2,403 research outputs found
Field Theory as Free Fall
It is shown that the classical field equations pertaining to gravity coupled
to other bosonic fields are equivalent to a single geodesic equation,
describing the free fall of a point particle in superspace. Some implications
for quantum gravity are discussed.Comment: 18 pages, plain late
Quantization in black hole backgrounds
Quantum field theory in a semiclassical background can be derived as an
approximation to quantum gravity from a weak-coupling expansion in the inverse
Planck mass. Such an expansion is studied for evolution on "nice-slices" in the
spacetime describing a black hole of mass M. Arguments for a breakdown of this
expansion are presented, due to significant gravitational coupling between
fluctuations, which is consistent with the statement that existing calculations
of information loss in black holes are not reliable. For a given fluctuation,
the coupling to subsequent fluctuations becomes of order unity by a time of
order M^3. Lack of a systematic derivation of the weakly-coupled/semiclassical
approximation would indicate a role for the non-perturbative dynamics of
gravity, and possibly for the proposal that such dynamics has an essentially
non-local quality.Comment: 28 pages, 4 figures, harvmac. v2: added refs, minor clarification
High energy QCD scattering, the shape of gravity on an IR brane, and the Froissart bound
High-energy scattering in non-conformal gauge theories is investigated using
the AdS/CFT dual string/gravity theory. It is argued that strong-gravity
processes, such as black hole formation, play an important role in the dual
dynamics. Further information about this dynamics is found by performing a
linearized analysis of gravity for a mass near an infrared brane; this gives
the far field approximation to black hole or other strong-gravity effects, and
in particular allows us to estimate their shape. From this shape, one can infer
a total scattering cross-section that grows with center of mass energy as ln^2
E, saturating the Froissart bound.Comment: 27 pages, 1 fig, harvmac. v2: references added, typos corrected v3:
typo correcte
Comments on information loss and remnants
The information loss and remnant proposals for resolving the black hole
information paradox are reconsidered. It is argued that in typical cases
information loss implies energy loss, and thus can be thought of in terms of
coupling to a spectrum of ``fictitious'' remnants. This suggests proposals for
information loss that do not imply planckian energy fluctuations in the low
energy world. However, if consistency of gravity prevents energy
non-conservation, these remnants must then be considered to be real. In either
case, the catastrophe corresponding to infinite pair production remains a
potential problem. Using Reissner-Nordstrom black holes as a paradigm for a
theory of remnants, it is argued that couplings in such a theory may give
finite production despite an infinite spectrum. Evidence for this is found in
analyzing the instanton for Schwinger production; fluctuations from the
infinite number of states lead to a divergent stress tensor, spoiling the
instanton calculation. Therefore naive arguements for infinite production fail.Comment: 30 pages (harvmac l mode) UCSBTH-93-35 (minor reference and typo
corrections
Linking the trans-Planckian and the information loss problems in black hole physics
The trans-Planckian and information loss problems are usually discussed in
the literature as separate issues concerning the nature of Hawking radiation.
Here we instead argue that they are intimately linked, and can be understood as
"two sides of the same coin" once it is accepted that general relativity is an
effective field theory.Comment: 10 pages, 2 figures. Replaced with the version to be published in
General Relativity and Gravitatio
Numerical Analysis of Black Hole Evaporation
Black hole formation/evaporation in two-dimensional dilaton gravity can be
described, in the limit where the number of matter fields becomes large, by
a set of second-order partial differential equations. In this paper we solve
these equations numerically. It is shown that, contrary to some previous
suggestions, black holes evaporate completely a finite time after formation. A
boundary condition is required to evolve the system beyond the naked
singularity at the evaporation endpoint. It is argued that this may be
naturally chosen so as to restore the system to the vacuum. The analysis also
applies to the low-energy scattering of -wave fermions by four-dimensional
extremal, magnetic, dilatonic black holes.Comment: 10 pages, 9 figures in separate uuencoded fil
A qualitative study of 2Create: A mental health service user-led art group
Background: 2Create is a mental health service user-led art group in the UK established by graduates of Open Arts, a community arts and mental health project. The study aimed to explore group members’ experiences over its first year.
Methods: Semi-structured interviews were conducted with five current and one former member of 2Create.
Results: Key themes related to organisation (evolving; flexibility; finance; leadership challenges), the studio environment, personal gains (social inclusion; self-esteem; well-being) and future plans (increasing membership; exhibitions; funding applications; social events).
Conclusion: The gains reported indicate that 2Create is beneficial to its members. Although a number of challenges were identified, all participants identified personal and group-wide gains and emphasised that challenges are to be expected when setting up a new group. The key implication for independent mental health user-led arts groups is that support is needed in the early stages and that independence can then be achieved with time
Information Loss and Anomalous Scattering
The approach of 't Hooft to the puzzles of black hole evaporation can be
applied to a simpler system with analogous features. The system is
dimensional electrodynamics in a linear dilaton background. Analogues of black
holes, Hawking radiation and evaporation exist in this system. In perturbation
theory there appears to be an information paradox but this gets resolved in the
full quantum theory and there exists an exact -matrix, which is fully
unitary and information conserving. 't Hooft's method gives the leading terms
in a systematic approximation to the exact result.Comment: 18 pages, 3 figures (postscript files available soon on request),
(earlier version got corrupted by mail system
The information paradox and the locality bound
Hawking's argument for information loss in black hole evaporation rests on
the assumption of independent Hilbert spaces for the interior and exterior of a
black hole. We argue that such independence cannot be established without
incorporating strong gravitational effects that undermine locality and
invalidate the use of quantum field theory in a semiclassical background
geometry. These considerations should also play a role in a deeper
understanding of horizon complementarity.Comment: 21 pages, harvmac; v2-3. minor corrections, references adde
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