The Hubble constant and the deceleration parameter in anisotropic cosmological spaces of Petrov type D

Marín, Alvarado; Eduardo, Rodrigo

doi:10.12988/astp.2016.6930

Cited by 5 publications

(5 citation statements)

References 10 publications

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“…Using either of the above relations, we obtain q = 2 for the present model. This is the same value of deceleration parameter as obtained for Petrov Type-D anisotropic cosmological solutions by Alvarado [56] and, in the case of an anisotropic dark energy cosmological model, under the framework of a generalised Brans-Dicke theory by Tripathy et al [57].…”

Section: Ks Modelsupporting

confidence: 83%

Anisotropic Universes Sourced by Modified Chaplygin Gas

Ray,

Tripathy,

Sengupta

et al. 2023

Universe

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In this work, we perform a comparative study of the Kantowski–Sachs (KS) and Bianchi-I anisotropic universes with Modified Chaplygin gas (MCG) as matter source. We obtain the volume and scale factors as solutions to the Einstein Field Equations (EFEs) for the anisotropic universes, and check whether the initial anisotropy is washed out or not for different values of the MCG parameters present in the solution by obtaining the anisotropy parameters for each solution. The deceleration parameter is also obtained for each solution, the significance of which is discussed in the concluding section. Interestingly there are a number of notable results that appear from our study which help us to compare and contrast the two different anisotropic models along with proper understanding of the role of MCG as matter source in these models.

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Section: Ks Modelsupporting

confidence: 83%

Anisotropic Universes Sourced by Modified Chaplygin Gas

Ray,

Tripathy,

Sengupta

et al. 2023

Universe

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“…Both solutions tend to the spatial isotropic regime equivalent to the dark energy model for a flat model of FRWL with time, and tend to be equivalent to those obtained for a model of dust, with small time. Both the Hubble and the deceleration parameter depend on time, which marks a fundamental difference between the same parameters obtained for the flat universe of FRWL, or the solution of the Kasner vacuum [15], where the deceleration parameter is constant for each type of model or for all of them in Kasner's case. In the resulting solutions, the parameters are time dependent, so in certain limits they behave as the analogous obtained from the Kasner solution and from other limits, as the analogous to the FRWL solution of the flat model of dark energy, it exists a transitional path between them through time, so that the parameter q changes its value and sign, which means that a period of deceleration is presented in small values t, and then it changes to a process of acceleration as time passes.…”

Section: Resultsmentioning

confidence: 92%

“…when t → ∞. The deceleration parameter q is defined as in [15], with the pattern q = − 1 +Ḣ H 2 √ g 00 = − 1 + 1 3…”

mentioning

confidence: 99%

Exact solutions of a Chaplygin gas in an anisotropic space-time of Petrov D

Alvarado¹

2017

astp

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This document obtains two exact solutions to the anisotropic spacetime of Petrov D by using the model of a perfect fluid. These solutions represent a scenario of a universe in which the pressure P and the energetic density µ of the fluid are inversely proportional (Chaplygin's type P = −Q 2 /µ), where Q is a constant of proportionality. It is established that the symmetry of those models, in the proximities when t → 0, is equivalent to the analogues for the dust model, and might tend to behave as the solutions of the flat or vacuum LRS Kasner solution (Local Rotational Symmetry). Although the solutions are not flat or vacuum in any of the cases, in those proximities, the density tends to infinite and with no pressure. When t → ∞, the models tend to behave as the isotropic flat model of the type FRWL. In the analysis of the Hubble and the deceleration parameters obtained that in those solutions, the Hubble's constant and the deceleration parameter, depend on time and manner in which their values, or tendency, significantly evolve. The deceleration parameter q changes its sign as times passes, so that it represents an initial deceleration process that, in continuity, constantly changes to a process of acceleration.

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“…The Hubble parameters H and deceleration q, for the anisotropic symmetry of the type of Petrov D, have been studied in [18] and are defined, for a symmetry of the type…”

Section: The Hubble Parameters and Deceleration Imentioning

confidence: 99%

Exact cosmological solutions of isobaric scalar fields in space-times: anisotropic of the type of Petrov D and isotropic homogeneous

Alvarado¹

2018

astp

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In this paper two exact solutions to the Einstein equations are obtained, from a isobaric scalar field (P = const). It is established that the solution of this field in a symmetry of the type of Petrov D, tends with the increasing time, to become isotropic, so that it agrees with the solution of an isobaric scalar field, but in homogeneous isotropic symmetry (of the type Friedmann flat). It is determined that in the outskirts of the cosmological singularity, the solutions of both symmetries are unique, but as time increases, they tend to be close to the dark energy solutions in FRWL plane. The homogeneous anisotropic solution of Petrov D is divided into two possible solutions, depending if a constant is positive or not, for the case in which the constant is positive, it is had that space-time, in its beginnings, expands in mayor form on one of its axes (axis z), tending to a solution of Kasner's vacuum when t → 0, but if the constant is taken as negative, the expansion becomes more intense on a plane (plane xy) in relation with the axis z. If it is considerate the constant as negative, when t → 0, the solution resembles that of the flat world, but without it being so. There are studied the Hubble parameters and the deceleration in both solutions, and it is determined that the Hubble parameter, tends an infinity, when t → 0 and to a proportional constant to |P |, when t → ∞, in the solutions of both symmetries. The deceleration parameter, at the beginning of these symmetries, has a positive value (different for each model), and with the 320 R. Alvarado course of time it changes to negative, so that in the above mentioned models, the expansion begins with a deceleration process, decreasing until a time in which it stops decelerating and from this, begins an acceleration process, which tends to become constant with the increase of the time. The stability of Jacobi is studied and it is obtained that the solution with the homogeneous anisotropic symmetry of Petrov D, is stable, for t > 0, and for the case of homogeneous isotropic space-time solution, it is for a certain interval of time t ∈]0, t 1/2 ], in where t 1/2 is approximately half of the time of existence that is considered it has the Universe.

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The Hubble constant and the deceleration parameter in anisotropic cosmological spaces of Petrov type D

Cited by 5 publications

References 10 publications

Anisotropic Universes Sourced by Modified Chaplygin Gas

Anisotropic Universes Sourced by Modified Chaplygin Gas

Exact solutions of a Chaplygin gas in an anisotropic space-time of Petrov D

Exact cosmological solutions of isobaric scalar fields in space-times: anisotropic of the type of Petrov D and isotropic homogeneous

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