9,178 research outputs found
Exact dynamical AdS black holes and wormholes with a Klein-Gordon field
We present several classes of exact solutions in the Einstein-Klein-Gordon
system with a cosmological constant. The spacetime has spherical, plane, or
hyperbolic symmetry and the higher-dimensional solutions are obtained in a
closed form only in the plane symmetric case. Among them, the class-I solution
represents an asymptotically locally anti-de Sitter (AdS) dynamical black hole
or wormhole. In four and higher dimensions, the generalized Misner-Sharp
quasi-local mass blows up at AdS infinity, inferring that the spacetime is only
locally AdS. In three dimensions, the scalar field becomes trivial and the
solution reduces to the BTZ black hole.Comment: 11 pages, 2 figures, 2 tables; v2, results strengthened, argument on
trapping horizon corrected; v3, argument on locally AdS property added,
accepted for publication in Physical Review
Asymptotically Friedmann self-similar scalar field solutions with potential
We investigate self-similar solutions which are asymptotic to the Friedmann
universe at spatial infinity and contain a scalar field with potential. The
potential is required to be exponential by self-similarity. It is found that
there are two distinct one-parameter families of asymptotic solutions,one is
asymptotic to the proper Friedmann universe, while the other is asymptotic to
the quasi-Friedmann universe, i.e., the Friedmann universe with anomalous solid
angle. The asymptotically proper Friedmann solution is possible only if the
universe is accelerated or the potential is negative. If the potential is
positive, the density perturbation in the asymptotically proper Friedmann
solution rapidly falls off at spatial infinity, while the mass perturbation is
compensated. In the asymptotically quasi-Friedmann solution, the density
perturbation falls off only in proportion to the inverse square of the areal
radius and the relative mass perturbation approaches a nonzero constant at
spatial infinity. The present result shows that a necessary condition holds in
order that a self-gravitating body grows self-similarly due to the constant
accretion of quintessence in an accelerating universe.Comment: accepted for publication in Physical Review D, minor correction,
typos correcte
Absence of non-linear Meissner effect in YBa2Cu3O6.95
We present measurements the field and temperature dependence of the
penetration depth (lambda) in high purity, untwinned single crystals of
YBa2Cu3O6.95 in all three crystallographic directions. The temperature
dependence of lambda is linear down to low temperatures, showing that our
crystals are extremely clean. Both the magnitude and temperature dependence of
the field dependent correction to lambda however, are considerably different
from that predicted from the theory of the non-linear Meissner effect for a
d-wave superconductor (Yip-Sauls theory). Our results suggest that the
Yip-Sauls effect is either absent or is unobservably small in the Meissner
state of YBa2Cu3O6.95.Comment: 4 pages, 4 figures (Latex file + Postscipt figures
Crescimento de Eucalyptus benthamii submetido à aplicação de lama de cal e cinza de madeira.
bitstream/item/145220/1/CT-373-Maeda.pd
Black-hole dynamics in BHT massive gravity
Using an exact Vaidya-type null-dust solution, we study the area and entropy
laws for dynamical black holes defined by a future outer trapping horizon in
(2+1)-dimensional Bergshoeff-Hohm-Townsend (BHT) massive gravity. We consider
the theory admitting a degenerate (anti-)de Sitter vacuum and pure BHT gravity.
It is shown that, while the area of a black hole decreases by the injection of
a null dust with positive energy density in several cases, the Wald-Kodama
dynamical entropy always increases.Comment: 7 pages, 1 figur
Symmetry Reduction by Lifting for Maps
We study diffeomorphisms that have one-parameter families of continuous
symmetries. For general maps, in contrast to the symplectic case, existence of
a symmetry no longer implies existence of an invariant. Conversely, a map with
an invariant need not have a symmetry. We show that when a symmetry flow has a
global Poincar\'{e} section there are coordinates in which the map takes a
reduced, skew-product form, and hence allows for reduction of dimensionality.
We show that the reduction of a volume-preserving map again is volume
preserving. Finally we sharpen the Noether theorem for symplectic maps. A
number of illustrative examples are discussed and the method is compared with
traditional reduction techniques.Comment: laTeX, 31 pages, 5 figure
Warped compactification on curved manifolds
The characterization of a six- (or seven)-dimensional internal manifold with
metric as having positive, zero or negative curvature is expected to be an
important aspect of warped compactifications in supergravity. In this context,
Douglas and Kallosh recently pointed out that a compact internal space with
negative curvature could help to construct four-dimensional de Sitter solutions
only if the extra dimensions are strongly warped or there are large stringy
corrections. That is, the problem of finding 4-dimensional de Sitter solutions
is well posed, if all extra dimensions are physically compact, which is called
a no-go theorem. Here, we show that the above conclusion does not extend to a
general class of warped compactifications in classical supergravity that allow
a non-compact direction or cosmological solutions for which the internal space
is asymptotic to a cone over a product of compact Einstein spaces or spheres.
For clarity, we present classical solutions that compactify higher-dimensional
spacetime to produce a Robertson--Walker universe with de Sitter-type expansion
plus one extra non-compact direction. Such models are found to admit both an
effective four-dimensional Newton constant that remains finite and a
normalizable zero-mode graviton wavefunction. We also exhibit the possibility
of obtaining 4D de Sitter solutions by including the effect of fluxes (p-form
field strengths).Comment: 24 pages, 1 figure; v5 significant changes in the presentation,
published (journal) versio
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