269 research outputs found
Time-dependent toroidal compactification proposals and the Bianchi type I model: classical and quantum solutions
In this work we construct an effective four-dimensional model by
compactifying a ten-dimensional theory of gravity coupled with a real scalar
dilaton field on a time-dependent torus. This approach is applied to
anisotropic cosmological Bianchi type I model for which we study the classical
coupling of the anisotropic scale factors with the two real scalar moduli
produced by the compactification process. Under this approach, we present an
isotropization mechanism for the Bianchi I cosmological model through the
analysis of the ratio between the anisotropic parameters and the volume of the
Universe which in general keeps constant or runs into zero for late times. We
also find that the presence of extra dimensions in this model can accelerate
the isotropization process depending on the momenta moduli values. Finally, we
present some solutions to the corresponding Wheeler-DeWitt (WDW) equation in
the context of Standard Quantum Cosmology.Comment: LaTeX source, 16 pages, Modified title and additional references.
Advances in High Energy Physics, 201
Classical solutions in five dimensional induced matter theory and its relation to an imperfect fluid
We study five dimensional cosmological models with four dimensional
hypersufaces of the Bianchi type I and V. In this way the five dimensional
vacuum field equations , led us to four dimensional matter
equations and the matter is interpreted as a purely
geometrical property of a fifth dimension. Also, we find that the
energy-momentum tensor induced from the fifth dimension has the structure of an
imperfect fluid that has dissipative terms.Comment: 16 pages, latex, no figure
Classical Bianchi type I cosmology in K-essence theory
We use one of the simplest forms of the K-essence theory and we apply it to
the classical anisotropic Bianchi type I cosmological model, with a barotropic
perfect fluid modeling the usual matter content and with cosmological constant.
The classical solutions for any but the stiff fluid and without cosmological
constant are found in closed form, using a time transformation. We also present
the solution whith cosmological constant and some particular values of the
barotropic parameter. We present the possible isotropization of the
cosmological model, using the ratio between the anisotropic parameters and the
volume of the universe and show that this tend to a constant or to zero for
different cases. We include also a qualitative analysis of the analog of the
Friedmann equation.Comment: 15 pages with one figure, accepted in Advances in High Energy Physic
Cosmological Bianchi Class A models in S\'aez-Ballester theory
We use the S\'aez-Ballester (SB) theory on anisotropic Bianchi Class A
cosmological model, with barotropic fluid and cosmological constant, using the
Hamilton or Hamilton-Jacobi approach. Contrary to claims in the specialized
literature, it is shown that the S\'aez-Ballester theory cannot provide a
realistic solution to the dark matter problem of Cosmology for the dust epoch,
without a fine tunning because the contribution of the scalar field in this
theory is equivalent to a stiff fluid (as can be seen from the energy--momentum
tensor for the scalar field), that evolves in a different way as the dust
component. To have similar contributions of the scalar component and the dust
component implies that their past values were fine tunned. So, we
reinterpreting this null result as an indication that dark matter plays a
central role in the formation of structures and galaxy evolution, having
measureable effects in the cosmic microwave bound radiation, and than this
formalism yield to this epoch as primigenius results. We do the mention that
this formalism was used recently in the so called K-essence theory applied to
dark energy problem, in place to the dark matter problem. Also, we include a
quantization procedure of the theory which can be simplified by reinterpreting
the theory in the Einstein frame, where the scalar field can be interpreted as
part of the matter content of the theory, and exact solutions to the
Wheeler-DeWitt equation are found, employing the Bianchi Class A cosmological
models.Comment: 24 pages; ISBN: 978-953-307-626-3, InTec
Cosmologies with scalar fields from higher dimensions applied to Bianchi type model: classical and quantum solutions
In this work we construct an effective four-dimensional model by
compactifying a ten-dimensional theory of gravity coupled with a real scalar
dilaton field on a time-dependent torus. The corresponding action in four
dimensions is similar to the action of K-essence theories. This approach is
applied to anisotropic cosmological Bianchi type model for which
we study the classical coupling of the anisotropic scale factors with the two
real scalar moduli produced by the compactification process. The classical
Einstein field equations give us a hidden symmetry, corresponding to equal
radii B=C, which permits us to solve exactly the equations of motion. With this
hidden symmetry, then we solve the FRW, finding that the scale factor goes to B
radii. Also the corresponding Wheeler-DeWitt (WDW) equation in the context of
Standard Quantum Cosmology is solved. Bohm's formalism for this cosmological
model is revisited too.Comment: 13 pages, 1 figur
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