1,500 research outputs found
Geometric Analysis of Particular Compactly Constructed Time Machine Spacetimes
We formulate the concept of time machine structure for spacetimes exhibiting
a compactely constructed region with closed timelike curves. After reviewing
essential properties of the pseudo Schwarzschild spacetime introduced by A.
Ori, we present an analysis of its geodesics analogous to the one conducted in
the case of the Schwarzschild spacetime. We conclude that the pseudo
Schwarzschild spacetime is geodesically incomplete and not extendible to a
complete spacetime. We then introduce a rotating generalization of the pseudo
Schwarzschild metric, which we call the the pseudo Kerr spacetime. We establish
its time machine structure and analyze its global properties.Comment: 14 pages, 3 figure
A Note On Zeroes Of Superpotentials In F-Theory
We discuss the dependence of superpotential terms in 4D F-theory on moduli
parameters. Two cases are studied: the dependence on world-filling 3-brane
positions and the dependence on 2-form VEVs. In the first case there is a zero
when the 3-brane hits the divisor responsible for the superpotential. In the
second case, which has been extensively discussed by Witten in 3D M-theory,
there is a zero for special values of 2-form VEVs when the M-theory divisor
contains non-trivial 3-cycles. We give an alternative derivation of this fact
for the special case of F-theory.Comment: 12pp Te
Dipoles, Twists and Noncommutative Gauge Theory
T-duality of gauge theories on a noncommutative can be extended to
include fields with twisted boundary conditions. The resulting T-dual theories
contain novel nonlocal fields. These fields represent dipoles of constant
magnitude. Several unique properties of field theories on noncommutative spaces
have simpler counterparts in the dipole-theories.Comment: 20pp LaTeX, amsfonts and amssymb, JHEP format and ref adde
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