Anisotropic Cosmological Models Research Articles

Anisotropic Cosmological Model with SQM in f(R, Lm) Gravity

A locally rotationally symmetric Bianchi-I model filled with strange quark matter (SQM) is explored in f(R, Lm) gravity as a non-linear functional of the form f(R, Lm)=R/2 +Lαm, where α is the free model parameter. We considered the special law of variation of Hubble’s parameter proposed by Berman (1983) and also used the power law relation between the scale factors to obtain the exact solution of the field equation, which matches the model of the universe. We also analyze the physical and geometrical aspects of the universe’s kinematic and dynamic behavior. Additionally, we employ equation-of-state (EoS) parameters and statefinder parameters as analytical tools to gain insights into the evolution of the universe. We use the ΛCDM model as a benchmark to validate the results. By placing the deviations of the universe from ΛCDM model and yet making important contributions to the study of the anisotropic nature of f(R, Lm) gravity within the framework of cosmological dynamics, the paper increases our comprehension of our cosmic evolution.

Cosmic Evolution in a Bianchi type-V Universe with Barrow Holographic Dark Energy with Granda-Oliveros Length Scale as IR Cutoff

In this work, we construct a spatially homogeneous and anisotropic Bianchi type-V cosmological model with a hybrid expansion law by considering the universe to be filled with cold dark matter and non-interacting Barrow holographic dark energy with Granda-Oliveros length scale as IR cutoff. The physical and kinematical characteristics of the resulting model are discussed by studying the evolution of various parameters of cosmological importance such as the Hubble parameter, the deceleration parameter, the anisotropic parameter, the equation of state parameter, jerk parameter etc. We also examine whether the energy conditions are satisfied or violated. Our analysis reveals that the Null,Weak, and Dominant energy conditions are fullfilled, while the Strong Energy Condition is violated, which supports the accelerated expansion of the universe. Statefinder diagnostics have also been performed based on recent cosmological observations in order to compare our model with different dark energy cosmological scenario. Additionally, we establish the correspondence between the quintessence scalar field and the Barrow holographic dark energy model, supporting our description of the universe’s accelerated expansion.

Anisotropic cosmological models in f(T) theory of gravity with mixture of fluids

Anisotropic cosmological models in f(T) theory of gravity with mixture of fluids

(4+1)-D homogeneous anisotropic string cosmological models with dilaton and anti-symmetric matter

(4+1)-D homogeneous anisotropic string cosmological models with dilaton and anti-symmetric matter

Bouncing behavior of anisotropic cosmological model

We study locally rotationally symmetric (LRS) Bianchi type-I cosmological model in the presence of general theory of relativity. The source for energy–momentum tensor is assumed a perfect fluid. The field equations have been solved by using special form of the average scale factor [Formula: see text], where [Formula: see text] is initial cosmic time and [Formula: see text] is constant, proposed by Cai et al. [J. High Energy Phys. 710, 071 (2007)]. The physical properties and bouncing behavior of the model are discussed through graphical representation. The violation of strong energy condition (SEC) further supports the behavior of accelerated expansion of the Universe. The stability analysis of the model is discussed through geometrical representation.

Nonmetric geometric flows and quasicrystalline topological phases for dark energy and dark matter in f(Q)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(Q)$$\\end{document} cosmology

We elaborate on nonmetric geometric flow theory and metric-affine gravity with applications in modern cosmology. Two main motivations for our research follow from the facts that (1) cosmological models for f(Q) modified gravity theories, MGTs, are efficient for describing recent observational data provided by the James Webb Space Telescope; and (2) the statistical thermodynamic properties of such nonmetric locally anisotropic cosmological models can be studied using generalizations of the concept of G. Perelman entropy. We derive nonmetric distorted R. Hamilton and Ricci soliton equations in such canonical nonholonomic variables when corresponding systems of nonlinear PDEs can be decoupled and integrated in general off-diagonal forms. This is possible if we develop and apply the anholonomic frame and connection deformation method involving corresponding types of generating functions and generating sources encoding nonmetric distortions. Using such generic off-diagonal solutions (when the coefficients of metrics and connections may depend generically on all spacetime coordinates), we model accelerating cosmological scenarios with quasi-periodic gravitational and (effective) matter fields; and study topological and nonlinear geometric properties of respective dark energy and dark matter, DE and DM, models. As explicit examples, we analyze some classes of nonlinear symmetries defining topological quasicrystal, QC, phases which can modified to generate other types of quasi-periodic and locally anisotropic structures. The conditions when such nonlinear systems possess a behaviour which is similar to that of the Lambda cold dark matter (Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM) scenario are stated. We conclude that nonmetric geometric and cosmological flows can be considered as an alternative to the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM concordance models and speculate on how such theories can be elaborated. This is a partner work with generalizations and applications of the results published by Bubuianu, Vacaru et all. EPJC 84 (2024) 211; 80 (2020) 639; 78 (2018) 393; 78 (2018) 969; and CQG 35 (2018) 245009.

Hubble diagrams in statistically homogeneous, anisotropic universes

We consider the form of Hubble diagrams that would be constructed by observers in universes that are homogeneous but anisotropic, when averaged over suitably large length-scales. This is achieved by ray-tracing in different directions on the sky in families of exact inhomogeneous cosmological solutions of Einstein's equations, in order to determine the redshifts and luminosity distances that observers in these space-times would infer for distant astrophysical objects. We compare the results of this procedure to the Hubble diagrams that would be obtained by direct use of the large-scale-averaged anisotropic cosmological models, and find that observables calculated in the averaged model closely agree with those obtained from ray-tracing in all cases where a statistical homogeneity scale exists. In contrast, we find that in cosmologies with spaces that contain no statistical homogeneity scale that Hubble diagrams inferred from the averaged cosmological model can differ considerably from those that observers in the space-time would actually construct. We hope that these results will be of use for understanding and interpreting recent observations that suggest that large-scale anisotropy may have developed in the late Universe.

Anisotropy Bianchi Type-III Cosmological Model in Brans-Dicke Theory of Gravitation

Objectives: To derive the multi-fluid anisotropic Bianchi type-III cosmological model filled with radiation and matter in the presence of Brans-Dicke scalar-tensor theory. Method: In this paper, we have calculated Brans-Dicke field equations in anisotropic Bianchi type -III space times in the presence of matter and radiation which are minimally interacting fields. To obtain the determinate solution of the model, we considered i) the state of the equation , ii) the shear scalar is directly proportional to the expansion scalar i.e., . Also, consider the deceleration parameter, , where with which yields models with constant deceleration parameter. Findings: This solution shows an anisotropic radiation model in Brans-Dicke's theory. Also, it shows accelerated expansion of the universe and transition of the universe from the deceleration phase to the accelerated phase. Novelty: The derived model's many parameters support recent cosmological findings, indicating the model's good discovery. Thus, within the framework of our established model, we are able to comprehend the cosmic development. Keywords: Bianchi type-III, Brans-Dicke theory, Multifluid, Deceleration parameter, Λ CDM

Kinematic parameters and Raychaudhuri equation in the Kantowski-Sachs model

In this work we present a review of the calculations of homogeneous and anisotropic cosmological models, particularly the Kantowski-Sachs cosmological model. As an innovative contribution, we calculate an exact solution to the field equations with a general expression for the material content of the Universe. We obtain the expressions for energy density in this general case. We also study the case involving a scalar field. We investigate the evolution dynamics of the model, encompassing the Hubble, density, and deceleration parameters. We calculate the kinematic parameters associated with the model, namely: the scalar expansion Θ, the shear scalar σ, the rotation parameter ω and the parameter R α β U α U β , also known as Raychaudhuri scalar or convergence condition, all these parameters expressed in the Raychaudhuri equation.

Anisotropic Bianchi Type-1 Cosmological Model Containing Dark Energy

Considering the LRS Bianchi type I metric here we studied the spatial homogeneous and anisotropic dark energy cosmological models in the frame work of B-D scalar tensor theory of gravity along with variable equation of parameter and deceleration parameter. Exact solutions of field equations are obtained with certain physical assumptions in different cases. The physical behavior of the model is also discussed in details.

A Study on Cosmological Model of Anisotropic Universe with Electromagnetic Field and Cloud Strings in the Frame Work of General Relativity

In this study, we have investigated the Bianchi type-III anisotropic cosmological model in the presence of cloud strings with the electromagnetic field in the general theory of relativity. Exact solutions of field equations are obtained using the fact that shear scalar is proportional to scalar expansion and constant decelerating parameter, which is derived from the variation law of Hubble parameter proposed by Berman(Nuovo Cimento B 74, 182 (1983))and linearly varying decelerating parameter proposed by Akarsu and Dereli(International Journal of Theoretical Physics, 51,612(2012)). The dynamics and significance of the physical parameters of the model are discussed using a graphical representation of these parameters. The dynamics and significance of the physical parameters of the models are discussed.

An anisotropic cosmological model with Bianchi type III universe in f(G) gravity

The paper is devoted to exploring the exact solution of the modified Einstein's field in the setting of spatially homogeneous and anisotropic Bianchi type III spacetime in modified f(G) gravity, where G is Gauss-Bonnet invariant. Here, by employing the hyperbolic hybrid scale factor a = emt (sinh(t))n in which m,n are positive constants, with the power-law f (G)=βGm+1 model where β,m are arbitrary constants, we computed the physical and geometrical properties of the cosmological parameters of the model. The results of the model parameters are well satisfied with recent cosmological observational data. To get the exact solution of the field equation of the Bianchi type III model in the presence of an anisotropic dark fluid, we consider the relation in which the shear scalar (σ) is proportional to the expansion scalar (θ), resulting in C = An. Furthermore, the energy conditions for the power-law f(G) model are graphically examined, and it turns out that the null energy condition (NEC), weak energy condition (WEC), and dominant energy condition (DEC) are well satisfied except for the strong energy condition (SEC). The violation of the strong energy conditions (SEC) indicates the f(G) model supports the universe's current expansion with negative pressure, having a quintessence model in the present and Λ cold dark matter (CDM) model in the future.

Anisotropic Bianchi Type VI<sub>0</sub> Cosmological Models in a Modified <i>f</i>(<i>R,T</i>) Gravity

We investigate the spatially homogeneous and anisotropic Bianchi type VI0 cosmological models with modified Holographic Ricci Dark Energy subjected to f(R,T) gravity. We have obtained the solution of the field equations with the help of the power law relation among the scale factors. Dynamical parameters are calculated by using the connection between pressure and energy density. The kinematical implications of the models are also examined. Graphical presentation of different cosmological parameters is shown for distinct values of the parameter of the model

Anisotropic Fractional Cosmology: K-Essence Theory

In the particular configuration of the scalar field k-essence in the Wheeler–DeWitt quantum equation, for some age in the Bianchi type I anisotropic cosmological model, a fractional differential equation for the scalar field arises naturally. The order of the fractional differential equation is β=2α2α−1. This fractional equation belongs to different intervals depending on the value of the barotropic parameter; when ωX∈[0,1], the order belongs to the interval 1≤β≤2, and when ωX∈[−1,0), the order belongs to the interval 0<β≤1. In the quantum scheme, we introduce the factor ordering problem in the variables (Ω,ϕ) and its corresponding momenta (ΠΩ,Πϕ), obtaining a linear fractional differential equation with variable coefficients in the scalar field equation, then the solution is found using a fractional power series expansion. The corresponding quantum solutions are also given. We found the classical solution in the usual gauge N obtained in the Hamiltonian formalism and without a gauge. In the last case, the general solution is presented in a transformed time T(τ); however, in the dust era we found a closed solution in the gauge time τ.

Observational constraints on anisotropic cosmological model in Lyra’s manifold

In the present study, we have explored an axially symmetric Bianchi I universe with Lyra’s geometry. We assumed variable displacement vector as component of Lyra’s geometry in the Einstein’s field equations. We developed and presented exact solutions of the field equations of proposed model. The parameters of model have been extracted using latest observational finding of OHD, Pantheon and BAO data sets. The best fit values are estimated using MCMC method. Features like deceleration parameter, particle horizon, age of universe and jerk parameter are explored. Further Om and statefinder diagnosis of the assumed model are also discussed for geometrical comparison with the standard ΛCDM model.

Cloud String Cosmological Models Using Different Decelerating Parameters with Electromagnetic Field in General Theory of Relativity

In this study, we have investigated the Bianchi type-III anisotropic cosmological model in the presence of cloud strings with electro- magnetic field in general theory of relativity. Exact solutions of field equations are obtained using the fact that shear scalar is proportional to scalar expansion and constant decelerating parameter which is derived from variation law of Hubble parameter proposed by Berman[1] and linearly varying decelerating parameter proposed by Akarsu and Dereli [2]. The dynamics and significance of physical parameters of the model are discussed using a graphical representation of these parameters.The dynamics and significance of physical parameters of the models are discussed.

Is the Universe Anisotropic Right Now? Comparing the Real Universe with the Kasner’s Space-Time

We investigate possible astronomical manifestations of space-time anisotropy. The homogeneous vacuum Kasner solution was chosen as a reference anisotropic cosmological model because there are no effects caused by inhomogeneity in this simple model with a constant degree of anisotropy. This anisotropy cannot become weak. The study of its geodesic structure made it possible to clarify the properties of this space-time. It showed that the degree of manifestation of anisotropy varies significantly depending on the travel time of the light from the observed object. For nearby objects, for which it does not exceed half the age of the universe, the manifestations of anisotropy are very small. Distant objects show more pronounced manifestations; for example, in the distribution of objects over the sky and over photometric distances. These effects for each of the individual objects decrease with time but, in general, the manifestations of anisotropy in the Kasner space-time remain constant due to the fact that new sources come from beyond the cosmological horizon. We analyze observable signatures of the Kasner-type anisotropy and compare it to observations. These effects were not found in astronomical observations, including the study of the CMB. We can assume that the Universe has always been isotropic or almost isotropic since the recombination era. This does not exclude the possibility of its significant anisotropy at the moment of the Big Bang followed by rapid isotropization during the inflationary epoch.

Anisotropic Cosmological Model in f (R,T) Theory of Gravity with a Quadratic Function of T

In this paper, we study spatially homogeneous and anisotropic Bianchi type-I space-time filled with perfect fluid within the framework of f(R,T) theory of gravity for the functional form f(R,T)=R+2f(T) with f(T)=αT+βT2, where α and β are constants. Exact solutions of the gravitational field equations are obtained by assuming the average scale factor to obey a hybrid expansion law and some cosmological parameters of the model are derived. Two special cases, leading to the power-law expansion and the exponential expansion, are also considered. We investigate the physical and geometrical properties of the models by studying the evolution graphs of some relevant cosmological parameters such as the Hubble parameter (H), the deceleration parameter ( q) etc.

Anisotropic Cosmology in the Local Limit of Nonlocal Gravity

Within the framework of the local limit of nonlocal gravity (NLG), we investigate a class of Bianchi type I spatially homogeneous but anisotropic cosmological models. The modified field equations are presented in this case, and some special solutions are discussed in detail. This modified gravity theory contains a susceptibility function S(x) such that general relativity (GR) is recovered for S = 0. In the modified anisotropic cosmological models, we explore the contribution of S(t) and its temporal derivative to the local anisotropic cosmic acceleration. The implications of our results for observational cosmology are briefly discussed.

Bianchi type-III holographic dark energy cosmological model in [formula omitted] theory of gravitation

In this paper, we have studied the spatially homogeneous and anisotropic Bianchi type-III cosmological model in the presence of pressureless matter and Holographic dark energy within the framework of f(R,T) gravity. We have constructed a cosmological model with an appropriate choice of function f(T). Field equations are solved using the relation between the metric potentials A=Cn and using a simple power-law form of a metric potential C=tn. The main objective behind this paper is to explore some physically significant discussions on the evolution of the universe. It is observed that the Hubble parameter H, scalar expansion θ and shear scalar σ diverge at the initial epoch while they approach zero for a large value of time and the anisotropic parameter Am is constant. The negative value of the deceleration parameter indicates the present acceleration of the universe.