67 research outputs found
Can a wormhole supported by only small amounts of exotic matter really be traversable?
Recent studies have shown that (a) quantum effects may be sufficient to
support a wormhole throat and (b) the total amount of "exotic matter" can be
made arbitrarily small. Unfortunately, using only small amounts of exotic
matter may result in a wormhole that flares out too slowly to be traversable in
a reasonable length of time. Combined with the Ford-Roman constraints, the
wormhole may also come close to having an event horizon at the throat. This
paper examines a model that overcomes these difficulties, while satisfying the
usual traversability conditions. This model also confirms that the total amount
of exotic matter can indeed be made arbitrarily small.Comment: 8 pages, AMSTe
Dynamic wormholes, anti-trapped surfaces, and energy conditions
Adapting and extending a suggestion due to Page, we define a wormhole throat
to be a marginally anti-trapped surface, that is, a closed two-dimensional
spatial hypersurface such that one of the two future-directed null geodesic
congruences orthogonal to it is just beginning to diverge. Typically a dynamic
wormhole will possess two such throats, corresponding to the two orthogonal
null geodesic congruences, and these two throats will not coincide, (though
they do coalesce into a single throat in the static limit). The divergence
property of the null geodesics at the marginally anti-trapped surface
generalizes the ``flare-out'' condition for an arbitrary wormhole. We derive
theorems regarding violations of the null energy condition (NEC) at and near
these throats and find that, even for wormholes with arbitrary time-dependence,
the violation of the NEC is a generic property of wormhole throats. We also
discuss wormhole throats in the presence of fully antisymmetric torsion and
find that the energy condition violations cannot be dumped into the torsion
degrees of freedom. Finally by means of a concrete example we demonstrate that
even temporary suspension of energy-condition violations is incompatible with
the flare-out property of dynamic throats.Comment: 32 pages in plain LaTex, no figures. Additional text and references
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Vacuum polarization of a scalar field in wormhole spacetimes
An analitical approximation of for a scalar field in a static
spherically symmetric wormhole spacetime is obtained. The scalar field is
assumed to be both massive and massless, with an arbitrary coupling to
the scalar curvature, and in a zero temperature vacuum state.Comment: 10 pages, RevTeX, two eps figure
Static and dynamic traversable wormhole geometries satisfying the Ford-Roman constraints
It was shown by Ford and Roman in 1996 that quantum field theory severely
constrains wormhole geometries on a macroscopic scale. The first part of this
paper discusses a wide class of wormhole solutions that meet these constraints.
The type of shape function used is essentially generic. The constraints are
then discussed in conjunction with various redshift functions. Violations of
the weak energy condition and traversability criteria are also considered. The
second part of the paper analyzes analogous time-dependent (dynamic) wormholes
with the aid of differential forms. It is shown that a violation of the weak
energy condition is not likely to be avoidable even temporarily.Comment: 16 pages AMSTe
On Traversable Lorentzian Wormholes in the Vacuum Low Energy Effective String Theory in Einstein and Jordan Frames
Three new classes (II-IV) of solutions of the vacuum low energy effective
string theory in four dimensions are derived. Wormhole solutions are
investigated in those solutions including the class I case both in the Einstein
and in the Jordan (string) frame. It turns out that, of the eight classes of
solutions investigated (four in the Einstein frame and four in the
corresponding string frame), massive Lorentzian traversable wormholes exist in
five classes. Nontrivial massless limit exists only in class I Einstein frame
solution while none at all exists in the string frame. An investigation of test
scalar charge motion in the class I solution in the two frames is carried out
by using the Plebanski-Sawicki theorem. A curious consequence is that the
motion around the extremal zero (Keplerian) mass configuration leads, as a
result of scalar-scalar interaction, to a new hypothetical "mass" that confines
test scalar charges in bound orbits, but does not interact with neutral test
particles.Comment: 18 page
Electromagnetic waves in a wormhole geometry
We investigate the propagation of electromagnetic waves through a static
wormhole. It is shown that the problem can be reduced to a one-dimensional
Schr\"odinger-like equation with a barrier-type potential. Using numerical
methods, we calculate the transmission coefficient as a function of the energy.
We also discuss the polarization of the outgoing radiation due to this
gravitational scattering.Comment: LaTex file, 5 pages, 2 figures, one reference added, accepted for
publication in PR
Cylindrical thin-shell wormholes
A general formalism for the dynamics of non rotating cylindrical thin-shell
wormholes is developed. The time evolution of the throat is explicitly obtained
for thin-shell wormholes whose metric has the form associated to local cosmic
strings. It is found that the throat collapses to zero radius, remains static
or expands forever, depending only on the sign of its initial velocity.Comment: 10 page
Microlensing by natural wormholes: theory and simulations
We provide an in depth study of the theoretical peculiarities that arise in
effective negative mass lensing, both for the case of a point mass lens and
source, and for extended source situations. We describe novel observational
signatures arising in the case of a source lensed by a negative mass. We show
that a negative mass lens produces total or partial eclipse of the source in
the umbra region and also show that the usual Shapiro time delay is replaced
with an equivalent time gain. We describe these features both theoretically, as
well as through numerical simulations. We provide negative mass microlensing
simulations for various intensity profiles and discuss the differences between
them. The light curves for microlensing events are presented and contrasted
with those due to lensing produced by normal matter. Presence or absence of
these features in the observed microlensing events can shed light on the
existence of natural wormholes in the Universe.Comment: 16 pages, 24 postscript figures (3 coloured), revtex style, submitted
to Phys. Rev.
Thin-shell wormholes in Einstein-Maxwell theory with a Gauss-Bonnet term
We study five dimensional thin-shell wormholes in Einstein-Maxwell theory
with a Gauss-Bonnet term. The linearized stability under radial perturbations
and the amount of exotic matter are analyzed as a function of the parameters of
the model. We find that the inclusion of the quadratic correction substantially
widens the range of possible stable configurations, and besides it allows for a
reduction of the exotic matter required to construct the wormholes.Comment: 13 pages, 6 figures; v2: minor changes and new references added.
Accepted for publication in General Relativity and Gravitatio
Possible wormholes in a brane world
The condition R=0, where R is the four-dimensional scalar curvature, is used
for obtaining a large class (with an arbitrary function of r) of static,
spherically symmetric Lorentzian wormhole metrics. The wormholes are globally
regular and traversable, can have throats of arbitrary size and can be both
symmetric and asymmetric. These metrics may be treated as possible wormhole
solutions in a brane world since they satisfy the vacuum Einstein equations on
the brane where effective stress-energy is induced by interaction with the bulk
gravitational field. Some particular examples are discussed.Comment: 7 pages, revtex4. Submitted to Phys. Rev.
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