Technol Rep Tohoku Univ: GENERATION OF ANTI-GRAVITY ...

RS Electrogravitic References
and Godel universes as well as the general
stationary, cylindrical, vacuum spacetimes.
Paper: gr-qc/9310030
From: khatsymovsky Date: Thu, 21 Oct 93
16:39:25 +0100
Can wormholes exist? V.Khatsymovsky, 10
pages, Plain LaTeX, preprint UUITP-
20/1993
Renormalized vacuum expectation values of
electromagnetic stress-energy tensor are
calculated in the background sphericallysymmetrical
metric of the wormhole's
topology. Covariant geodesic point separation
method of regularization is used. Violation of
the weak energy condition at the throat of
wormhole takes place for geometry sufficiently
close to that of infinitely long wormhole of
constant radius irrespectively of the detailed
form of metric. This is an argument in favour
of possibility of existence of selfconsistent
wormhole in empty space maintained by
vacuum field fluctuations in the wormhole's
background.
Paper: hep-th/9402046
From: LANDI@SUHEP.PHY.SYR.EDU
Date: Tue, 08 Feb 1994 15:09:39 -0500 (EST)
GRAVITY AND ELECTROMAGNETISM
IN NONCOMMUTATIVE GEOMETRY,
Giovanni Landi, Nguyen Ai Viet, Kameshwar
C.Wali, 1 + 11 pages, Report # SU-4240-566,
We present a unified description of gravity and
electromagnetism in the framework of a Z2
noncommutative differential calculus. It can be
considered as a ``discrete version" of Kaluza-
Klein theory, where the fifth continuous
dimension is replaced by two discrete points.
We derive an action which coincides with the
dimensionally reduced one of the ordinary
Kaluza-Klein theory.
Paper: gr-qc/9404016
From: David Garfinkle Date: Sun, 10 Apr
1994 17:44:50 -0400
Generating new magnetic universe solutions
from old. By David Garfinkle and M.A.
Melvin. 17 pages
In this paper we apply the techniques which
have been developed over the last few decades
for generating nontrivially new solutions of the
Einstein-Maxwell equations from seed
solutions for simple spacetimes. The simple
seed spacetime which we choose is the
"magnetic universe" to which we apply the
Ehlers transformation. Three interesting nonsingular
metrics are generated. Two of these
may be described as "rotating magnetic
universes" and the third as an "evolving
magnetic universe." Each is causally complete
- in that all timelike and lightlike geodesics do
not end in a finite time or affine parameter. We
also give the electromagnetic field in each
case. For the two rotating stationary cases we
give the projection with respect to a stationary
observer of the electromagnetic field into
electric and magnetic components.
Paper: gr-qc/9404065 (Phys. Rev. D50 (1994)
6190) From: carroll@marie.mit.edu (Sean
Carroll) Date: Sun, 1 May 1994 16:35:00 -
0400
Energy-Momentum Restrictions on the
Creation of Gott Time Machines, by Sean M.
Carroll, Edward Farhi, Alan H. Guth, and Ken
D. Olum. Plain TeX, 41 pages incl. 9 figures.
MIT-CTP #2252.
The discovery by Gott of a remarkably simple
spacetime with closed timelike curves (CTC's)
provides a tool for investigating how the
creation of time machines is prevented in
classical general relativity. The Gott spacetime
contains two infinitely long, parallel cosmic
strings, which can equivalently be viewed as
point masses in (2+1)-dimensional gravity. We
examine the possibility of building such a time
machine in an open universe. Specifically, we
consider initial data specified on an edgeless,
noncompact, spacelike hypersurface, for which
the total momentum is timelike (i.e., not the
momentum of a Gott spacetime). In contrast to
the case of a closed universe (in which Gott
pairs, although not CTC's, can be produced
from the decay of stationary particles), we find
that there is never enough energy for a Gottlike
time machine to evolve from the specified
data; it is impossible to accelerate two particles
to sufficiently high velocity. Thus, the no-CTC
theorems of Tipler and Hawking are enforced
in an open (2+1)-dimensional universe by a
mechanism different from that which operates
in a closed universe. In proving our result, we
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