FRW Cosmological Model Research Articles

Cosmological implications on two fluids model universe with parametrization of Hubble parameter in Lyra manifold

In this research, we explore the cosmological implication on five-dimensional FRW cosmological model for k = 0 in presence of two perfect fluids: ordinary baryonic fluid and an interacting dark energy in the context of Lyra’s manifold. We obtain an exact solution of the field equations by assuming the parametrization of the Hubble parameter H(a) = τ(1 + a −ν ), where a is a scale factor and τ > 0, ν > 1 are the arbitrary constants. This results in a universe model with a transition from a previously decelerating universe to the current accelerating universe, characterized by a time-dependent deceleration parameter. Moreover, we have used 46 observational Hubble data sets to restrict the parameters of our suggested model. Some cosmological parameters have been examined about the nature of the proposed model universe. It is shown that our model can be considered a realistic one.

A comprehensive analysis of observational cosmology in [formula omitted] gravity with deep learning and MCMC method

Our goal in this study is to build FRW cosmological models inside the f(Q) theory of gravity framework by using Bayesian statistics and deep learning method. We investigate the universe’s accelerating behaviour for a specific version of the f(Q) gravity model using a novel, straightforward parameterization of the Hubble parameter in the form H=H0(1+z)1+q0−q1exp(q1z). The corresponding free parameters in H(z) are limited between 1σ and 2σ confidence bounds using the χ2-minimization procedure. The results show that all the numbers we got are in the ballpark of what cosmological observations would predict. In our model, we examined the physical behaviour of the cosmos using characteristics such as energy density, pressure, and equation of state. We analysed kinematic factors including Hubble parameter, acceleration parameter, and universe age in our model. In our concept, the deceleration parameter q(z) represents the universe’s transition from deceleration to acceleration. We employ a novel approach for parameter estimation by utilizing a mixed neural network (MNN) that combines artificial neural networks (ANN) and mixture density networks (MDN). This new methodology leverages the strengths of ANN, MDN, and MNN to enhance the accuracy of parameter estimation.

Two forms of dark energy in fractal cosmological model using specific Hubble parameter

The main objective of this article is to study the fractal FRW cosmological model consisting two forms of dark energy. We studied behavior of the universe in a fractal framework using dark energy accommodated in our universe. The solution of field equations are obtained by using Hubble parameter for transit scale factor H(z)=ϵa−δ+λ . We have obtained the best fitting values of the model parameters ϵ,δ and λ by constraining our model with latest Hubble and SNe-Ia data sets . Finally we perform state-finder diagnosis and observe that obtained model close to standard ΛCDM model.

Conharmonically Flat Spacetimes in FRW Cosmological Model

Conharmonically Flat Spacetimes in FRW Cosmological Model

CERTAIN COSMOLOGICAL MODELS WITH VARIATION OF HUBBLE PARAMETER

The present paper deals with the FRW-Cosmological Model of universe for W2 flat perfect fluid space time. Einstein field equations with variable cosmological constant (Λ) has been obtained for such spacetime and in order to get the complete cosmological solution the law of variation for Hubble’s parameter is considered. A new class of solution have been discussed for the Einstein field equations with variable cosmological constant in which the pressure, energy density, and cosmological constant Λ are found to be decreasing function of cosmic time. The physical and kinematical properties of models are also discussed.

Gravitational wave memory and its tail in cosmology

We study gravitational wave memory effect in the FRW cosmological model with matter and cosmological constant. Since the background is curved, gravitational radiation develops a tail part arriving after the main signal that travels along the past light cone of the observer. First we discuss first order gravitational wave sourced by a binary system, and find that the tail only gives a negligible memory, in accord with previous results. Then we study the nonlinear memory effect coming from induced gravitational radiation sourced by first order gravitational radiation propagating over cosmological distances. In the light cone part of the induced gravitational wave we find a novel term missed in previous studies of the cosmological memory effect. Furthermore, we show that the induced gravitational wave has a tail part that slowly accumulates after the light cone part has passed and grows to a sizeable magnitude over a cosmological timescale. This tail part of the memory effect will be a new component in the stochastic gravitational wave background.

Accelerated Universe from Modified Chaplygin Gas and Tachyonic Fluid

A cosmological model with an exotic fluid is investigated. We show that the equation of state of this “modified Chaplygin” gas can describe the current accelerated expansion of the universe. We then reexpress it as FRW cosmological model containing a scalar field ϕ and find its self-interacting potential. Moreover motivated by recent works on tachyon field theory, a map for this exotic fluid as a normal scalar field ϕ with Lagrangian Lϕ=ϕ˙22−U(ϕ) to the tachyonic field T with Lagrangian LT=−V(T)1−T˙2 is obtained.

FRW cosmological models with Barrow holographic dark energy in Brans–Dicke theory

In this paper, we have generalized the behaviors of transit cosmological model under the observational data with Barrow holographic dark energy. We consider the scale factor field as [Formula: see text] to get exact solutions for the field equations in a non-flat FRW universe in Brans–Dicke theory. The values of the model parameters [Formula: see text] and [Formula: see text] are obtained by best fitting of 46 observational Hubble data (OHD) points in the range [Formula: see text]. The derived model exhibits a transition scenario for open, flat and closed universe. The EoS parameter shows a quintom-like behavior, lies both quintessence ([Formula: see text]) and phantom ([Formula: see text]) regions and crosses the phantom divide. The matter and dark energy density parameters [Formula: see text], scalar field [Formula: see text] and other cosmological parameters provide the results consistent with the recent observational datasets. Some other physical and geometrical behaviors of BHDE are also described and the satisfactory behaviors are found with current observations (OHD+JLA).

FRW cosmological models in presence of a perfect fluid within the framework of Saez-Ballester theory in five dimensional space time

In the framework of Saez-Ballester scalar-tensor theory of gravity, five-dimensional FRW space-time is considered in the presence of perfect fluid. We employed a power law between the scalar field and the universe's scale factor to get a definite solution to the field equations. Models that radiate flat, closed and open universe are shown. The model's physical features are also discussed.

Linear and center manifold analysis of FRW cosmological model with variable equation of state in Lyra geometry

The present work deals with the dynamical evolution of flat FRW cosmological model with variable equation of state in Lyra geometry. We investigate the phase-plane analysis of our constructed model. The evolution of cosmological solutions is studied by using dynamical system techniques. Stability and viability of the model are discussed using linear Jacobian stability analysis for hyperbolic equilibrium points and center manifold theory for non-hyperbolic equilibrium points.

FRW cosmological models with cosmological constant in f(R, T) theory of gravity

In the present paper, we have generalized the behaviors of the transit-decelerating to accelerating FRW cosmological model in f(R, T) gravity theory, where R and T are Ricci scalar and trace of the energy–momentum tensor, respectively. The solution of the corresponding field equations is obtained by assuming a linear function of the Hubble parameter H (i.e., q = c1 + c2H), which gives a time-dependent deceleration parameter [Formula: see text], where c3 and c2 are arbitrary integrating constants (Tiwari et al. Eur. Phys. J. Plus, 131, 447 (2016); Ibid. 132, 126 (2017)). There are two scenarios in which we explain the particular form of scale factor thus obtained: (i) by using the recent constraints from observational Hubble data (OHD) and joint light curves (JLA) data, which show a cosmic deceleration to acceleration and (ii) by using new constraints from supernovae type Ia union data, which show accelerating expansion of the universe (q < 0) throughout its evolution. We have observed that EoS parameter, energy density parameters, and important cosmological planes yield results compatible with the modern observational data. For the derived models, we have calculated various physical parameters as luminosity distance, distance modulus, and apparent magnitude versus redshift for both current supporting observations.

Transit cosmological models coupled with zero-mass scalar field with high redshift in higher derivative theory

The present study deals with a flat FRW cosmological model filled with perfect fluid coupled with the zero-mass scalar field in the higher derivative theory of gravity. We have obtained two types of universe models, the first one is the accelerating universe (power-law cosmology), and the second one is the transit phase model (hyperbolic expansion-law). We have obtained various physical and kinematic parameters and discussed them with observationally constrained values of H0. The transit redshift value is obtained zt=0.414, where the transit model shows signature-flipping and is consistent with recent observations. In our models, the present values of EoS parameter ω0 crosses the cosmological constant value ω0=−1. Also, the present age of the universe is calculated.

Compatibility between the scalar field models of tachyon, k-essence and quintessence in f(R, T) gravity

We investigate the behavior of the scalar field in f(R, T) gravity (Harko et al., Phys. Rev. D 84, 024020, 2011) inside the structure of a flat FRW cosmological model, where R and T have their usual meaning. The deterministic solution of FEs has been settled by considering the scale factor S(t)=tmekt, where m and k are positive constant. Here we utilize three ongoing imperatives (H0=73.8 and q0=−0.73) from SNe Ia Union observation (Cunha, Phys. Rev. D 79, 047301, 2009); (H0=73.8 and q0=−0.55) from Type Ia Supernova (SNIa) observation in joined with (BAO) and (CMB) observation (Giostri et al., J. Cosmol. Astropart. Phys. 03, 027, 2012); and (H0=69.2 and q0=−0.52) from (OHD+JLA) observation (Yu et al., Astrophys. J. 856, 3, 2018). We have measured and graphed several cosmological parameters and found that these findings are appropriate in comparison with the universe’s physical and kinematic properties and also compatible with ongoing observations. The correspondence between the scalar field models of tachyon, k-essence, and quintessence is investigated by us. Our model explains the potentials and the dynamics of the scalar fields in the FRW universe. The reconstructed potential is very sensible and has a scaling arrangement. Subsequently, our study supports recent observations.

Cosmological Solutions for the Geometrical Scalar-Tensor with the Potential Determined by the Noether Symmetry Approach

The aim of this work is to study a scalar-tensor theory where owing to Palatini’s variational method the space-time is endowed with a geometrical structure of Weyl integrable type. The geometrical nature of the scalar field is related to the non-metricity so that the theory is known as geometrical scalar-tensor. On the framework of Weyl transformations, a non-minimally coupled scalar-tensor theory on the Jordan frame corresponds to a minimally coupled Einstein–Hilbert action on the Einstein frame. The scalar potential is selected by the Noether symmetry approach in order to obtain conserved quantities for the FRW cosmological model. Exact solutions are obtained and analyzed in the context of the cosmological scenarios consistent with an expanding universe. A particular case is matched in each frame and the role of scalar field as a dark energy component is discussed.

Non-minimally coupled nonlinear spinor field in FRW cosmology

Within the scope of a FRW cosmological model we have studied the role of spinor field in the evolution of the Universe when it is non-minimally coupled to the gravitational one. We have considered a few types of nonlinearity. It was found that if the spinor field nonlinearity describes an ordinary matter such as radiation, the presence of non-minimality becomes essential and leads to the rapid expansion of the Universe, whereas if the spinor field nonlinearity describes a dark energy, the evolution of the Universe is dominated by it and the difference between the minimal and non-minimally coupled cases become almost indistinguishable.

A stable flat entropy-corrected FRW universe

In this paper, a general entropy-corrected FRW cosmological model has been presented in which a deceleration-to-acceleration transition occurs according to recent observations. We found that the case for the flat universe ([Formula: see text]), supported by observations, is the most stable one where it successfully passes all stability tests. The stability of the model has been studied through testing the sound speed, the classical and the new nonlinear energy conditions. The model predicts a positive pressure during the early-time decelerating epoch, and a negative pressure during the late-time accelerating epoch in a good agreement with cosmic history and dark energy assumption. We have investigated all possible values of the prefactors [Formula: see text] and [Formula: see text] in the corrected entropy-area relation to find the best values required for a stable flat universe. We have also made use of the evolution of the equation of state parameters [Formula: see text] in predicting the correct values of [Formula: see text] and [Formula: see text]. The jerk and density parameters have been calculated where a good agreement with observations and [Formula: see text]CDM model has been obtained. Two dark energy proposals have been investigated in this model, the entropy-corrected holographic dark energy and the modified holographic Ricci dark energy.

The effective dark energy in brane universe

We study the dynamical system of braneworld cosmology with the effective cosmological constant as the effective dark energy on brane universe. Firstly we introduce several scenarios of braneworld model then derive the effective EFE on the brane which reduced at low energy limit. Next, we discuss the FRW cosmological model in braneworld scenario considered in static and non-closed system. In the dynamical study of cosmology, we assume the equation of state of dark energy varies with time and can be parameterized as a function of scale factor of the universe. Using the dynamical system approach, we describe the evolution of brane universe with non-vanishing NCC/BCC term. In this study, we investigate the effects of the presence of NCC/BCC perturbations in brane universe. Finally, we discuss the NCC/BCC perturbations in the late-time cosmic acceleration when the dark energy contribution is ΩΛ ≃ 0.72.

Kaluza Klein Type FRW Cosmological Model With Extended Chaplygin Gas

In this paper we consider the extended Chaplygin gas equation of state as a model of dark energy for which it recovers barotropic fluids with quadratic equation of state. We obtain scale factor dependence energy density and Hubble expansion parameter for particular values of n, m and α. Similarly for arbitrary values of n, m and α we have discuss nature of cosmological parameters such as scale factor, Hubble expansion parameter, time dependent dark energy density and deceleration parameter in the framework of Kaluza Klein type FRW cosmological model. Further, we study stability of the model by using speed of sound and observe that the model is stable at late time.

A stable flat universe with variable cosmological constant in f(R, T) gravity

In this paper, a general FRW cosmological model has been constructed in f(R,T) gravity reconstruction with variable cosmological constant. A number of solutions to the field equations has been generated by utilizing a form for the Hubble parameter that leads to Berman’s law of constant deceleration parameter q = m − 1. The possible decelerating and accelerating solutions have been investigated. For (q > 0) we get a stable flat decelerating radiation-dominated universe at q = 1. For (q < 0) we get a stable accelerating solution describing a flat universe with positive energy density and negative cosmological constant. Nonconventional mechanisms that are expected to address the late-time acceleration with negative cosmological constant have been discussed.

Singularities in particle-like description of FRW cosmology

In this paper, we apply the method of reducing the dynamics of FRW cosmological models with a barotropic form of the equation of state to the dynamical system of the Newtonian type to detect the finite scale factor singularities and the finite-time singularities. In this approach all information concerning the dynamics of the system is contained in a diagram of the potential function V(a) of the scale factor. Singularities of the finite scale factor make themselves manifest by poles of the potential function. In our approach the different types of singularities are represented by critical exponents in the power-law approximation of the potential. The classification can be given in terms of these exponents. We have found that the pole singularity can mimic an inflation epoch. We demonstrate that the cosmological singularities can be investigated in terms of the critical exponents of the potential function of the cosmological dynamical systems. We assume that the general form of the model contains matter and some kind of dark energy which is parameterised by the potential. We distinguish singularities (by an ansatz involving the Lagrangian) of the pole type with the inflation and demonstrate that such a singularity can appear in the past.