318 research outputs found
Thin-shell wormholes: Linearization stability
The class of spherically-symmetric thin-shell wormholes provides a
particularly elegant collection of exemplars for the study of traversable
Lorentzian wormholes. In the present paper we consider linearized (spherically
symmetric) perturbations around some assumed static solution of the Einstein
field equations. This permits us to relate stability issues to the (linearized)
equation of state of the exotic matter which is located at the wormhole throat.Comment: 4 pages; ReV_TeX 3.0; one postscript figur
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
Do as We Say: Funders’ Invisible Hold Over Research
This roundtable is an open discussion of the commercialization of academic work, namely how funders’ expectations have the possibility of driving research outcomes. By exploring the possible ramifications the expectations funders have of our research outcomes, we can avoid contributing to the increasing commercialization of researc
The Effect of Negative-Energy Shells on the Schwarzschild Black Hole
We construct Penrose diagrams for Schwarzschild spacetimes joined by massless
shells of matter, in the process correcting minor flaws in the similar diagrams
drawn by Dray and 't Hooft, and confirming their result that such shells
generate a horizon shift. We then consider shells with negative energy density,
showing that the horizon shift in this case allows for travel between the
heretofore causally separated exterior regions of the Schwarzschild geometry.
These drawing techniques are then used to investigate the properties of
successive shells, joining multiple Schwarzschild regions. Again, the presence
of negative-energy shells leads to a causal connection between the exterior
regions, even in (some) cases with two successive shells of equal but opposite
total energy.Comment: 12 pages, 10 figure
Relevance of unilateral and bilateral sexual polyploidization in relation to intergenomic recombination and introgression in Lilium species hybrids
Sexual polyploids were induced in diploid (2n = 2x = 24) interspecific F1 hybrids of Longiflorum × Asiatic (LA) and Oriental × Asiatic (OA) Lilium hybrids by backcrossing to Asiatic (AA) parents as well as by sib-mating of the F1 LA hybrids. A majority of the BC1 progenies were triploid and the progenies from sib-mating were tetraploid or near tetraploids. Genomic in situ hybridization (GISH) technique was applied to assess the intergenomic recombination in the BC1 populations of LA and OA hybrids obtained after unilateral sexual polyploidization. A total of 63 LA (LA × AA and AA × LA) and 53 OA hybrids were analysed. LA hybrids were originated through the functioning of 2n gametes either as 2n eggs or 2n pollen while those of OA hybrids originated through functional 2n pollen of diploid OA genotype. In both type of crosses, a majority of the progenies had originated through First Division Restitution (FDR) mechanism of functional 2n gamete either with or without a cross over. However, there were nine LA- and four OA-genotypes where Indeterminate Meiotic Restitution (IMR) was the mechanism of 2n gamete formation. Based on GISH, total amount of introgression of Longiflorum and Oriental genome into Asiatic genome was determined. Most of the BC progenies exhibited recombination and the amount of recombination was higher in LA hybrids as compared to OA hybrids. Intergenomic recombination was also determined cytologically in the 16 plants of sib-mated LA hybrids where both parents had contributed 2n gametes. Based on these results the nature of interspecific lily hybrids obtained from uni- and bilateral sexual polyploidization leading to allotriploid and allotetraploid formation is discussed in the context of introgression and intergenomic recombinatio
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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Exactly soluble model for self-gravitating D-particles with the wormhole
We consider D-particles coupled to the CGHS dilaton gravity and obtain the
exact wormhole geometry and trajectories of D-particles by introducing the
exotic matter. The initial static wormhole background is not stable after
infalling D-particles due to the classical backreaction of the geometry so that
the additional exotic matter source should be introduced for the stability.
Then, the traversable wormhole geometry naturally appears and the D-particles
can travel through it safely. Finally, we discuss the dynamical evolution of
the wormhole throat and the massless limit of D-particles.Comment: 16 pages, 3 figures, revte
Wormhole phase in the RST model
We show that the RST model describing the exactly soluble black hole model
can have a dynamical wormhole solution along with an appropriate boundary
condition. The necessary exotic matter which is usually negative energy density
is remarkably produced by the quantization of the infalling matter fields. Then
the asymptotic geometry in the past is two-dimensional anti-de Sitter(AdS),
which implies the exotic matter is negative. As time goes on, the wormhole
eventually evolves into the black hole and its Hawking radiation appears. The
throat of the static RST wormhole is lower-bounded but in the presence of
infalling matter it collapses to a black hole.Comment: v1. REVTeX3, 12 pages and 1 figure; v2. JHEP3, 10 pages and 1 figure,
version published in JHE
A Comparison of the LVDP and {\Lambda}CDM Cosmological Models
We compare the cosmological kinematics obtained via our law of linearly
varying deceleration parameter (LVDP) with the kinematics obtained in the
{\Lambda}CDM model. We show that the LVDP model is almost indistinguishable
from the {\Lambda}CDM model up to the near future of our universe as far as the
current observations are concerned, though their predictions differ
tremendously into the far future.Comment: 6 pages, 5 figures, 1 table, matches the version to be published in
International Journal of Theoretical Physic
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