In this article, we investigate the modified symmetric teleparallel gravity or $f(Q)$ gravity, where $Q$ is the non-metricity, to study the evolutionary history of the universe by considering the functional form of $f(Q)=αQ^n$, where $α$ and $n$ are constants. Here, we consider the parametrization form of the deceleration parameter as $q=q_0+\frac{q_1\,z}{(1+z)^2}$ which provides the desired property for sign flip from a decelerating to an accelerating phase. We get the solution of the Hubble parameter by examining the mentioned parametric form of $q$, and then we impose the solution in Friedmann equations. Employing the Bayesian analysis for the Observational Hubble data (OHD), we estimated the constraints on the associated free parameters $(H_0,q_0,q_1)$ to determine if this model may challenge the $Λ$CDM limitations. Furthermore, the constrained current value of the deceleration parameter $q_0=-0.832^{+0.091}_{-0.091}$ shows that the present universe is accelerating. We also investigate the evolutionary trajectory of energy density, pressure, and EoS parameters to conclude the accelerating behavior of the universe. Finally, we try to demonstrate that the considered parametric form of the deceleration parameter is compatible with $f(Q)$ gravity.
A spatially homogeneous anisotropic LRS Bianchi type-I cosmological model is studied in $f(R,T)$ gravity with a special form of Hubble's parameter, which leads to constant deceleration parameter. The parameters involved in the considered form of Hubble parameter can be tuned to match, our models with the $Λ$CDM model. With the present observed value of the deceleration parameter, we have discussed physical and kinematical properties of a specific model. Moreover, we have discussed the cosmological distances for our model.
The phenomenon of accelerated expansion of the present universe and a cosmic transit aspect is explored in the framework of a modified gravity theory known as $f(R,T)$ gravity (where $R$ is the Ricci scalar and $T$ is the trace of the energy momentum tensor of the matter content). The cosmic transit phenomenon signifies a signature flipping behaviour of the deceleration parameter. We employ a periodic varying deceleration parameter and obtained the exact solution of field equations. The dynamical features of the model including the oscillatory behaviour of the EOS parameter are studied. We hav…
We present a theory of weak gravity parameterized by a fundamental frequency $ω_0 = \sqrt{1-q}H$ of the cosmoloogical horizon, where $H$ and $q$ denote the Hubble and, respectively, deceleration parameter. It predicts (i) a $C^0$ onset to weak gravity across accelerations $α= a_{dS}$ in galaxy rotation curves, where $a_{dS}=cH$ denotes the de Sitter acceleration with velocity of light $c$, and (ii) fast evolution $Q(z)=dq(z)/dz$ of the deceleration parameter by $Λ=ω_0^2$ satisfying $Q_0>2.5$, $Q_0=Q(0)$, distinct from $Q_0\lesssim1$ in $Λ$CDM. The first is identified in high resolution data of…
The objective of this work enclosed with the study of spatially homogeneous anisotropic Bianchi type-I universe in $f(R,T)$ gravity (where $R$ is the Ricci scalar and $T$ is the trace of stress energy momentum tensor) in two different cases viz. $f(R,T)=R+2f(T)$ and $f(R,T)=f_1(R)+f_2(T)$ with bulk viscosity matter content. In this study, we consider a time varying deceleration parameter, which generates an accelerating universe to obtain the exact solution of the field equations. The physical and kinematical properties of both the models are discussed in detail for the future evolution of the…
We study an extension of symmetric teleparallel gravity i.e. Weyl-type $f(Q,T)$ gravity and the divergence-free parametrization of the deceleration parameter $q(z) = q_{0}+q_{1}\frac{z(1+z)}{1+z^2}$ ($q_{0}$ and $q_{1}$ are free constants) to explore the evolution of the universe. By considering the above parametric form of $q$, we derive the Hubble solution and further impose it in the Friedmann equations of Weyl-type $f(Q, T)$ gravity. To see whether this model can challenge the $Λ$CDM limits, we computed the constraints on the model parameters using the Bayesian analysis for the Observation…
We discuss the cosmological reconstruction in modified Gauss-Bonnet and F(R) gravities. Two alternative representations of the action (with and without auxiliary scalar) are considered. The approximate description of deceleration-acceleration transition cosmologies is reconstructed. It is shown that cosmological solution containing Big Bang and Big Rip singularities may be reconstructed only using the representation with the auxiliary field. The analytical description of the deceleration-acceleration transition cosmology in modified Gauss-Bonnet gravity is demonstrated to be impossible at suff…
In this paper, we have studied homogeneous and anisotropic, locally rotationally symmetric (LRS) Bianchi type-I universe model with magnetized strange quark matter (MSQM) distribution and cosmological constant $Λ$ in $f(R,T)$ gravity. The exact solutions of the field equations are obtained under bilinear and special form of time varying deceleration parameter (DP). Firstly we have considered two specific form of bilinear DP with a single parameter of the form: $q=\frac{α(1-t)}{1+t}$ and $q=-\frac{αt}{1+t}$, which leads to a function with constant or linear nature with respect to the choice of …
In this paper, we study the dynamical behaviour of the Universe in the $F(R,G)$ theory of gravity, where $R$ and $G$ respectively denote the Ricci scalar and Gauss-Bonnet invariant. Our wide analysis encompasses the energy conditions, cosmographic parameters, $Om(z)$ diagnostic, stability and the viability of reconstructing the referred model through a scalar field formalism. The model obtained here shows the quintessence like behaviour at late times.
In this letter, we have considered generalized Ricci dark energy in the Horava-Lifshitz gravity. We have reconstructed the Hubble's parameter in terms of fractional densities. We have viewed the equation of state parameter in this situation. Also, we have examined the behavior of deceleration parameter and investigated the nature of the statefinder diagnostics. The equation of state parameter has exhibited quintessence-like behavior and from the plot of the deceleration parameter we have observed an ever accelerating universe.
The present paper reports a study on the cosmological consequences arising from reconstructing $f(T)$ gravity through new holographic-polytropic dark energy. We assume two approaches, namely a particular form of Hubble parameter $H$ and a solution for $f(T)$. We obtain the deceleration parameter, effective equation of state as well as torsion equation of state parameters from total density and pressure in both cases. It is interesting to mention here that the deceleration and torsion equation of state represent transition from deceleration to acceleration phase. We study the statefinder parame…
A detailed study of the various cosmological aspects in massive gravity theory has been presented in the present work. For the homogeneous and isotropic FLRW model, the deceleration parameter has been evaluated, and, it has been examined whether there is any transition from deceleration to acceleration in recent past, or not. With the proper choice of the free parameters, it has been shown that the massive gravity theory is equivalent to Einstein gravity with a modified Newtonian gravitational constant together with a negative cosmological constant. Also, in this context, it has been examined …
In this work, we study a cosmological model of Bianchi type-I Universe in teleparallel gravity for a perfect fluid. To obtain the cosmological solution of the model, we assume that the deceleration parameter is a linear function of the Hubble parameter $H$ i.e. $q=-1+βH$ (where $β$ as a positive constant). Consequently, we get a model of our Universe, where it goes from the initial phase of deceleration to the current phase of acceleration. We have discussed some physical and geometric properties such as Hubble parameter, deceleration parameter, energy density, pressure, and equation of state …
We obtain the analogues of the Friedman equations in an emergent gravity scenario in the presence of dark energy. The background metric is taken to be Friedman-Lemaitre-Robertson-Walker (FLRW). We show that if $\dotϕ^{2}$ is the dark energy density (in units of the critical density) then (a) for total energy density greater than the pressure (non-relativistic scenario, matter domination) the deceleration parameter $q(t)\approx\frac {1}{2} [1 + 27 \dotϕ^{2}+...] > \frac{1}{2}$ (b) for total energy density equal to 3 times the pressure (relativistic case, radiation domination), the deceleration …
We study the periodic cosmic transit behavior of accelerated universe in the framework of symmetric teleparallelism. The exact solution of field equations is obtained by employing a well known deceleration parameter (DP) called periodic varying deceleration parameter (PVDP), $q = m cos kt-1$. The viability and physical reliability of the DP are studied by using the observational constraint. The dynamics of periodicity and singularity are addressed in details with respect to time and redshift parameter. Several ECs are discussed in this setting.
We studied plane symmetric cosmological model in the presence of quark and strange quark matter with the help of f(R,T) theory. To decipher solutions of Plane symmetric space-time, we used power law relation between scale factor and deceleration parameter. We considered the special law of variation of Hubble's parameter proposed by Berman (Nuovo Cimento B 74, 182, 1983) which yields constant deceleration parameter. We also discussed the physical behavior of the solutions by using some physical parameters.
In this paper we study the occurrence of accelerating universe versus decelerating universe between the F(R) gravity frame (Jordan frame) and non-minimally coupled scalar field theory frame, and the minimally coupled scalar field theory frame (Einstein frame) for various models. As we show, if acceleration is imposed in one frame, it will not necessarily correspond to an accelerating metric when transformed in another frame. As we will demonstrate, this issue is model and frame-dependent but it seems there is no general scheme which permits to classify such cases.
We study an special law for the deceleration parameter, recently proposed by Akarsu and Dereli, in the context of $f(R)$, $f(T)$ and $f(\mathcal{G})$ theories of modified gravity. This law covers the law of Berman for obtaining exact cosmological models to account for the current acceleration of the universe, and also gives the opportunity to generalize many of the dark energy models having better consistency with the cosmological observations. Our aim is to reconstruct the $f(R)$, $f(T)$ and $f(\mathcal{G})$ models inspired by this law of variable deceleration parameter. Such models may then …
This paper is devoted to investigate the anisotropic locally rotationally symmetric (LRS) Bianchi type-I space-time in the context of the recently proposed $f(Q)$ gravity in which $Q$ is the non-metricity scalar. For this purpose, we consider a linear form of $f\left( Q\right) $ gravity model, specifically, $f\left( Q\right) =αQ+β$, where $α$ and $% β$ are free parameters and we analyzed the exact solutions of LRS Bianchi type-I space-time. The modified Friedmann equations are solved by presuming an expansion scalar $θ\left( t\right) $ is proportional to the shear scalar $σ\left( t\right) $ wh…
Comparative Analysis of Perturbed $f(R)$ Gravity and Perturbed Rastall Gravity Models in Describing Cosmic Evolution from Early to Late Universe Relative to the $Λ$CDM Model
We examine the observational viability of a class of $f(\mathcal{R})$ gravity cosmological models. Particular attention is devoted to constraints from the recent observational determination of the redshift of the cosmological deceleration-acceleration transition. Making use of the fact that the Ricci scalar is a function of redshift $z$ in these models, $\mathcal {R=R}(z)$, and so is $f(z)$, we use cosmography to relate a $f(z)$ test function evaluated at higher $z$ to late-time cosmographic bounds. First, we consider a model independent procedure to build up a numerical $f(z)$ by requiring th…
This paper deals with a spatially homogeneous and totally anisotropic Bianchi type-V cosmological model within the framework of self interacting Brans Dicke theory of gravity in the background of anisotropic dark energy (DE) with variable equation of state (EoS) parameter and constant deceleration parameter. Constant deceleration parameter leads to two models of universe, i.e. power law model and exponential model. EoS parameter ω and its existing range for the models is in good agreement with the most recent observational data. We notice that ω given by (37) i.e ω(t) = log(k1t) is more suitab…
We present the coupling of the torsion scalar $T$ and the trace of energy-momentum tensor $\mathcal{T}$, which produces new modified $f(T,\mathcal{T})$ gravity. Moreover, we consider the functional form $f(T,\mathcal{T}) =α\mathcal{T}+βT^2$ where $α$ and $β$ are free parameters. As an alternative to a cosmological constant, the $f(T,\mathcal{T})$ theory may offer a theoretical explanation of the late-time acceleration. The recent observational data to the considered model especially the bounds on model parameters is applied in detail. Furthermore, we analyze the cosmological behavior of the de…
We study non-viscous and viscous holographic dark energy models for a homogeneous and isotropic flat Friedmann-Robertson-Walker Universe in $f(R,T)$ gravity. We find that the Hubble horizon as an IR cut-off is suitable for both the models to explain the recent accelerated expansion of the Universe. The cosmological parameters like deceleration parameter and statefinder parameters are discussed in each model. In non-viscous model a constant deceleration parameter is found which shows that there is no phase transition. The constraints on the parameters are obtained to analyse the fixed point val…
Recently, the cosmological deceleration-acceleration transition redshift in $f(R)$ gravity has been considered in order to address consistently the problem of cosmic evolution. It is possible to show that the deceleration parameter changes sign at a given redshift according to observational data. Furthermore, a $f(R)$ gravity cosmological model can be constructed in brane-antibrane system starting from the very early universe and accounting for the cosmological redshift at all phases of cosmic history, from inflation to late time acceleration. Here we propose a $f(R)$ model where transition re…
We study the present, flat isotropic universe in 1/R-modified gravity. We use the Palatini (metric-affine) variational principle and the Einstein (metric-compatible connected) conformal frame. We show that the energy density scaling deviates from the usual scaling for nonrelativistic matter, and the largest deviation occurs in the present epoch. We find that the current deceleration parameter derived from the apparent matter density parameter is consistent with observations. There is also a small overlap between the predicted and observed values for the redshift derivative of the deceleration …
Here, RS-II model of brane-gravity is considerd for phantom universe using non-linear equation of stste. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension $λ$ of the RS-II model. It is interesting to see that upto a certain value of energy density $ρ$ satisfying $ρ/λ< 1$, weak energy condition is violated and universe super-accelerates. But as $ρ$ increases more, only strong energy condition is violated and universe accelerates. When $1 < ρ/λ<2$, even strong en…
We study the energy conditions in the framework of the modi- fied gravity with higher-derivative torsional terms in the action. We discuss the viability of the model by studying the energy conditions in terms of the cosmographical parameters like Hubble, deceleration, jerk, snap and lerk parameters. In particular, We consider two spe- cific models that are proposed in literature and examine the viability bounds imposed by the weak energy condition.
In this paper we obtain some cosmological solutions that describe the present period of accelerating expansion of the universe in the framework of a geometrical gauge scalar-tensor theory of gravity. The background geometry in the model is the Weyl integrable and we found a class of power law solutions for the Weyl scalar field when an invariant metric is employed in a power law expanding universe. We obtain a deceleration and an equation of state parameters in agreement with PLANCK 2018 observational data for some specific parameters of the model. The deceleration parameter tends asymptotical…
The equation of state parameter is a significant method for characterizing dark energy models. We investigate the evolution of the equation of state parameter with redshift using a Bayesian analysis of recent observational datasets (the Cosmic Chronometer data (CC) and Pantheon samples). The Chevallier-Polarski-Linder parametrization of the effective equation of state parameter, $ω_{eff}=ω_0+ω_a \left( \frac{z}{1+z}\right) $, where $ω_0$ and $ω_a$ are free constants, is confined to the Weyl type $f(Q,T)$ gravity, where $Q$ represents the non-metricity and $T$ is the trace of the energy-momentu…
This paper is devoted to investigate the exact solutions of Bianchi types I and V spacetimes in the context of f(R, T) gravity [1]. For this purpose, we found two exact solutions in each case by using assumption of constant deceleration parameter and the variation law of Hubble parameter. The obtained solutions correspond to two different models of this universe. The physical behavior of these models is also discussed.
We discuss the recently suggested Ricci-Gauss-Bonnet holographic dark energy in Chern-Simons modified gravity. We have tested some general forms of the scale factor $a(t)$, and used two physically reasonable forms which have been proved to be consistent with observations. Both solutions predict a sign flipping in the evolution of cosmic pressure which is positive during the early-time deceleration and negative during the late-time acceleration. This sign flipping in the evolution of cosmic pressure helps in explaining the cosmic deceleration-acceleration transition, and it has appeared in othe…
Here, cosmology of the late and future universe is obtained from $f(R)$-gravity with non-linear curvature terms $R^2$ and $R^3$ ($R$ being the Ricci scalar curvature). It is different from $f(R)$-dark enrgy models, where non-linear curvature terms are taken as gravitational alternative of dark energy. In the present model, neither linear nor no-linear curvature terms are taken as dark energy. Rather, dark energy terms are induced by curvature terms in the Friedmann equation derived from $f(R)$-gravitational equations. It has advantage over $f(R)$- dark energy models in the sense that the prese…
In this paper, we study three models of f(R) modified gravity including higher order terms based on different equation of state parameter. We also assume variable G and $Λ$. By using numerical analysis, we obtain the behavior of some important cosmological parameters, like the Hubble expansion H parameter and the deceleration parameter q. The statefinder diagnostics is also performed for all models.
In this work, we have studied the traversable wormholes geometry in $f(R)$ theory gravity, where $R$ be the Ricci scalar. The wormhole solution for some assumed $f(R)$ functions have been presented. The assumption of $f(R)$ is based on the fact that its behaviour changed with an assumed parameter $α$ rather than the deceleration parameter. Three models are presented based on the physically motivated shape function and their behaviours are studied.
In this paper, we have derived the field equations in an extended theory of gravity in an anisotropic space time background and in the presence of magnetic field. The physical and geometrical parameters of the models are determined with respect to the Hubble parameter using some algebraic approaches. A time varying scale factor has been introduced to analyze the behavior of the model. From some diagnostic approach, we found that the model behaves as $Λ_{CDM}$ model at late time of cosmic evolution.
In this work, we have developed an FLRW type model of a universe which displays transition from deceleration in the past to the acceleration at the present. For this, we have considered field equations of $f(R,T)$ gravity and have taken $f(R,T) = R + 2 λT$, $λ$ being an arbitrary constant. We have estimated the $λ$ parameter in such a way that the transition red shift is found similar in the deceleration parameter, pressure and the equation of state parameter $ω$. The present value of Hubble parameter is estimated on the basis of the three types of observational data set: latest compilation of…
In the current framework of Einstein's equations in general relativity (GR), gravity is described by the spacetime curvature. However, there are other descriptions where the origin of gravity can be understood through torsion and non-metricity $Q$. In this work, we discuss a modified theory of gravity namely $f(Q)$ gravity, which considers a non-linear extension of $Q$. In particular, we study the case where it is non-minimally coupled to matter. Motivated by the recent success of Chaplygin gas models in the explanation of dark energy, we assume a pressureless baryonic matter and a generalized…
We use the hybrid model of bulk viscosity and generalized chaplygin gas (GCG), named the viscous generalized chaplygin gas (VGCG) model, which is thought to be an alternate dark fluid of the universe. We explore the dynamics of the VGCG model in the framework of the non-metricity $f(Q)$ gravity using the functional form $f(Q)=βQ^n$, where $β$ and $n$ are arbitrary constants. For the purpose of constraining model parameters, we use recent observational datasets such as Observational Hubble data, Baryon Acoustic Oscillations, and Type $Ia$ supernovae data. According to our study, the evolution o…
In this paper we have studied Kaluza-Klein string cosmological model within the framework of f(R; T) theory of gravity, where R is the Ricci scalar and T is the trace of the stress energy momentum tensor. We have obtained the solution of the corresponding field equations by using a time varying deceleration parameter. We also discussed various physical and dynamical properties of the model. The variation of different cosmological parameters are shown graphically for specific values of the parameters of the model.
This paper is devoted to investigate the exact solutions of Bianchi type $I$ spacetime in the context of $f(R,T)$ gravity [1], where $f(R,T)$ is an arbitrary function of Ricci scalar $R$ and trace of the energy momentum tensor $T$. For this purpose, we find two exact solutions using the assumption of constant deceleration parameter and variation law of Hubble parameter. The obtained solutions correspond to two different models of the universe. The physical behaviour of these models is also discussed.
The metric $f(R)$ theories of gravity are generalized to five-dimensional spacetimes. By assuming a hypersurface-orthogonal Killing vector field representing the compact fifth dimension, the five-dimensional theories are reduced to their four-dimensional formalism. Then we study the cosmology of a special class of $f(R)=αR^m$ models in a spatially flat FRW spacetime. It is shown that the parameter $m$ can be constrained to a certain range by the current observed deceleration parameter, and its lower bound corresponds to the Kaluza-Klein theory. It turns out that both expansion and contraction …
In this paper we use the conformal teleparallel gravity to study an isotropic and homogeneous Universe which is settled by the FRW metric. We solve the field equations and we obtain the behavior of some cosmological parameters such as scale factor, deceleration parameter and the energy density of the perfect fluid which is the matter field of our model. The field equations, that we called modified Friedmann equations, allow us to define a dark fluid, with dark energy density and dark pressure, responsible for the acceleration in the Universe.
On the basis of homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) geometry, solutions to the issues of cosmic acceleration and dark energy are being put forth within the context of $f\left( Q\right)$ gravity. We take into account a power law $f(Q)$ model using $f\left( Q\right) =αQ^{n}$, where $α$ and $n$ are free model parameters. In the current scenario, we may establish the energy density and pressure for our $f(Q)$ cosmic model by applying the constant sound speed parameterizations, i.e., $\vartheta_{s}^{2}=β$, where a barotropic cosmic fluid is described in terms of $β$…
Modified gravity and generalized second law (GSL) of thermodynamics are interesting topics in the modern cosmology. In this regard, we investigate the GSL of gravitational thermodynamics in the framework of modified Gauss-Bonnet gravity or f(G)-gravity. We consider a spatially FRW universe filled with the matter and radiation enclosed by the dynamical apparent horizon with the Hawking temperature. For two viable f(G) models, we first numerically solve the set of differential equations governing the dynamics of f(G)-gravity. Then, we obtain the evolutions of the Hubble parameter, the Gauss-Bonn…
Recently a $f(T)$ gravity based on the modification of the teleparallel gravity was proposed to explain the accelerated expansion of the universe without the need of dark energy. We use observational data from Type Ia Supernovae, Baryon Acoustic Oscillations, and Cosmic Microwave Background to constrain this $f(T)$ theory and reconstruct the effective equation of state and the deceleration parameter. We obtain the best-fit values of parameters and find an interesting result that the $f(T)$ theory considered here allows for the accelerated Hubble expansion to be a transient effect.
We present a novel reconstruction method of $f(T)$ teleparallel gravity from phenomenological parameterizations of the deceleration parameter or other alternatives. This can be used as a toolkit to produce viable modified gravity scenarios directly related to cosmological observations. We test two parameterizations of the deceleration parameter considered in recent literatures in addition to one parametrization of the effective (total) equation of state (EoS) of the universe. We use the asymptotic behaviour of the matter density parameter as an extra constraint to identify the viable range of …
The aim of this paper is to analyze the cosmological evolution of holographic dark energy in $f(\mathcal{G},T)$ gravity ($\mathcal{G}$ and $T$ represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, respectively). We reconstruct $f(\mathcal{G},T)$ model through correspondence scheme using power-law form of the scale factor. The qualitative analysis of the derived model is investigated with the help of evolutionary trajectories of equation of state, deceleration as well as state-finder diagnostic parameters and $ω_{_{\mathcal{G}T}}-ω'_{_{\mathcal{G}T}}$ cosmological phase …
Recently, a new strategy to the reconstruction of $f(R)$-gravity models based on the Raychaudhuri equation has been suggested by Choudhury et al. In this paper, utilizing this method, the reconstruction of anisotropic Einstein-Maxwell equation in the $1+3$ covariant formalism of $f(R)$-gravity is investigated in four modes: $i.$ Reconstruction from a negative constant deceleration parameter refereeing to an ever-accelerating universe; $ii.$ Reconstruction from a constant jerk parameter $j=1$ which recovers celebrated $Λ\text{CDM}$ mode of evolution; $iii.$ Reconstruction from a variable jerk p…
In this work, we have considered Cardassian Universe in Horava-Lifshitz gravity. Four types of Cardassian Universe models i.e., polytropic/power law, modified polytropic, exponential and modified exponential models have been considered for accelerating models. The natures of statefinder parameters, deceleration parameter, Om diagnostic and EoS parameters have been investigated for all types of Cardassian models in Horava-Lifshitz gravity.
