227 research outputs found
Sp-brane accelerating cosmologies
We investigate time dependent solutions (S-brane solutions) for product
manifolds consisting of factor spaces where only one of them is non-Ricci-flat.
Our model contains minimally coupled free scalar field as a matter source. We
discuss a possibility of generating late time acceleration of the Universe. The
analysis is performed in conformally related Brans-Dicke and Einstein frames.
Dynamical behavior of our Universe is described by its scale factor. Since the
scale factors of our Universe are described by different variables in both
frames, they can have different dynamics.
Indeed, we show that with our S-brane ansatz in the Brans-Dicke frame the
stages of accelerating expansion exist for all types of the external space
(flat, spherical and hyperbolic). However, applying the same ansatz for the
metric in the Einstein frame, we find that a model with flat external space and
hyperbolic compactification of the internal space is the only one with the
stage of the accelerating expansion. Scalar field can prevent this
acceleration. It is shown that the case of hyperbolic external space in
Brans-Dicke frame is the only model which can satisfy experimental bounds for
the fine structure constant variations. We obtain a class of models where a
pare of dynamical internal spaces have fixed total volume. It results in fixed
fine structure constant. However, these models are unstable and external space
is non-accelerating.Comment: 17 pages, 4 figures, accepted in PR
Cosmology with two compactification scales
We consider a (4+d)-dimensional spacetime broken up into a (4-n)-dimensional
Minkowski spacetime (where n goes from 1 to 3) and a compact (n+d)-dimensional
manifold. At the present time the n compactification radii are of the order of
the Universe size, while the other d compactification radii are of the order of
the Planck length.Comment: 16 pages, Latex2e, 7 figure
Integrable Multicomponent Perfect Fluid Multidimensional Cosmology II: Scalar Fields
We consider anisotropic cosmological models with an universe of dimension 4
or more, factorized into n>1 Ricci-flat spaces, containing an m-component
perfect fluid of m non-interacting homogeneous minimally coupled scalar fields
under special conditions. We describe the dynamics of the universe: It has a
Kasner-like behaviour near the singularity and isotropizes during the expansion
to infinity.
Some of the considered models are integrable, and classical as well as
quantum solutions are found. Some solutions produce inflation from "nothing".
There exist classical asymptotically anti-de Sitter wormholes, and quantum
wormholes with discrete spectrum.Comment: 28 pages, LaTeX, subm. to Gen. Rel. Gra
Multidimensional Classical and Quantum Wormholes in Models with Cosmological Constant
A multidimensional cosmological model with space-time consisting of Einstein spaces is investigated in the presence of a cosmological
constant and a homogeneous minimally coupled scalar field
as a matter source. Classical and quantum wormhole solutions are
obtained for and all being Ricci-flat. Classical wormhole
solutions are also found for and only one of the being
Ricci-flat for the case of spontaneous compactification of the internal
dimensions with fine tuning of parameters.Comment: 31 pages, 5 figures available on request from [email protected], LaTeX,
Potsdam University, preprint AIP 94-0
Cosmological solutions in multidimensional model with multiple exponential potential
A family of cosmological solutions with Ricci-flat spaces in the
theory with several scalar fields and multiple exponential potential is
obtained when coupling vectors in exponents obey certain relations. Two
subclasses of solutions with power-law and exponential behaviour of scale
factors are singled out. It is proved that power-law solutions may take place
only when coupling vectors are linearly independent and exponential dependence
occurs for linearly dependent set of coupling vectors. A subfamily of solutions
with accelerated expansion is singled out. A generalized isotropization
behaviours of certain classes of general solutions are found. In quantum case
exact solutions to Wheeler-DeWitt equation are obtained and special "ground
state" wave functions are considered.Comment: 22 pages, 1 figur
Non-commutative multi-dimensional cosmology
A non-commutative multi-dimensional cosmological model is introduced and used
to address the issues of compactification and stabilization of extra dimensions
and the cosmological constant problem. We show that in such a scenario these
problems find natural solutions in a universe described by an increasing time
parameter.Comment: 9 pages, 1 figure, to appear in JHE
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