958 research outputs found
Symmetry Breaking Using Value Precedence
We present a comprehensive study of the use of value precedence constraints
to break value symmetry. We first give a simple encoding of value precedence
into ternary constraints that is both efficient and effective at breaking
symmetry. We then extend value precedence to deal with a number of
generalizations like wreath value and partial interchangeability. We also show
that value precedence is closely related to lexicographical ordering. Finally,
we consider the interaction between value precedence and symmetry breaking
constraints for variable symmetries.Comment: 17th European Conference on Artificial Intelligenc
Conservation Laws and 2D Black Holes in Dilaton Gravity
A very general class of Lagrangians which couple scalar fields to gravitation
and matter in two spacetime dimensions is investigated. It is shown that a
vector field exists along whose flow lines the stress-energy tensor is
conserved, regardless of whether or not the equations of motion are satisfied
or if any Killing vectors exist. Conditions necessary for the existence of
Killing vectors are derived. A new set of 2D black hole solutions is obtained
for one particular member within this class of Lagrangians. One such solution
bears an interesting resemblance to the 2D string-theoretic black hole, yet
contains markedly different thermodynamic properties.Comment: 11 pgs. WATPHYS-TH92/0
Super Black Hole from Cosmological Supergravity with a Massive Superparticle
We describe in superspace a classical theory of two dimensional
cosmological dilaton supergravity coupled to a massive superparticle. We give
an exact non-trivial superspace solution for the compensator superfield that
describes the supergravity, and then use this solution to construct a model of
a two-dimensional supersymmetric black hole.Comment: 7 pages, Late
Liouville Black Holes
The dynamics of Liouville fields coupled to gravity are investigated by
applying the principle of general covariance to the Liouville action in the
context of a particular form of two-dimensional dilaton gravity. The resultant
field equations form a closed system for the Liouville/gravity interaction. A
large class of asymptotically flat solutions to the field equations is
obtained, many of which can be interpreted as black hole solutions. The
temperature of such black holes is proportional to their mass-parameters. An
exact solution to the back reaction problem is obtained to one-loop order, both
for conformally coupled matter fields and for the quantized metric/Liouville
system. Quantum effects are shown to map the space of classical solutions into
one another. A scenario for the end-point of black-hole radiation is discussed.Comment: 32 pgs., WATPHYS-TH93/03 (Latex plus two postscript figures appended
Uniformly accelerating black holes in a de Sitter universe
A class of exact solutions of Einstein's equations is analysed which
describes uniformly accelerating charged black holes in an asymptotically de
Sitter universe. This is a generalisation of the C-metric which includes a
cosmological constant. The physical interpretation of the solutions is
facilitated by the introduction of a new coordinate system for de Sitter space
which is adapted to accelerating observers in this background. The solutions
considered reduce to this form of the de Sitter metric when the mass and charge
of the black holes vanish.Comment: 6 pages REVTeX, 3 figures, to appear in Phys. Rev. D. Figure 2
correcte
Bubbles Unbound: Bubbles of Nothing Without Kaluza-Klein
I present analytic time symmetric initial data for five dimensions describing
``bubbles of nothing'' which are asymptotically flat in the higher dimensional
sense, i.e. there is no Kaluza-Klein circle asymptotically. The mass and size
of these bubbles may be chosen arbitrarily and in particular the solutions
contain bubbles of any size which are arbitrarily light. This suggests the
solutions may be important phenomenologically and in particular I show that at
low energy there are bubbles which expand outwards, suggesting a new possible
instability in higher dimensions. Further, one may find bubbles of any size
where the only region of high curvature is confined to an arbitrarily small
volume.Comment: 27 pages, 2 figures, v2: minor changes, published versio
Self-completeness and spontaneous dimensional reduction
A viable quantum theory of gravity is one of the biggest challenges facing
physicists. We discuss the confluence of two highly expected features which
might be instrumental in the quest of a finite and renormalizable quantum
gravity -- spontaneous dimensional reduction and self-completeness. The former
suggests the spacetime background at the Planck scale may be effectively
two-dimensional, while the latter implies a condition of maximal compression of
matter by the formation of an event horizon for Planckian scattering. We
generalize such a result to an arbitrary number of dimensions, and show that
gravity in higher than four dimensions remains self-complete, but in lower
dimensions it is not. In such a way we established an "exclusive disjunction"
or "exclusive or" (XOR) between the occurrence of self-completeness and
dimensional reduction, with the goal of actually reducing the unknowns for the
scenario of the physics at the Planck scale. Potential phenomenological
implications of this result are considered by studying the case of a
two-dimensional dilaton gravity model resulting from dimensional reduction of
Einstein gravity.Comment: 12 pages, 3 figures; v3: final version in press on Eur. Phys. J. Plu
Harrison transformation and charged black objects in Kaluza-Klein theory
We generate charged black brane solutions in dimensions in a theory of
gravity coupled to a dilaton and an antisymmetric form, by using a
Harrison-type transformation. The seed vacuum solutions that we use correspond
to uplifted Kaluza-Klein black strings and black holes in -dimensions. A
generalization of the Marolf-Mann quasilocal formalism to the Kaluza-Klein
theory is also presented, the global charges of the black objects being
computed in this way. We argue that the thermodynamics of the charged solutions
can be derived from that of the vacuum configurations. Our results show that
all charged Kaluza-Klein solutions constructed by means of Harrison
transformations are thermodynamically unstable in a grand canonical ensemble.
The general formalism is applied to the case of nonuniform black strings and
caged black hole solutions in Einstein-Maxwell-dilaton gravity, whose
geometrical properties and thermodynamics are discussed. We argue that the
topology changing transition scenario, which was previously proposed in the
vacuum case, also holds in this case. Spinning generalizations of the charged
black strings are constructed in six dimensions in the slowly rotating limit.
We find that the gyromagnetic ratio of these solutions possesses a nontrivial
dependence on the nonuniformity parameter.Comment: 42 pages, 12 figure
The Nature and Location of Quantum Information
Quantum information is defined by applying the concepts of ordinary (Shannon)
information theory to a quantum sample space consisting of a single framework
or consistent family. A classical analogy for a spin-half particle and other
arguments show that the infinite amount of information needed to specify a
precise vector in its Hilbert space is not a measure of the information carried
by a quantum entity with a -dimensional Hilbert space; the latter is,
instead, bounded by log d bits (1 bit per qubit). The two bits of information
transmitted in dense coding are located not in one but in the correlation
between two qubits, consistent with this bound. A quantum channel can be
thought of as a "structure" or collection of frameworks, and the physical
location of the information in the individual frameworks can be used to
identify the location of the channel. Analysis of a quantum circuit used as a
model of teleportation shows that the location of the channel depends upon
which structure is employed; for ordinary teleportation it is not (contrary to
Deutsch and Hayden) present in the two bits resulting from the Bell-basis
measurement, but in correlations of these with a distant qubit. In neither
teleportation nor dense coding does information travel backwards in time, nor
is it transmitted by nonlocal (superluminal) influences. It is (tentatively)
proposed that all aspects of quantum information can in principle be understood
in terms of the (basically classical) behavior of information in a particular
framework, along with the framework dependence of this information.Comment: Latex 29 pages, uses PSTricks for figure
The Equivalence Principle and g-2 Experiments
We consider the possibility of using measurements of anomalous magnetic
moments of elementary particles as a possible test of the Einstein Equivalence
Principle (EEP). For the class non-metric theories of gravity described by the
\tmu formalism we find several novel mechanisms for breaking the EEP, and
discuss the possibilities of setting new empirical constraints on such effects.Comment: 4 pages, latex, epsf, 1 figur
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