224 research outputs found
Consistent ADD scenario with stabilized extra dimension
A model with one compact extra dimension and a scalar field of Brans-Dicke
type in the bulk is discussed. It describes two branes with non-zero tension
embedded into the space-time with flat background. This setup allows one to use
a very simple method for stabilization of the size of extra dimension. It
appears that the four-dimensional Planck mass is expressed only through
parameters of the scalar field potentials on the branes.Comment: 11 pages, LaTeX, enlarged content, corrected typo
Hierarchy problem and the cosmological constant in a five-dimensional Brans-Dicke brane world model
We discuss a new solution, admitting the existence of dS_{4} branes, in
five-dimensional Brans-Dicke theory. It is shown that, due to a special form of
a bulk scalar field potential, for certain values of the model parameters the
effective cosmological constant can be made small on the brane, where the
hierarchy problem of gravitational interaction is solved. We also discuss new
stabilization mechanism which is based on the use of auxiliary fields.Comment: 11 page
Supergravity Inflation on the Brane
We study N=1 Supergravity inflation in the context of the braneworld
scenario. Particular attention is paid to the problem of the onset of inflation
at sub-Planckian field values and the ensued inflationary observables. We find
that the so-called -problem encountered in supergravity inspired
inflationary models can be solved in the context of the braneworld scenario,
for some range of the parameters involved. Furthermore, we obtain an upper
bound on the scale of the fifth dimension, M_5 \lsim 10^{-3} M_P, in case the
inflationary potential is quadratic in the inflaton field, . If the
inflationary potential is cubic in , consistency with observational data
requires that .Comment: 6 pages, 1 figure, to appear in Phys. Rev.
Alphaviruses detected in mosquitoes in the North-Eastern regions of South Africa, 2014 to 2018
The prevalence and distribution of African alphaviruses such as chikungunya have increased in recent years. Therefore, a better understanding of the local distribution of alphaviruses in vectors across the African continent is important. Here, entomological surveillance was performed from 2014 to 2018 at selected sites in north-eastern parts of South Africa where alphaviruses have been identified during outbreaks in humans and animals in the past. Mosquitoes were collected using a net, CDC-light, and BG-traps. An alphavirus genus-specific nested RT-PCR was used for screening, and positive pools were confirmed by sequencing and phylogenetic analysis. We collected 64,603 mosquitoes from 11 genera, of which 39,035 females were tested. Overall, 1462 mosquito pools were tested, of which 21 were positive for alphaviruses. Sindbis (61.9%, N = 13) and Middelburg (28.6%, N = 6) viruses were the most prevalent. Ndumu virus was detected in two pools (9.5%, N = 2). No chikungunya positive pools were identified. Arboviral activity was concentrated in peri-urban, rural, and conservation areas. A range of Culicidae species, including Culex univittatus, Cx. pipiens s.l., Aedes durbanensis, and the Ae. dentatus group, were identified as potential vectors. These findings confirm the active circulation and distribution of alphaviruses in regions where human or animal infections were identified in South Africa.Environmental Biolog
Can we live in a self-tuning universe?
The self-tuning brane scenario is an attempt to solve the cosmological
constant problem in the context of extra dimensions. Rather than making the
vacuum energy small, this approach proceeds by removing the gravitational
effect of vacuum energy on the expansion of the universe. Such behavior is only
possible through changing the Friedmann equation of conventional cosmology, and
we discuss difficulties in obtaining cosmological evolution compatible with
observation in this context. Specific models considered include a bulk scalar
field coupling to the brane via a conformal transformation of the brane metric,
and via a rescaling of the brane volume element
Perturbations of brane worlds
We consider cosmological models where the universe, governed by Einstein's
equations, is a piece of a five dimensional double-sided anti-de Sitter
spacetime (that is, a "-symmetric bulk") with matter confined to its four
dimensional Robertson-Walker boundary or "brane". We study the perturbations of
such models. We use conformally minkowskian coordinates to disentangle the
contributions of the bulk gravitons and of the motion of the brane. We find the
restrictions put on the bulk gravitons when matter on the brane is taken to be
a scalar field and we solve in that case the brane perturbation equations.Comment: 19 pages, no figures, RevTex, version to appear in Phys.Rev.D; minor
changes in chap.V, polarisation tensor at page 13 correcte
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