean semi classical calculation is given for the
superscattering operator in the RST model for states with a constant flux
of energy. The operator is CPT invariant. There is no loss of quantum
coherence when the energy flux is less than a critical rate and complete loss
when the energy flux is critical.Comment: 12 pages (R/94/4
The Gravitational Hamiltonian in the Presence of Non-Orthogonal Boundaries
This paper generalizes earlier work on Hamiltonian boundary terms by omitting
the requirement that the spacelike hypersurfaces intersect the
timelike boundary orthogonally. The expressions for the action and
Hamiltonian are calculated and the required subtraction of a background
contribution is discussed. The new features of a Hamiltonian formulation with
non-orthogonal boundaries are then illustrated in two examples.Comment: 23 pages, 1 figure, LaTeX. The action is altered to include a corner
term which results in a different value for the non-orthogonal term. An
additional appendix with Euclidean results is included. To appear in Class.
Quant. Gra
Quantum Coherence and Closed Timelike Curves
Various calculations of the matrix have shown that it seems to be non
unitary for interacting fields when there are closed timelike curves. It is
argued that this is because there is loss of quantum coherence caused by the
fact that part of the quantum state circulates on the closed timelike curves
and is not measured at infinity. A prescription is given for calculating the
superscattering matrix on space times whose parameters can be
analytically continued to obtain a Euclidean metric. It is illustrated by a
discussion of a spacetime in with two disks in flat space are identified. If
the disks have an imaginary time separation, this corresponds to a heat bath.
An external field interacting with the heat bath will lose quantum coherence.
One can then analytically continue to an almost real separation of the disks.
This will give closed timelike curves but one will still get loss of quantum
coherence.Comment: 13 page
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
Relationship between Hawking Radiation and Gravitational Anomalies
We show that in order to avoid a breakdown of general covariance at the
quantum level the total flux in each outgoing partial wave of a quantum field
in a black hole background must be equal to that of a (1+1)-dimensional
blackbody at the Hawking temperature.Comment: 5 pages, 1 figure; v2: typo corrected, reference added; v3: comment
added, minor editorial changes to agree with published versio
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
Virtual Black Holes
One would expect spacetime to have a foam-like structure on the Planck scale
with a very high topology. If spacetime is simply connected (which is assumed
in this paper), the non-trivial homology occurs in dimension two, and spacetime
can be regarded as being essentially the topological sum of and
bubbles. Comparison with the instantons for pair creation of black holes
shows that the bubbles can be interpreted as closed loops of
virtual black holes. It is shown that scattering in such topological
fluctuations leads to loss of quantum coherence, or in other words, to a
superscattering matrix that does not factorise into an matrix and its
adjoint. This loss of quantum coherence is very small at low energies for
everything except scalar fields, leading to the prediction that we may never
observe the Higgs particle. Another possible observational consequence may be
that the angle of QCD is zero without having to invoke the
problematical existence of a light axion. The picture of virtual black holes
given here also suggests that macroscopic black holes will evaporate down to
the Planck size and then disappear in the sea of virtual black holes.Comment: 24p, LaTeX, 3 postscript figures included with epsf sent in a
seperate uuencoded fil
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
Thermodynamics of Reissner-Nordstrom-anti-de Sitter black holes in the grand canonical ensemble
The thermodynamical properties of the Reissner-Nordstr\"om-anti-de Sitter
black hole in the grand canonical ensemble are investigated using York's
formalism. The black hole is enclosed in a cavity with finite radius where the
temperature and electrostatic potential are fixed. The boundary conditions
allow us to compute the relevant thermodynamical quantities, e.g. thermal
energy, entropy and charge. The stability conditions imply that there are
thermodynamically stable black hole solutions, under certain conditions.
Instantons with negative heat capacity are also found.Comment: 15 pages, 9 figures, Revtex. Published version. Changes: figures
added to tex
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