9 research outputs found
Friedmann universe with dust and scalar field
We study a spatially flat Friedmann model containing a pressureless perfect
fluid (dust) and a scalar field with an unbounded from below potential of the
form V(\fii)=W_0 - V_0\sinh(\sqrt{3/2}\kappa\fii), where the parameters
and are arbitrary and . The model is
integrable and all exact solutions describe the recollapsing universe. The
behavior of the model near both initial and final points of evolution is
analyzed. The model is consistent with the observational parameters. We single
out the exact solution with the present-day values of acceleration parameter
and dark matter density parameter describing
the evolution within the time approximately equal to .Comment: 11 pages, 10 figure
6D thick branes from interacting scalar fields
A thick brane in six dimensions is constructed using two scalar fields. The
field equations for 6D gravity plus the scalar fields are solved numerically.
This thick brane solution shares some features with a previously studied
analytic solutions, but has the advantage that the energy-momentum tensor which
forms the thick brane comes from the scalar fields rather than being put in by
hand. Additionally the scalar fields which form the brane also provide a
universal, non-gravitational trapping mechanism for test fields of various
spins.Comment: final versio
Anti-de-Sitter Island-Universes from 5D Standing Waves
We construct simple standing wave solutions in a 5D space-time with a ghost
scalar field. The nodes of these standing waves are 'islands' of 4D Minkowski
space-time. For the 5D model with increasing (decreasing) warp factor there are
a finite (infinite) number of nodes and thus Minkowski island-universes having
different parameters, such as gravitational and cosmological constants. This
feature is similar to the assumptions of the landscape models, which postulate
a large number of universes with different parameters. This standing wave
solution also provides a new localization mechanism - matter fields can reside
only on Minkowski 'islands', where the background space-time does not
oscillate.Comment: 14 page pre-print format. Discussion about connection to Weyl gravity
added and "E&M" localization method added. To be published MPL
Gravitating global monopoles in extra dimensions and the brane world concept
Multidimensional configurations with Minkowski external space-time and a
spherical global monopole in extra dimensions are discussed in the context of
the brane world concept. The monopole is formed with a hedgehog-like set of
scalar fields \phi^i with a symmetry-breaking potential V depending on the
magnitude \phi^2 = \phi^i \phi^i. All possible kinds of globally regular
configurations are singled out without specifying the shape of V(\phi). These
variants are governed by the maximum value \phi_m of the scalar field,
characterizing the energy scale of symmetry breaking. If \phi_m < \phi_cr
(where \phi_cr is a critical value of \phi related to the multidimensional
Planck scale), the monopole reaches infinite radii while in the ``strong field
regime'', when \phi_m\geq \phi_cr, the monopole may end with a cylinder of
finite radius or possess two regular centers. The warp factors of monopoles
with both infinite and finite radii may either exponentially grow or tend to
finite constant values far from the center. All such configurations are shown
to be able to trap test scalar matter, in striking contrast to RS2 type 5D
models. The monopole structures obtained analytically are also found
numerically for the Mexican hat potential with an additional parameter acting
as a cosmological constant.Comment: 21 pages, 6 figures, latex, gc styl
Brane world corrections to Newton's law
We discuss possible variations of the effective gravitational constant with
length scale, predicted by most of alternative theories of gravity and unified
models of physical interactions. After a brief general exposition, we review in
more detail the predicted corrections to Newton's law of gravity in diverse
brane world models. We consider various configurations in 5 dimensions (flat,
de Sitter and AdS branes in Einstein and Einstein-Gauss-Bonnet theories, with
and without induced gravity and possible incomplete graviton localization), 5D
multi-brane systems and some models in higher dimensions. A common feature of
all models considered is the existence of corrections to Newton's law at small
radii comparable with the bulk characteristic length: at such radii, gravity on
the brane becomes effectively multidimensional. Many models contain superlight
perturbation modes, which modify gravity at large scale and may be important
for astrophysics and cosmology.Comment: Brief review, 16 pages, 92 references. Some description and
references adde