Thin shells joining local cosmic string geometries
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Abstract:
In this article we present a theoretical construction of spacetimes with a thin shell that joins two different local cosmic string geometries. We study two types of global manifolds, one representing spacetimes with a thin shell surrounding a cosmic string or an empty region with Minkowski metric, and the other corresponding to wormholes which are not symmetric across the throat located at the shell. We analyze the stability of the static configurations under perturbations preserving the cylindrical symmetry. For both types of geometries we find that the static configurations can be stable for suitable values of the parameters.Keywords:
Cosmic string
Wormhole
The first part of this paper discusses a model for the theoretical construction of a simple traversable wormhole with zero density that depends on a preexisting black hole. By assuming the interconvertibilty of black holes and wormholes proposed by S.A. Hayward, it is shown that a toy model suggested by the first model may yield several possible transitions from the preexisting black hole to a wormhole. A final topic is the conversion to a wormhole by assuming a specific model for the exotic matter.
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We describe the analytical extension of certain static cylindrical multi--cosmic string metrics to wormhole spacetimes with only one region at spatial infinity, and investigate in detail the geometry of asymptotically Minkowskian wormhole spacetimes generated by one or two cosmic strings. We find that such wormholes tend to lengthen rather than shorten space travel. Possible signatures of these wormholes are briefly discussed.
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We investigate the contribution made by small loops from a cosmic string network as seeds for large-scale structure formation. We show that cosmic string loops are highly correlated with the long-string network on large scales and therefore contribute significantly to the power spectrum of density perturbations if the average loop lifetime is comparable to or above one Hubble time. This effect further improves the large-scale bias problem previously identified in earlier studies of cosmic string models. @S0556-2821~99!01614-8# Quantitative predictions for the large-scale structure induced by cosmic strings have taken some time to crystallize as the understanding of cosmic string physics has improved @1#. In particular, the role of small loops produced by the string network has evolved from a potential one-to-one correspondence between loops and cosmological objects @2# through to a completely subsidiary role relative to the wakes swept out by long strings @3#. This dethronement of loops was a result of numerical studies which showed that the average loop size l ¯ 5at was much smaller than the horizon,
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