222 research outputs found
Equivalence Between Space-Time-Matter and Brane-World Theories
We study the relationship between space-time-matter (STM) and brane theories.
These two theories look very different at first sight, and have different
motivation for the introduction of a large extra dimension. However, we show
that they are equivalent to each other. First we demonstrate that STM predicts
local and non-local high-energy corrections to general relativity in 4D, which
are identical to those predicted by brane-world models. Secondly, we notice
that in brane models the usual matter in 4D is a consequence of the dependence
of five-dimensional metrics on the extra coordinate. If the 5D bulk metric is
independent of the extra dimension, then the brane is void of matter. Thus, in
brane theory matter and geometry are unified, which is exactly the paradigm
proposed in STM. Consequently, these two 5D theories share the same concepts
and predict the same physics. This is important not only from a theoretical
point of view, but also in practice. We propose to use a combination of both
methods to alleviate the difficult task of finding solutions on the brane. We
show an explicit example that illustrate the feasibility of our proposal.Comment: Typos corrected, three references added. To appear in Mod. Phys. Let
A Bestiary of Higher Dimensional Taub-NUT-AdS Spacetimes
We present a menagerie of solutions to the vacuum Einstein equations in six,
eight and ten dimensions. These solutions describe spacetimes which are either
locally asymptotically adS or locally asymptotically flat, and which have
non-trivial topology. We discuss the global structure of these solutions, and
their relevance within the context of M-theory.Comment: 11 pages, LaTex(v4: Comments and references added
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
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
Genuine Dyons in Born-Infeld Electrodynamics
Study of magnetic monopoles in the original version of Born-Infeld (BI)
electrodynamics is performed. It then is realized that interesting new physics
emerge and they include exotic behavior of radial electric monopole field such
as its regularity as and its changing behavior with the absence or
presence of the radial magnetic monopole field. This last point has been
interpreted as the manifestation of the existence of point-like dyons in
abelian BI theory. Two pieces of clear evidences in favor of this dyon
interpretation are provided. It is also demonstrated that despite these unique
features having no analogues in standard Maxwell theory, the cherished Dirac
quantisation condition remains unchanged. Lastly, comments are given concerning
that dyons found here in the original version of BI electrodynamics should be
distinguished from the ones with the same name or BIons being studied in the
recent literature on D-brane physics.Comment: 19 pages, Revtex, references added, no other change
Striga hermonthica Infection of Wild Pennisetum Germplasm is Related to Time of Flowering and Downy Mildew Incidence
Two hundred and seventy five wild P. glaucum subsp. monodii and subsp. stenostachyum (pearl millet) accessions were assessed for resistance to Striga hermonthica in Mali. Plots were artificially infested with S. hermonthica. Incidence of downy mildew (Sclerospora graminicola) infection was also assessed. Striga hermonthica emergence was lower on earlier flowering accessions and accessions with a high incidence of Sclerospora graminicola infection. Therefore, selection for Striga hermonthica resistance could be confounded by the relationships between Striga hermonthica emergence with flowering date and Sclerospora graminicola incidence. However, 54 entries were identified that had lower observed Striga hermonthica occurrence than the predicted value, based on days to flowering and Sclerospora graminicola incidence
Holographic Principle bounds on Primordial Black Hole abundances
The generalized Second Law of thermodynamics and the Holographic Principle
are combined to obtain the maximum mass of black holes formed inside a static
spherical box of size filled with radiation at initial temperature .
The final temperature after the formation of black holes is evaluated, and we
show that a critical threshold exists for the radiation to be fully consumed by
the process. We next argue that if some form of Holographic Principle holds,
upper bounds to the mass density of PBHs formed in the early universe may be
obtained. The limits are worked out for inflationary and non-inflationary
cosmological models. This method is independent of the known limits based on
the background fluxes (from cosmic rays, radiation and other forms of energy)
and applies to potentially important epochs of PBH formation, resulting in
quite strong constraints to .Comment: Latex file, 2 .ps figures. To appear in Classical and Quantum Gravit
Wave Mechanics and General Relativity: A Rapprochement
Using exact solutions, we show that it is in principle possible to regard
waves and particles as representations of the same underlying geometry, thereby
resolving the problem of wave-particle duality
Brane World Cosmologies with Varying Speed of Light
We study cosmologies in the Randall-Sundrum models, incorporating the
possibility of time-varying speed of light and Newton's constant. The
cosmologies with varying speed of light (VSL) were proposed by Moffat and by
Albrecht and Magueijo as an alternative to inflation for solving the
cosmological problems. We consider the case in which the speed of light varies
with time after the radion or the scale of the extra dimension has been
stabilized. We elaborate on the conditions under which the flatness problem and
the cosmological constant problem can be resolved. We find that the RS models
are more restrictive about possible desirable VSL cosmological models than the
standard general relativity. Particularly, the VSL cosmologies may provide with
a possible mechanism for bringing the quantum corrections to the fine-tuned
brane tensions after the SUSY breaking under control.Comment: 18 pages, LaTeX, revised version with minor corrections to appear in
Phys. Rev.
Probing the Holography of Near-Horizon AdS(5)xS(5) Geometry
Using the AdS/CFT correspondence we study the holographic principle and the
CFT/FRW relations in the near-horizon AdS(5)xS(5) geometry with a probe
D3-brane playing the role of the boundary to this space. The motion of the
probe D3-brane in the bulk, induces a cosmological evolution on the brane. As
the brane crosses the horizon of the bulk black hole, it probes the holography
of the dual CFT. We test the holographic principle and we find corrections to
CFT/FRW relations in various physical cases: for radially moving, spinning and
electrically charged D3-brane and for a NS/NS B-field in the bulk.Comment: LaTex file, 30 pages, no figures; major revision, new results
presented, references added; to appear in JCA
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