265 research outputs found
Towards the entropy of gravity time-dependent models via the Cardy-Verlinde formula
For models with several time-dependent components generalized entropies can
be defined. This is shown for the Bianchi type IX model. We first derive the
Cardy-Verlinde formula under the assumption that the first law of
thermodynamics is valid. This leads to an explicit expression of the total
entropy associated with this type of universes. Assuming the validity of the
Cardy entropy formula, we obtain expressions for the corresponding Bekenstein,
Bekenstein-Hawking and Hubble entropies. We discuss the validity of the
Cardy-Verlinde formula and possible extensions of the outlined procedure to
other time-dependent models.Comment: 13 page
A Note on Solitons in Brane Worlds
We obtain the zero mode effective action for gravitating objects in the bulk
of dilatonic domain walls. Without additional fields included in the bulk
action, the zero mode effective action reproduces the action in one lower
dimensions obtained through the ordinary Kaluza-Klein (KK) compactification,
only when the transverse (to the domain wall) component of the bulk metric does
not have non-trivial term depending on the domain wall worldvolume coordinates.
With additional fields included in the bulk action, non-trivial dependence of
the transverse metric component on the domain wall worldvolume coordinates
appears to be essential in reproducing the lower-dimensional action obtained
via the ordinary KK compactification. We find, in particular, that the
effective action for the charged (p+1)-brane in the domain wall bulk reproduces
the action for the p-brane in one lower dimensions.Comment: 13 pages, LaTe
Probing partially localized supergravity background of fundamental string ending on Dp-brane
We study the dynamics of the probe fundamental string in the field background
of the partially localized supergravity solution for the fundamental string
ending on Dp-brane. We separately analyze the probe dynamics for its motion
along the worldvolume direction and the transverse direction of the source
Dp-brane. We compare the dynamics of the probe along the Dp-brane worldvolume
direction to the BIon dynamics.Comment: 20 pages, LaTeX, revised version to appear in Phys. Rev.
Dilatonic p-Branes and Brane Worlds
We study a general dilatonic p-brane solution in arbitrary dimensions in
relation to the Randall-Sundrum scenario. When the p-brane is fully localized
along its transverse directions, the Kaluza-Klein zero mode of bulk graviton is
not normalizable. When the p-brane is delocalized along its transverse
directions except one, the Kaluza-Klein zero mode of bulk graviton is
normalizable if the warp factor is chosen to increase, in which case there are
singularities at finite distance away from the p-brane. Such delocalized
p-brane can be regarded as a dilatonic domain wall as seen in higher
dimensions. This unusual property of the warp factor allows one to avoid a
problem of dilatonic domain wall with decreasing warp factor that free massive
particles are repelled from the domain wall and hit singularities, since
massive particles with finite energy are trapped around delocalized p-branes
with increasing warp factor by gravitational force and can never reach the
singularities.Comment: 13 pages, LaTe
Pheromoneâmediated mating disruption in the millet stem borer, \u3ci\u3eConiesta ignefusalis\u3c/i\u3e (Lepidoptera: Pyralidae)
The millet stem borer, Coniesta ignefusalis Hampson (Lepidoptera: Pyralidae), is a major pest of pearl millet in the Sahelian region of Africa. The female sex pheromone has been identified and synthesized, and previous research had shown that the synthetic pheromone could cause high levels of reproductive communication disruption in small plots when released at rates of 640 mg/ha/day, using PVC resin formulation renewed every seven days to maintain efficiency. In the present research, in experiments in farmersâ fields in Niger, 86.8% (SE = 2.6%) communication disruption was achieved when polyethylene vials loaded with 0.5 mg pheromone at 400 dispensers/ha were used and replaced every 21 days. Polyethylene vials loaded with 80 mg pheromone gave uniform, zeroâorder release at approximately 0.05 mg/day at 27 °C. Experiments carried out on replicated 0.5 ha plots in farmersâ fields in Niger using a single application of these dispensers at 400 dispensers/ha resulted in at least 99% suppression of pheromone trap catches of male C. ignefusalis moths in treated plots relative to numbers in untreated plots for up to 3 months. However, sampling the central portions of these plots before and after harvest showed no significant differences in infestation, damage or yield loss between plots treated with pheromone and untreated plots. This may have been because of small plot size and the immigration of mated female moths into the treated plots which negated any reduction of mating of females within the treated plots. Comparisons of numbers of male C. ignefusalis moths in traps baited with the standard 0.5 mg monitoring lures and those baited with the 80 mg disruption dispensers showed catches in the latter were only 10â20% of those in the former; indicating high level communication disruptions in traps with high dose dispensers. Implications of using insect synthetic pheromones in the development of integrated management of C. ignefusalis in pearl millet cropping systems in the Sahel are discussed
Dark Viscous Fluid coupled with Dark Matter and future singularity
We study effects of viscous fluid coupled with dark matter in our universe.
We consider bulk viscosity in the cosmic fluid and we suppose the existence of
a coupling between fluid and dark matter, in order to reproduce a stable de
Sitter universe protected against future-time singularities. More general
inhomogeneous fluids are studied related to future singularities.Comment: 11 page
Geodesics and Newton's Law in Brane Backgrounds
In brane world models our universe is considered as a brane imbedded into a
higher dimensional space. We discuss the behaviour of geodesics in the
Randall-Sundrum background and point out that free massive particles cannot
move along the brane only. The brane is repulsive, and matter will be expelled
from the brane into the extra dimension. This is rather undesirable, and hence
we study an alternative model with a non-compact extra dimension, but with an
attractive brane embedded into the higher dimensional space. We study the
linearized gravity equations and show that Newton's gravitational law is valid
on the brane also in the alternative background.Comment: 14 page
Entropy and universality of Cardy-Verlinde formula in dark energy universe
We study the entropy of a FRW universe filled with dark energy (cosmological
constant, quintessence or phantom). For general or time-dependent equation of
state the entropy is expressed in terms of energy, Casimir energy,
and . The correspondent expression reminds one about 2d CFT entropy only for
conformal matter. At the same time, the cosmological Cardy-Verlinde formula
relating three typical FRW universe entropies remains to be universal for any
type of matter. The same conclusions hold in modified gravity which represents
gravitational alternative for dark energy and which contains terms growing at
low curvature. It is interesting that BHs in modified gravity are more entropic
than in Einstein gravity. Finally, some hydrodynamical examples testing new
shear viscosity bound, which is expected to be the consequence of the
holographic entropy bound, are presented for the early universe in the plasma
era and for the Kasner metric. It seems that the Kasner metric provides a
counterexample to the new shear viscosity bound.Comment: LaTeX file, 39 pages, references are adde
Inflationary Cosmologies in an Anisotropic Brane World
A new cosmological solution of the gravitational field equations in the
generalized Randall-Sundrum model for an anisotropic brane with Bianchi I
geometry and with perfect fluid as matter sources is presented. The matter is
described by a scalar field. The solution admits inflationary era and at a
later epoch the anisotropy of the universe washes out. We obtain two classes of
cosmological scenario, in the first case universe evolves from singularity and
in the second case universe expands without singularity.Comment: 15 pages, no figures, LaTe
Classical and Quantum Analysis of Repulsive Singularities in Four Dimensional Extended Supergravity
Non--minimal repulsive singularities (``repulsons'') in extended supergravity
theories are investigated. The short distance antigravity properties of the
repulsons are tested at the classical and the quantum level by a scalar
test--particle. Using a partial wave expansion it is shown that the particle
gets totally reflected at the origin. A high frequency incoming particle
undergoes a phase shift of . However, the phase shift for a
low--frequency particle depends upon the physical data of the repulson. The
curvature singularity at a finite distance turns out to be transparent
for the scalar test--particle and the coordinate singularity at the origin
serves as a repulsive barrier at which particles bounce off.Comment: 20 pages, 14 figure
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