15 research outputs found
Closed Geodesics on Godel-type Backgrounds
We consider radial oscillations of supertube probes in the Godel-type
background which is U-dual to the compactified pp-wave obtained from the
Penrose limit of the NS five-brane near horizon geometry. The supertube probe
computation can be carried over directly to a string probe calculation on the
U-dual background. The classical equations of motion are solved explicitly. In
general, the probe is not restricted to travel unidirectionally through any
global time coordinate. In particular, we find geodesics that close.Comment: latex, 15 pages, 1 figure. v3: reference added, clarifications added
and some discussions expande
An example of localized D-branes solution on PP-wave backgrounds
In this note we provide an explicit example of type IIB supersymmetric
D3-branes solution on a pp-wave like background, consisting in the product of
an eight-dimensional pp-wave times a two-dimensional flat space. An interesting
property of our solution is the fully localization of the D3-branes (i.e. the
solution depends on all the transverse coordinates). Then we show the
generalization to other Dp-branes and to the D1/D5 system.Comment: 14 pages, 1 table; v2. references adde
G\"{o}del black hole, closed timelike horizon, and the study of particle emissions
We show that a particle, with positive orbital angular momentum, following an
outgoing null/timelike geodesic, shall never reach the closed timelike horizon
(CTH) present in the -dimensional rotating G\"{o}del black hole
space-time. Therefore a large part of this space-time remains inaccessible to a
large class of geodesic observers, depending on the conserved quantities
associated with them. We discuss how this fact and the existence of the closed
timelike curves present in the asymptotic region make the quantum field
theoretic study of the Hawking radiation, where the asymptotic observer states
are a pre-requisite, unclear. However, the semiclassical approach provides an
alternative to verify the Smarr formula derived recently for the rotating
G\"{o}del black hole. We present a systematic analysis of particle emissions,
specifically for scalars, charged Dirac spinors and vectors, from this black
hole via the semiclassical complex path method.Comment: 13 pages; minor changes, references adde
Classical and Quantum Strings in compactified pp-waves and Godel type Universes
We consider Neveu-Schwarz pp-waves with spacetime supersymmetry. Upon
compactification of a spacelike direction, these backgrounds develop Closed
Null Curves (CNCs) and Closed Timelike Curves (CTCs), and are U-dual to
supersymmetric Godel type universes. We study classical and quantum strings in
this background, with emphasis on the strings winding around the compact
direction. We consider two types of strings: long strings stabilized by NS flux
and rotating strings which are stabilized against collapse by angular momentum.
Some of the latter strings wrap around CNCs and CTCs, and are thus a potential
source of pathology. We analyze the partition function, and in particular
discuss the effects of these string states. Although our results are not
conclusive, the partition function seems to be dramatically altered due to the
presence of CNCs and CTCs. We discuss some interpretations of our results,
including a possible sign of unitary violation.Comment: 42 pages, LaTeX, 2 figure
Unwrapping Closed Timelike Curves
Closed timelike curves (CTCs) appear in many solutions of the Einstein
equation, even with reasonable matter sources. These solutions appear to
violate causality and so are considered problematic. Since CTCs reflect the
global properties of a spacetime, one can attempt to change its topology,
without changing its geometry, in such a way that the former CTCs are no longer
closed in the new spacetime. This procedure is informally known as unwrapping.
However, changes in global identifications tend to lead to local effects, and
unwrapping is no exception, as it introduces a special kind of singularity,
called quasi-regular. This "unwrapping" singularity is similar to the string
singularities. We give two examples of unwrapping of essentially 2+1
dimensional spacetimes with CTCs, the Gott spacetime and the Godel universe. We
show that the unwrapped Gott spacetime, while singular, is at least devoid of
CTCs. In contrast, the unwrapped Godel spacetime still contains CTCs through
every point. A "multiple unwrapping" procedure is devised to remove the
remaining circular CTCs. We conclude that, based on the two spacetimes we
investigated, CTCs appearing in the solutions of the Einstein equation are not
simply a mathematical artifact of coordinate identifications, but are indeed a
necessary consequence of General Relativity, provided only that we demand these
solutions do not possess naked quasi-regular singularities.Comment: 29 pages, 9 figure
M-theory on a Time-dependent Plane-wave
We propose a matrix model on a homogeneous plane-wave background with 20
supersymmetries. This background is anti-Mach type and is equivalent to the
time-dependent background. We study supersymmetries in this theory and
calculate the superalgebra. The vacuum energy of the abelian part is also
calculated. In addition we find classical solutions such as graviton solution,
fuzzy sphere and hyperboloid.Comment: 19pages, no figures, LaTeX, JHEP3.cl
Supersymmetric Intersections of M-branes and pp-waves
We study supersymmetric intersections of M2 and M5 branes with different
pp-waves of M-theory. We consider first M-brane probes in the background of
pp-waves and determine under which conditions the embedding is supersymmetric.
We particularize our formalism to the case of pp-waves with 32, 24 and 20
supersymmetries. We also construct supergravity solutions for the brane-wave
system. Generically these solutions are delocalised along some directions
transverse to the brane and preserve the same number of supersymmetries as in
the brane probe approach.Comment: 41 pages, LaTeX; v2 references adde
Killing spectroscopy of closed timelike curves
We analyse the existence of closed timelike curves in spacetimes which
possess an isometry. In particular we check which discrete quotients of such
spaces lead to closed timelike curves. As a by-product of our analysis, we
prove that the notion of existence or non-existence of closed timelike curves
is a T-duality invariant notion, whenever the direction along which we apply
such transformations is everywhere spacelike. Our formalism is
straightforwardly applied to supersymmetric theories. We provide some new
examples in the context of D-branes and generalized pp-waves.Comment: 1+35 pages, no figures; v2, new references added. Final version to
appear in JHE
Twisted Backgrounds, PP-Waves and Nonlocal Field Theories
We study partially supersymmetric plane-wave like deformations of string
theories and M-theory on brane backgrounds. These deformations are dual to
nonlocal field theories. We calculate various expectation values of
configurations of closed as well as open Wilson loops and Wilson surfaces in
those theories. We also discuss the manifestation of the nonlocality structure
in the supergravity backgrounds. A plane-wave like deformation of little string
theory has also been studied.Comment: 46 pages, changed to JHEP forma
Quotients of AdS_{p+1} x S^q: causally well-behaved spaces and black holes
Starting from the recent classification of quotients of Freund--Rubin
backgrounds in string theory of the type AdS_{p+1} x S^q by one-parameter
subgroups of isometries, we investigate the physical interpretation of the
associated quotients by discrete cyclic subgroups. We establish which quotients
have well-behaved causal structures, and of those containing closed timelike
curves, which have interpretations as black holes. We explain the relation to
previous investigations of quotients of asymptotically flat spacetimes and
plane waves, of black holes in AdS and of Godel-type universes.Comment: 48 pages; v2: minor typos correcte