1,987 research outputs found
Second order brane cosmology with radion stabilization
We study cosmology in the five-dimensional Randall-Sundrum brane-world with a
stabilizing effective potential for the radion and matter localized on the
branes. The analysis is performed by employing a perturbative expansion in the
ratio rho/V between the matter energy density on the branes and the brane
tensions around the static Randall-Sundrum solution (which has rho=0 and brane
tensions +-V). This approach ensures that the matter evolves adiabatically and
allows us to find approximate solutions to second order in \rho/V. Some
particular cases are then analyzed in details.Comment: 17 pages, RevTeX4, 4 figures, final version to appear in Phys. Rev.
Fractal extra dimension in Kaluza-Klein theory
Kaluza-Klein theory in which the geometry of an additional dimension is
fractal has been considered. In such a theory the mass of an elementary
electric charge appears to be many orders of magnitude smaller than the Planck
mass, and the "tower" of masses which correspond to higher integer charges
becomes aperiodic.Comment: 3 pages, accepted for publication in Phys.Rev.D (submitted on
3.28.2001
Minimal Universal Extra Dimensions
Highly degenerate spectra associated with universal extra dimensions (UED)
provide an interesting phenomenology not only from the point of view of
cosmology and astrophysics, but also for colliders. We study these exotic
signals for the simplest case, called minimal UED, where it is natural to find
slow charged particles, displaced vertices, tracks with non-vanishing impact
parameters, track kinks, and even vanishing charged tracks.Comment: 6 pages, 3 figures. Contributed to XXIII International Symposium on
Lepton and Photon Interactions at High Energy, Aug 13-18, 2007, Daegu, Kore
Non Abelian gauge symmetries induced by the unobservability of extra-dimensions in a Kaluza-Klein approach
In this work we deal with the extension of the Kaluza-Klein approach to a
non-Abelian gauge theory; we show how we need to consider the link between the
n-dimensional model and a four-dimensional observer physics, in order to
reproduce fields equations and gauge transformations in the four-dimensional
picture. More precisely, in fields equations any dependence on
extra-coordinates is canceled out by an integration, as consequence of the
unobservability of extra-dimensions. Thus, by virtue of this extra-dimensions
unobservability, we are able to recast the multidimensional Einstein equations
into the four-dimensional Einstein-Yang-Mills ones, as well as all the right
gauge transformations of fields are induced. The same analysis is performed for
the Dirac equation describing the dynamics of the matter fields and, again, the
gauge coupling with Yang-Mills fields are inferred from the multidimensional
free fields theory, together with the proper spinors transformations.Comment: 5 pages, no figures, to appear in Mod. Phys. Lett.
The Proliferation REduction with Vascular ENergy Trial (PREVENT)
PREVENT was the first prospective, randomized placebo-controlled study of intracoronary beta radiotherapy with (32)P. A total of 105 patients with de novo or restenotic lesions, treated by stenting or balloon angioplasty, received 0 (control), 16, 20, or 24 Gy to a depth of 1 mm beyond the lumen surface. Rates of restenosis (50% diameter stenosis or more) were significantly lower in radiotherapy patients at the target site (8% compared with 39%, P = 0.012) and at the target site plus adjacent segments (22% compared with 50%, P = 0.018). Stenosis adjacent to the target site and late thrombotic events reduced the overall clinical benefit of radiotherapy
Human Dynamics: The Correspondence Patterns of Darwin and Einstein
While living in different historical era, Charles Darwin (1809-1882) and
Albert Einstein (1879-1955) were both prolific correspondents: Darwin sent
(received) at least 7,591 (6,530) letters during his lifetime while Einstein
sent (received) over 14,500 (16,200). Before email scientists were part of an
extensive university of letters, the main venue for exchanging new ideas and
results. But were the communication patterns of the pre-email times any
different from the current era of instant access? Here we show that while the
means have changed, the communication dynamics has not: Darwin's and Einstein's
pattern of correspondence and today's electronic exchanges follow the same
scaling laws. Their communication belongs, however, to a different universality
class from email communication, providing evidence for a new class of phenomena
capturing human dynamics.Comment: Supplementary Information available at http://www.nd.edu/~network
The embedding of the spacetime in five-dimensional spaces with arbitrary non-degenerate Ricci tensor
We discuss and prove a theorem which asserts that any n-dimensional
semi-Riemannian manifold can be locally embedded in a (n+1)-dimensional space
with a non-degenerate Ricci tensor which is equal, up to a local analytic
diffeomorphism, to the Ricci tensor of an arbitrary specified space. This may
be regarded as a further extension of the Campbell-Magaard theorem. We
highlight the significance of embedding theorems of increasing degrees of
generality in the context of higher dimensional spacetimes theories and
illustrate the new theorem by establishing the embedding of a general class of
Ricci-flat spacetimes
Reconstruction of Cosmological Models From Equation of State of Dark Energy
We consider a class of five-dimensional cosmological solutions which contains
two arbitrary function and . We found that the arbitrary
function contained in the solutions can be rewritten in terms of the
redshift as a new arbitrary function . We further showed that this
new arbitrary function could be solved out for four known parameterized
equations of state of dark energy. Then the models can be reconstructed
and the evolution of the density and deceleration parameters of the universe
can be determined.Comment: 10 pages, 4 eps figures, ws-ijmpd.cls styl
The fate of the zero mode of the five-dimensional kink in the presence of gravity
We investigate what becomes of the translational zero-mode of a
five-dimensional domain wall in the presence of gravity, studying the scalar
perturbations of a thick gravitating domain wall with AdS asymptotics and a
well-defined zero-gravity limit. Our analysis reveals the presence of a wide
resonance which can be seen as a remnant of the translational zero-mode present
in the domain wall in the absence of gravity and which ensures a continuous
change of the physical quantities (such as e.g. static potential between
sources) when the Planck mass is sent to infinity. Provided that the thickness
of the wall is much smaller than the AdS radius of the space-time, the
parameters of this resonance do not depend on details of the domain wall's
structure, but solely on the geometry of the space-time.Comment: 29 pages, 4 figures; v2: 2 machine-generated typos in the
introduction correcte
Dimensional Reduction without Extra Continuous Dimensions
We describe a novel approach to dimensional reduction in classical field
theory. Inspired by ideas from noncommutative geometry, we introduce extended
algebras of differential forms over space-time, generalized exterior
derivatives and generalized connections associated with the "geometry" of
space-times with discrete extra dimensions. We apply our formalism to theories
of gauge- and gravitational fields and find natural geometrical origins for an
axion- and a dilaton field, as well as a Higgs field.Comment: 23 page
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