24,507 research outputs found
On the accretion of phantom energy onto wormholes
By using a properly generalized accretion formalism it is argued that the
accretion of phantom energy onto a wormhole does not make the size of the
wormhole throat to comovingly scale with the scale factor of the universe, but
instead induces an increase of that size so big that the wormhole can engulf
the universe itself before it reaches the big rip singularity, at least
relative to an asymptotic observer.Comment: 4 pages, LaTex, to appear in Phys. Lett.
On the formalism of dark energy accretion onto black- and worm-holes
In this work a general formalism for the accretion of dark energy onto
astronomical objects, black holes and wormholes, is considered. It is shown
that in models with four dimensions or more, any singularity with a divergence
in the Hubble parameter may be avoided by a big trip, if it is assumed that
there is no coupling between the bulk and this accreting object. If this is not
the case in more than four dimensions, the evolution of the cosmological object
depends on the particular model.Comment: 6 page
Tensorial perturbations in the bulk of inflating brane worlds
In this paper we consider the stability of some inflating brane-world models
in quantum cosmology. It is shown that whereas the singular model based on the
construction of inflating branes from Euclidean five-dimensional anti-de Sitter
space is unstable to tensorial cosmological perturbations in the bulk, the
nonsingular model which uses a five-dimensional asymptotically anti-de Sitter
wormhole to construct the inflating branes is stable to these perturbations.Comment: 4 pages, RevTex, to appear in Phys. Rev.
A new species of Hormathia (Actiniaria, Hormathiidae) from the eastern Weddell Sea, Antarctica
A new species of sea anemone in the genus
Hormathia, is described and illustrated based on fortytwo specimens collected during the Polarstern cruises
ANT XV/3 and ANT XVII/3 in the Weddell Sea. The
main features of the new taxon are the crown of flattened
and hooked tubercles at the distal end of the scapus, the
regular arrangement of pointed tubercles along the column and the cnidom. The new species shares the pointed
tubercles, at least in the upper part of the scapus, with
two other species of Hormathia in the southern hemisphere: Hormathia spinosa Hertwig 1882 and H. pectinata Hertwig 188
New record of the sea anemone Kadosactis antarctica (Carlgren, 1928): re-description of an Antarctic deep-sea sea anemone, and a discussion of its generic and familial placement
Sagartiogeton antarcticus Carlgren, 1928 is an
Antarctic deep-sea species of sea anemone only known
from its holotype. The species has been assigned to the
genera Sagartiogeton and Kadosactis, and is currently
placed within the family Kadosactidae Riemann-Zu¨rneck, 1991. Kadosactis antarctica is re-described based
on 11 specimens collected during the cruise of the R/V
Polarstern ANT XIX/3 (ANDEEP-I) to the Scotia Sea
and off the South Shetland Islands (Antarctica). The
description includes a complete account of cnidae and
photographs. Because the mesogloea is thickened on the
aboral surface on the base of the tentacles, this feature
becomes a generic character of Kadosactis rather than a
differential specific character among the species of the
genus as previously proposed. Furthermore, the known
distribution of the species is enlarged to include the
southern branch of the Scotia Sea
Stephanthus antarcticus, a new genus and species of sea anemone (Actiniaria, Haloclavidae) from the South Shetland Islands, Antarctica
Stephanthus antarcticus gen. nov. et sp. nov. is
described and illustrated from six specimens collected
in the Antarctic Peninsula on the Polarstern cruises
ANT XV/3 and ANT XIX/3. The new genus is characterised by the absence of sphincter and basilar musculature, the presence of a single strong siphonoglyph with a
basal enlargement, distinct parietobasilar musculature,
tentacles without acrospheres, two cycles of six pairs
of mesenteries (only one of them perfect), and a deep
fosse with parapet; another remarkable feature is the absence of microbasic p-mastigophores. The new genus
shows characteristics of three families of soft-bottomdwelling sea anemones, namely Haloclavidae Verrill,
1899, Halcampoididae Appellöf, 1896, and Andresiidae
Stephenson, 1922. The generic characters of Stephanthus
gen. nov. are discussed and it is tentatively placed in the
family Haloclavidae
The entangled accelerating universe
Using the known result that the nucleation of baby universes in correlated
pairs is equivalent to spacetime squeezing, we show in this letter that there
exists a T-duality symmetry between two-dimensional warp drives, which are
physically expressible as localized de Sitter little universes, and two
dimensional Tolman-Hawking and Gidding-Strominger baby universes respectively
correlated in pairs, so that the creation of warp drives is also equivalent to
spacetime squeezing. Perhaps more importantly, it has been also seen that the
nucleation of warp drives entails a violation of the Bell's inequalities, and
hence the phenomena of quantum entanglement, complementarity and wave function
collapse. These results are generalized to the case of any dynamically
accelerating universe filled with dark or phantom energy whose creation is also
physically equivalent to spacetime squeezing and to the violation of the Bell's
inequalities, so that the universe we are living in should be governed by
essential sharp quantum theory laws and must be a quantum entangled system
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