51 research outputs found
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
Noncommutativity in Effective Loop Quantum Cosmology
We construct a noncommutative extension of the Loop Quantum Cosmology
effective scheme for the open FLRW model with a free scalar field via a theta
deformation. Firstly, a deformation is implemented in the configuration sector,
among the holonomy variable and the matter degree of freedom. We show that this
type of noncommutativity retain, to some degree, key features of the Loop
Quantum Cosmology paradigm for a free field. Secondly, a deformation is
implemented in the momentum sector, among the momentum associated to the
holonomy variable and the momentum associated to the matter field. We show that
in this latter case the scalar field energy density is bounded and has the same
maximum as in standard Loop Quantum Cosmology, signaling a higher degree of
compatibility
Noncommutative effective LQC: A (pre-)inflationary dynamics investigation
We conduct a (pre-)inflationary dynamics study within the framework of a
simple noncommutative extension of effective loop quantum cosmology -- put
forward recently by the authors -- which preserves its key features (in
particular, the quantum bounce is maintained). A thorough investigation shows
that the (pre-)inflationary scenario associated to the chaotic quadratic
potential is in the overall the same as the one featured in standard loop
quantum cosmology (which reinforces the conclusion reached by the authors in a
preliminary analysis). Hence, this (pre-)inflationary scenario does not easily
distinguish between standard loop quantum cosmology and the aforementioned
noncommutative scheme. It is argued that a particular tuning of the
noncommutativity parameter could accommodate for subtle effects at the level of
primordial perturbations (the hybrid quantization framework being a tentative
route of analysis).Comment: 22 pages, 18 figures, 1 tabl
- …