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 $N$ 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 $S$-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 $1+1$ 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 $S$-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