1,602 research outputs found
On Dijkgraaf-Witten Type Invariants
We explicitly construct a series of lattice models based upon the gauge group
which have the property of subdivision invariance, when the coupling
parameter is quantized and the field configurations are restricted to satisfy a
type of mod- flatness condition. The simplest model of this type yields the
Dijkgraaf-Witten invariant of a -manifold and is based upon a single link,
or -simplex, field. Depending upon the manifold's dimension, other models
may have more than one species of field variable, and these may be based on
higher dimensional simplices.Comment: 18 page
Birminghamâs Eastside story: making steps towards sustainability?
Sustainability has come to play a dominant discursive role in the UK planning system, particularly relating to urban regeneration. The purpose of this paper is to evaluate the role that sustainability plays in a major regeneration
programme, known as Eastside, currently underway in Birmingham, the UK. That this ÂŁ6 billion redevelopment is now widely talked about by such key players as Birmingham City Council and the Regional Development Agency, Advantage West Midlands, as having a central sustainability agenda points to the growing importance of the ideal of sustainability in planning and regeneration agendas. In this paper, we investigate in detail how and why sustainability has become part of the planning discourse for Eastside and critically evaluate what impact, if any, this is having on public policy decision-making
A New Action Principle for Witten's Topological Field Theory
In this letter a new gauge invariant, metric independent action is introduced
from which Witten's Topological Quantum Field Theory may be obtained after
gauge fixing using standard BRST techniques. In our model the BRST algebra of
transformations, under which the effective action is invariant, close off-shell
in distintion with what occurs in the one proposed by Labastida and Pernici.
Our approach provides the geometrical principle for the quantum theory. We also
compare our results with an alternative formulation presented by Baulieu and
Singer.Comment: 8 pages, SB/F-94-22
Robinson-Trautman spacetimes in higher dimensions
As an extension of the Robinson-Trautman solutions of D=4 general relativity,
we investigate higher dimensional spacetimes which admit a hypersurface
orthogonal, non-shearing and expanding geodesic null congruence. Einstein's
field equations with an arbitrary cosmological constant and possibly an aligned
pure radiation are fully integrated, so that the complete family is presented
in closed explicit form. As a distinctive feature of higher dimensions, the
transverse spatial part of the general line element must be a Riemannian
Einstein space, but it is otherwise arbitrary. On the other hand, the remaining
part of the metric is - perhaps surprisingly - not so rich as in the standard
D=4 case, and the corresponding Weyl tensor is necessarily of algebraic type D.
While the general family contains (generalized) static
Schwarzschild-Kottler-Tangherlini black holes and extensions of the Vaidya
metric, there is no analogue of important solutions such as the C-metric.Comment: 11 page
An Exact Black Hole Entropy Bound
We show that a Rademacher expansion can be used to establish an exact bound
for the entropy of black holes within a conformal field theory framework. This
convergent expansion includes all subleading corrections to the
Bekenstein-Hawking term.Comment: 6 pages, Latex, v2 minor re-wording, additional reference, to appear
in Phyical Review D (title changed in journal
Gauge symmetry breaking on orbifolds
We discuss a new method for gauge symmetry breaking in theories with one
extra dimension compactified on the orbifold S^1/Z_2. If we assume that fields
and their derivatives can jump at the orbifold fixed points, we can implement a
generalized Scherk-Schwarz mechanism that breaks the gauge symmetry. We show
that our model with discontinuous fields is equivalent to another with
continuous but non periodic fields; in our scheme localized lagrangian terms
for bulk fields appear.Comment: 6 pages, 2 figures. Talk given at the XXXVIIth Rencontres de Moriond,
"Electroweak interactions and unified theories", Les Arcs, France, 9-16 Mar
2002. Minor changes, one reference adde
Brane-world generalizations of the Einstein static universe
A static Friedmann brane in a 5-dimensional bulk (Randall-Sundrum type
scenario) can have a very different relation between the density, pressure,
curvature and cosmological constant than in the case of the general
relativistic Einstein static universe. In particular, static Friedmann branes
with zero cosmological constant and 3-curvature, but satisfying rho>0 and
rho+3p>0, are possible. Furthermore, we find static Friedmann branes in a bulk
that satisfies the Einstein equations but is not Schwarzschild-anti de Sitter
or its specializations. In the models with negative bulk cosmological constant,
a positive brane tension leads to negative density and 3-curvature.Comment: additional interpretation of new solutions; accepted by
Class.Quant.Gra
Universal canonical entropy for gravitating systems
The thermodynamics of general relativistic systems with boundary, obeying a
Hamiltonian constraint in the bulk, is argued to be determined solely by the
boundary quantum dynamics, and hence by the area spectrum. Assuming, for large
area of the boundary, (a) an area spectrum as determined by Non-perturbative
Canonical Quantum General Relativity (NCQGR), (b) an energy spectrum that bears
a power law relation to the area spectrum, (c) an area law for the leading
order microcanonicai entropy, leading thermal fluctuation corrections to the
canonical entropy are shown to be logarithmic in area with a universal
coefficient. Since the microcanonical entropy also has univeral logarithmic
corrections to the area law (from quantum spacetime fluctuations, as found
earlier) the canonical entropy then has a universal form including logarithmic
corrections to the area law. This form is shown to be independent of the index
appearing in assumption (b). The index, however, is crucial in ascertaining the
domain of validity of our approach based on thermal equilibrium.Comment: 6 pages revtex, one eps figure; based on talk delivered at the
International Conference on Gravitation and Cosmology held at Kochi, India
during 5-9 January, 200
Area Spectrum of Kerr and extremal Kerr Black Holes from Quasinormal Modes
Motivated by the recent interest in quantization of black hole area spectrum,
we consider the area spectrum of Kerr and extremal Kerr black holes. Based on
the proposal by Bekenstein and others that the black hole area spectrum is
discrete and equally spaced, we implement Kunstatter's method to derive the
area spectrum for the Kerr and extremal Kerr black holes. The real part of the
quasinormal frequencies of Kerr black hole used for this computation is of the
form where is the angular velocity of the black hole
horizon. The resulting spectrum is discrete but not as expected uniformly
spaced. Thus, we infer that the function describing the real part of
quasinormal frequencies of Kerr black hole is not the correct one. This
conclusion is in agreement with the numerical results for the highly damped
quasinormal modes of Kerr black hole recently presented by Berti, Cardoso and
Yoshida. On the contrary, extremal Kerr black hole is shown to have a discrete
area spectrum which in addition is evenly spaced. The area spacing derived in
our analysis for the extremal Kerr black hole area spectrum is not proportional
to . Therefore, it does not give support to Hod's statement that the
area spectrum should be valid for a generic
Kerr-Newman black hole.Comment: 10 pages, no figure, LaTeX; v2: 12 pages, clarifying comments and an
Appendix are added, version to appear in Mod. Phys. Lett.
Quasinormal Modes of Extremal BTZ Black Hole
Motivated by several pieces of evidence, in order to show that extreme black
holes cannot be obtained as limits of non-extremal black holes, in this article
we calculate explicitly quasinormal modes for Ba\~{n}ados, Teitelboim and
Zanelli (BTZ) extremal black hole and we showed that the imaginary part of the
frequency is zero. We obtain exact result for the scalar an fermionic
perturbations. We also showed that the frequency is bounded from below for the
existence of the normal modes (non-dissipative modes).Comment: 6 pp. Accepted Classical and Quantum Gravity. Typos corrected and
some references was added. Final Versio
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