773 research outputs found

### General existence proof for rest frame systems in asymptotically flat space-time

We report a new result on the nice section construction used in the
definition of rest frame systems in general relativity. This construction is
needed in the study of non trivial gravitational radiating systems. We prove
existence, regularity and non-self-crossing property of solutions of the nice
section equation for general asymptotically flat space times. This proves a
conjecture enunciated in a previous work.Comment: 14 pages, no figures, LaTeX 2

### Asymptotic flatness at null infinity in arbitrary dimensions

We define the asymptotic flatness and discuss asymptotic symmetry at null
infinity in arbitrary dimensions using the Bondi coordinates. To define the
asymptotic flatness, we solve the Einstein equations and look at the asymptotic
behavior of gravitational fields. Then we show the asymptotic symmetry and the
Bondi mass loss law with the well-defined definition.Comment: 12 pages, published version in PR

### Quasistationary binary inspiral. I. Einstein equations for the two Killing vector spacetime

The geometry of two infinitely long lines of mass moving in a fixed circular
orbit is considered as a toy model for the inspiral of a binary system of
compact objects due to gravitational radiation. The two Killing fields in the
toy model are used, according to a formalism introduced by Geroch, to describe
the geometry entirely in terms of a set of tensor fields on the two-manifold of
Killing vector orbits. Geroch's derivation of the Einstein equations in this
formalism is streamlined and generalized. The explicit Einstein equations for
the toy model spacetime are derived in terms of the degrees of freedom which
remain after a particular choice of gauge.Comment: 37 pages, REVTeX, one PostScript Figure included with epsfig; minor
formatting changes and copyright notice added for journal publicatio

### Quasi-Asimptotically Flat Spacetimes and Their ADM Mass

We define spacetimes that are asymptotically flat, except for a deficit solid
angle $\alpha$, and present a definition of their ``ADM'' mass, which is finite
for this class of spacetimes, and, in particular, coincides with the value of
the parameter $M$ of the global monopole spacetime studied by Vilenkin and
Barriola . Moreover, we show that the definition is coordinate independent, and
explain why it can, in some cases, be negative.Comment: Late

### The Topology of Branching Universes

The purpose of this paper is to survey the possible topologies of branching
space-times, and, in particular, to refute the popular notion in the literature
that a branching space-time requires a non-Hausdorff topology

### Formation of closed timelike curves in a composite vacuum/dust asymptotically-flat spacetime

We present a new asymptotically-flat time-machine model made solely of vacuum
and dust. The spacetime evolves from a regular spacelike initial hypersurface S
and subsequently develops closed timelike curves. The initial hypersurface S is
asymptotically flat and topologically trivial. The chronology violation occurs
in a compact manner; namely the first closed causal curves form at the boundary
of the future domain of dependence of a compact region in S (the core). This
central core is empty, and so is the external asymptotically flat region. The
intermediate region surrounding the core (the envelope) is made of dust with
positive energy density. This model trivially satisfies the weak, dominant, and
strong energy conditions. Furthermore it is governed by a well-defined system
of field equations which possesses a well-posed initial-value problem.Comment: 15 pages; accepted to Phys. Rev. D (no modifications

### The Physics Inside Topological Quantum Field Theories

We show that the equations of motion defined over a specific field space are
realizable as operator conditions in the physical sector of a generalized Floer
theory defined over that field space. The ghosts associated with such a
construction are found not to be dynamical. This construction is applied to
gravity on a four dimensional manifold, $M$; whereupon, we obtain Einstein's
equations via surgery, along $M$, in a five-dimensional topological quantum
field theory.Comment: LaTeX, 7 page

### Radiative observables for linearized gravity on asymptotically flat spacetimes and their boundary induced states

We discuss the quantization of linearized gravity on globally hyperbolic,
asymptotically flat, vacuum spacetimes and the construction of distinguished
states which are both of Hadamard form and invariant under the action of all
bulk isometries. The procedure, we follow, consists of looking for a
realization of the observables of the theory as a sub-algebra of an auxiliary,
non-dynamical algebra constructed on future null infinity $\Im^+$. The
applicability of this scheme is tantamount to proving that a solution of the
equations of motion for linearized gravity can be extended smoothly to $\Im^+$.
This has been claimed to be possible provided that a suitable gauge fixing
condition, first written by Geroch and Xanthopoulos, is imposed. We review its
definition critically showing that there exists a previously unnoticed
obstruction in its implementation leading us to introducing the concept of
radiative observables. These constitute an algebra for which a Hadamard state
induced from null infinity and invariant under the action of all spacetime
isometries exists and it is explicitly constructed.Comment: 31 pages, added reference

### Causally simple inextendible spacetimes are hole-free

It is shown that causally simple inextendible spacetimes are hole-free, thus
confirming the expectation that causal simplicity removes holes from spacetime.
This result is optimal in the sense that causal simplicity cannot be weakened
to causal continuity. Physically, it means that if there is some partial Cauchy
hypersurface which, for some reason, does not fully develop its influence, then
there is some discontinuity in the causal relation.Comment: Revtex4, 9 pages. v2: minor correction

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