7,352 research outputs found
New Local Duals in Eternal Inflation
Global-local duality is the equivalence of seemingly different regulators in
eternal inflation. For example, the light-cone time cutoff (a global measure,
which regulates time) makes the same predictions as the causal patch (a local
measure that cuts off space). We show that global-local duality is far more
general. It rests on a redundancy inherent in any global cutoff: at late times,
an attractor regime is reached, characterized by the unlimited exponential
self-reproduction of a certain fundamental region of spacetime. An equivalent
local cutoff can be obtained by restricting to this fundamental region.
We derive local duals to several global cutoffs of interest. The New Scale
Factor Cutoff is dual to the Short Fat Geodesic, a geodesic of fixed
infinitesimal proper width. Vilenkin's CAH Cutoff is equivalent to the
Hubbletube, whose width is proportional to the local Hubble volume. The famous
youngness problem of the Proper Time Cutoff can be readily understood by
considering its local dual, the Incredible Shrinking Geodesic.Comment: 30 pages, 3 figure
Light-sheets and Bekenstein's bound
From the covariant bound on the entropy of partial light-sheets, we derive a
version of Bekenstein's bound: S/M \leq pi x/hbar, where S, M, and x are the
entropy, total mass, and width of any isolated, weakly gravitating system.
Because x can be measured along any spatial direction, the bound becomes
unexpectedly tight in thin systems. Our result completes the identification of
older entropy bounds as special cases of the covariant bound. Thus,
light-sheets exhibit a connection between information and geometry far more
general, but in no respect weaker, than that initially revealed by black hole
thermodynamics.Comment: 5 pages, 1 figure; v2: published version, improved discussion of weak
gravity condition, final paragraph adde
On the Lagrangian structure of 3D consistent systems of asymmetric quad-equations
Recently, the first-named author gave a classification of 3D consistent
6-tuples of quad-equations with the tetrahedron property; several novel
asymmetric 6-tuples have been found. Due to 3D consistency, these 6-tuples can
be extended to discrete integrable systems on Z^m. We establish Lagrangian
structures and flip-invariance of the action functional for the class of
discrete integrable systems involving equations for which some of the
biquadratics are non-degenerate and some are degenerate. This class covers,
among others, some of the above mentioned novel systems.Comment: 21 pp, pdfLaTe
Research and applications: Artificial intelligence
The program is reported for developing techniques in artificial intelligence and their application to the control of mobile automatons for carrying out tasks autonomously. Visual scene analysis, short-term problem solving, and long-term problem solving are discussed along with the PDP-15 simulator, LISP-FORTRAN-MACRO interface, resolution strategies, and cost effectiveness
(Anti-)Evaporation of Schwarzschild-de Sitter Black Holes
We study the quantum evolution of black holes immersed in a de Sitter
background space. For black holes whose size is comparable to that of the
cosmological horizon, this process differs significantly from the evaporation
of asymptotically flat black holes. Our model includes the one-loop effective
action in the s-wave and large N approximation. Black holes of the maximal mass
are in equilibrium. Unexpectedly, we find that nearly maximal quantum
Schwarzschild-de Sitter black holes anti-evaporate. However, there is a
different perturbative mode that leads to evaporation. We show that this mode
will always be excited when a pair of cosmological holes nucleates.Comment: 16 pages, LaTeX2e; submitted to Phys. Rev.
Radiation osteitis of the clavicle
The bone alterations in the region of the clavicle (3 cases) are similar to those we have observed and described elsewhere in the skeleton i.e., the mandible, maxillary and ethmoid bones. Rarefaction is the result of three different types of bone destruction: osteoclasia, a kind of osteocytic osteolysis only observed after irradiation and obviously related with infection, and a pure demineralization of the osseous tissue by contact with pus. Reconstruction processes, although unable to prevent spontaneous fracture, are also present and correspond to islets of chondroid tissue surrounded by lamellar bone. However, these recently deposited calcified tissues are already necrotic since most of their lacunae are empty.Les modifications osseuses dans la région de la clavicule (3 observations) sont semblables à celles observées ailleurs dans le squelette, par exemple la mandibule, le maxillaire et l’os ethmoïde. La raréfaction osseuse est le résultat de trois types différents de destruction: l’ostéoclasie, une espèce d’ostéolyse ostéocytaire observée après irradiation, en rapport certain avec une infection et une déminéralisation pure du tissu osseux en contact avec du pus. Les phénomènes de reconstruction, bien qu’incapables d’éviter une fracture spontanée, sont également présents et ils correspondent à des îlots de tissu chondroïde au sein de travées d’os lamellaire. Cependant ces tissus calcifiés récemment déposés sont déjà nécrosés puisque les ostéoplastes sont vides
Non-Sequential Double Ionization is a Completely Classical Photoelectric Effect
We introduce a unified and simplified theory of atomic double ionization. Our
results show that at high laser intensities ( watts/cm)
purely classical correlation is strong enough to account for all of the main
features observed in experiments to date
The Holographic Principle for General Backgrounds
We aim to establish the holographic principle as a universal law, rather than
a property only of static systems and special space-times. Our covariant
formalism yields an upper bound on entropy which applies to both open and
closed surfaces, independently of shape or location. It reduces to the
Bekenstein bound whenever the latter is expected to hold, but complements it
with novel bounds when gravity dominates. In particular, it remains valid in
closed FRW cosmologies and in the interior of black holes. We give an explicit
construction for obtaining holographic screens in arbitrary space-times (which
need not have a boundary). This may aid the search for non-perturbative
definitions of quantum gravity in space-times other than AdS.Comment: 15 pages, 4 figures. Based on a talk given at Strings '99. Includes a
reply to recent criticism. For more details, examples, and references, see
hep-th/9905177 and hep-th/990602
Continuations of the nonlinear Schr\"odinger equation beyond the singularity
We present four continuations of the critical nonlinear \schro equation (NLS)
beyond the singularity: 1) a sub-threshold power continuation, 2) a
shrinking-hole continuation for ring-type solutions, 3) a vanishing
nonlinear-damping continuation, and 4) a complex Ginzburg-Landau (CGL)
continuation. Using asymptotic analysis, we explicitly calculate the limiting
solutions beyond the singularity. These calculations show that for generic
initial data that leads to a loglog collapse, the sub-threshold power limit is
a Bourgain-Wang solution, both before and after the singularity, and the
vanishing nonlinear-damping and CGL limits are a loglog solution before the
singularity, and have an infinite-velocity{\rev{expanding core}} after the
singularity. Our results suggest that all NLS continuations share the universal
feature that after the singularity time , the phase of the singular core
is only determined up to multiplication by . As a result,
interactions between post-collapse beams (filaments) become chaotic. We also
show that when the continuation model leads to a point singularity and
preserves the NLS invariance under the transformation and
, the singular core of the weak solution is symmetric
with respect to . Therefore, the sub-threshold power and
the{\rev{shrinking}}-hole continuations are symmetric with respect to ,
but continuations which are based on perturbations of the NLS equation are
generically asymmetric
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