353 research outputs found
De Sitter Space and Spatial Topology
Morrow-Jones and Witt have shown that generic spatial topologies admit
initial data that evolve to locally de Sitter spacetimes under Einstein's
equations. We simplify their arguments, make them a little more general, and
solve for the global time evolution of the wormhole initial data considered by
them. Finally we give explicit examples of locally de Sitter domains of
development whose universal covers cannot be embedded in de Sitter space.Comment: 21 pages, 7 figure
Results from Commissioning of the Energy Extraction Facilities of the LHC Machine
The risk of damage to the superconducting magnets, bus bars and current leads of the LHC machine in case of a resistive transition (quench) is being minimized by adequate protection. The protection is based on early quench detection, bypassing the quenching magnets by cold diodes, energy density dilution in the quenching magnets using heaters and, eventually, energy extraction. For two hundred and twenty-six LHC circuits (600 A and 13 kA) extraction of the stored magnetic energy to external dump resistors was required. All these systems are now installed in the machine and the final hardware commissioning has been undertaken. After a short description of the topology and definitive features, layouts and parameters of these systems the paper will focus on the results from their successful commissioning and an analysis of the system performance
Chern-Simons Quantization of (2+1)-Anti-De Sitter Gravity on a Torus
Chern-Simons formulation of 2+1 dimensional Einstein gravity with a negative
cosmological constant is investigated when the spacetime has the topology . The physical phase space is shown to be a direct product of two
sub-phase spaces each of which is a non-Hausdorff manifold plus a set with
nonzero codimensions. Spacetime geometrical interpretation of each point in the
phase space is also given and we explain the 1 to 2 correspondence with the ADM
formalism from the geometrical viewpoint. In quantizing this theory, we
construct a "modified phase space" which is a cotangnt bundle on a torus. We
also provide a modular invariant inner product and investigate the relation to
the quantum theory which is directly related to the spinor representation of
the ADM formalism. (This paper is the revised version of a previous
paper(hep-th/9312151). The wrong discussion on the topology of the phase space
is corrected.)Comment: latex 28 page
Geometry and observables in (2+1)-gravity
We review the geometrical properties of vacuum spacetimes in (2+1)-gravity
with vanishing cosmological constant. We explain how these spacetimes are
characterised as quotients of their universal cover by holonomies. We explain
how this description can be used to clarify the geometrical interpretation of
the fundamental physical variables of the theory, holonomies and Wilson loops.
In particular, we discuss the role of Wilson loop observables as the generators
of the two fundamental transformations that change the geometry of
(2+1)-spacetimes, grafting and earthquake. We explain how these variables can
be determined from realistic measurements by an observer in the spacetime.Comment: Talk given at 2nd School and Workshop on Quantum Gravity and Quantum
Geometry (Corfu, September 13-20 2009); 10 pages, 13 eps figure
The Torus Universe in the Polygon Approach to 2+1-Dimensional Gravity
In this paper we describe the matter-free toroidal spacetime in 't Hooft's
polygon approach to 2+1-dimensional gravity (i.e. we consider the case without
any particles present). Contrary to earlier results in the literature we find
that it is not possible to describe the torus by just one polygon but we need
at least two polygons. We also show that the constraint algebra of the polygons
closes.Comment: 18 pages Latex, 13 eps-figure
Collisions of particles in locally AdS spacetimes II Moduli of globally hyperbolic spaces
We investigate 3-dimensional globally hyperbolic AdS manifolds containing
"particles", i.e., cone singularities of angles less than along a
time-like graph . To each such space we associate a graph and a finite
family of pairs of hyperbolic surfaces with cone singularities. We show that
this data is sufficient to recover the space locally (i.e., in the neighborhood
of a fixed metric). This is a partial extension of a result of Mess for
non-singular globally hyperbolic AdS manifolds.Comment: 29 pages, 3 figures. v2: 41 pages, improved exposition. To appear,
Comm. Math. Phys. arXiv admin note: text overlap with arXiv:0905.182
3-manifolds which are spacelike slices of flat spacetimes
We continue work initiated in a 1990 preprint of Mess giving a geometric
parameterization of the moduli space of classical solutions to Einstein's
equations in 2+1 dimensions with cosmological constant 0 or -1 (the case +1 has
been worked out in the interim by the present author). In this paper we make a
first step toward the 3+1-dimensional case by determining exactly which closed
3-manifolds M^3 arise as spacelike slices of flat spacetimes, and by finding
all possible holonomy homomorphisms pi_1(M^3) to ISO(3,1).Comment: 10 page
Uniqueness of de Sitter space
All inextendible null geodesics in four dimensional de Sitter space dS^4 are
complete and globally achronal. This achronality is related to the fact that
all observer horizons in dS^4 are eternal, i.e. extend from future infinity
scri^+ all the way back to past infinity scri^-. We show that the property of
having a null line (inextendible achronal null geodesic) that extends from
scri^- to scri^+ characterizes dS^4 among all globally hyperbolic and
asymptotically de Sitter spacetimes satisfying the vacuum Einstein equations
with positive cosmological constant. This result is then further extended to
allow for a class of matter models that includes perfect fluids.Comment: 22 pages, 2 figure
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