135 research outputs found
Brane World Cosmology In Jordan-Brans-Dicke Theory
We consider the embedding of 3+1 dimensional cosmology in 4+1 dimensional
Jordan-Brans-Dicke theory. We show that exponentially growing and power law
scale factors are implied. Whereas the 4+1 dimensional scalar field is
approximately constant for each, the effective 3+1 dimensional scalar field is
constant for exponentially growing scale factor and time dependent for power
law scale factor.Comment: 11 page
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.
Bouncing pre-big bang on the brane
A regular bouncing universe is obtained in the context of a dilaton-gravity
brane world scenario. The scale factor starts in a contracting inflationary
phase both in the Einstein and in the string frame, it then undergoes a bounce
(due to interaction with the bulk Weyl tensor), and subsequently enters into a
decelerated expanding era. This graceful exit is obtained at low curvature and
low coupling, and without violating the Null Energy Condition.Comment: 16 pages, 3 figures; final version to be published on PRD. General
improvement of section II (better specification of the matter content on the
brane and discussion about the late time behavior), main results unchanged; 2
references adde
Modified Brans-Dicke theory of gravity from five-dimensional vacuum
We investigate, in the context of five-dimensional (5D) Brans-Dicke theory of
gravity, the idea that macroscopic matter configurations can be generated from
pure vacuum in five dimensions, an approach first proposed in the framework of
general relativity. We show that the 5D Brans-Dicke vacuum equations when
reduced to four dimensions lead to a modified version of Brans-Dicke theory in
four dimensions (4D). As an application of the formalism, we obtain two
five-dimensional extensions of four-dimensional O'Hanlon and Tupper vacuum
solution and show that they lead two different cosmological scenarios in 4D.Comment: 9 page
Smooth hybrid inflation in supergravity with a running spectral index and early star formation
It is shown that in a smooth hybrid inflation model in supergravity adiabatic
fluctuations with a running spectral index with \ns >1 on a large scale and
\ns <1 on a smaller scale can be naturally generated, as favored by the
first-year data of WMAP. It is due to the balance between the nonrenormalizable
term in the superpotential and the supergravity effect. However, since smooth
hybrid inflation does not last long enough to reproduce the central value of
observation, we invoke new inflation after the first inflation. Its initial
condition is set dynamically during smooth hybrid inflation and the spectrum of
fluctuations generated in this regime can have an appropriate shape to realize
early star formation as found by WMAP. Hence two new features of WMAP
observations are theoretically explained in a unified manner.Comment: 12 pages, 1 figure, to appear in Phys. Rev.
Fine-Tuning Solution for Hybrid Inflation in Dissipative Chaotic Dynamics
We study the presence of chaotic behavior in phase space in the
pre-inflationary stage of hybrid inflation models. This is closely related to
the problem of initial conditions associated to these inflationary type of
models. We then show how an expected dissipative dynamics of fields just before
the onset of inflation can solve or ease considerably the problem of initial
conditions, driving naturally the system towards inflation. The chaotic
behavior of the corresponding dynamical system is studied by the computation of
the fractal dimension of the boundary, in phase space, separating inflationary
from non-inflationary trajectories. The fractal dimension for this boundary is
determined as a function of the dissipation coefficients appearing in the
effective equations of motion for the fields.Comment: 10 pages, 4 eps figures (uses epsf), Revtex. Replaced with version to
match one in press Physical Review
Pre-big bang on the brane
The equations of motion and junction conditions for a gravi-dilaton brane
world scenario are studied in the string frame. It is shown that they allow
Kasner-like solutions on the brane, which makes the dynamics of the brane very
similar to the low curvature phase of pre-big bang cosmology. Analogies and
differences of this scenario with the Randall-Sundrum one and with the standard
bulk pre-big bang dynamics are also discussed.Comment: Final version published on PRD; one reference adde
Anatomical and histological characteristics of teeth in agouti (Dasyprocta prymnolopha Wagler, 1831)
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