arXiv subjects

Shaily

Publications and source records attributed to Shaily.

17 recordsLinked to original sources

arXiv2025

The cosmic consequences and the constraints on HN-gravity

In this paper, we investigate the latetime cosmic acceleration of the Quintessence model within the framework of Hoyle Narlikar Gravity (HNG), which incorporates a creation field. Using the Hubble tension as a function of the density parameter for matter, the density parameter for radiation, and the density parameter for dark energy in the covariant formulation, we find the gravitational field equations in the spatially flat, homogeneous, and isotropic spacetime to examine the dynamical mechanism that leads to cosmic acceleration in the late-time universe. We analyze the observational constraints on the latetime density parameters using various recent observational datasets, including the Hubble datasets, Pantheon plus, and the joint compilation, Pantheon BAO. Consequently, it is explicitly demonstrated that latetime cosmic acceleration can be consistent with recent observational data in Hoyle Narlikar Gravity with nonminimal matter interaction. In contrast with other modified theories of gravity, it is observed that the creation field theory with non minimal matter interaction renders more compact constraints on the Hubble tension together with density parameters, and extensively explains the accelerating expansion of the universe, which makes it a more plausible option compared to the LCDM model. Furthermore, the ww1 phase analysis confirms alternating thawing and freezing behaviour of the model, with all trajectories ultimately converging toward the LCDM point, thereby confirming the model stability and the observational consistency.

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arXiv2024

Cosmic reverberations on a constrained $ f(Q,T) $-model of the Universe

In this paper, we construct an isotropic cosmological model in the $ f(Q, T) $ theory of gravity in the frame of a flat FLRW spacetime being $ Q $ the non-metricity tensor and $ T $ the trace of the energy-momentum tensor. The gravity function is taken to be a quadratic equation, $ f(Q, T)=\zeta Q^2 + \gamma T $, where $ \zeta<0 $ and $ \gamma $ are the arbitrary constants. We constrain the model parameters $ \alpha $ and $ H_0 $ using the recent observational datasets: the Hubble dataset (OHD), the $ Pantheon $ dataset of $ 1048 $ points, and the joint dataset (OHD + $ Pantheon $). The universe model transitions from an early deceleration state to an acceleration in late times. This model also provides the ekpyrotic phase of the universe on the redshift $ z>12.32 $. In this model, the Big Bang is described as a collision of branes, and thus, the Big Bang is not the beginning of time. Before the Big Bang, there is an ekpyrotic phase with the equation of state $ \omega >> 1 $. In late times, the undeviating Hubble measurements reduce the $ H_0 $ tension in the reconstructed $ f(Q, T) $ function. Additionally, we study various physical parameters of the model. Finally, our model describes a quintessence dark energy model at later times.

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arXiv2024

Cosmic observation of a model in the horizon of $ f(Q, C) $-gravity

In this work, we developed a cosmological model in $ f(Q, C) $ gravity within the framework of symmetric teleparallel geometry. In addition to the non-metricity scalar $Q $, our formulation includes the boundary term $ C $, which accounts for its deviation from the standard Levi-Civita Ricci scalar $ R^* $ in the Lagrangian. We derived the field equations for the metric and affine connection, employed them within a cosmological setting, and a vanishing affine connection to derive modified Friedmann equations. We used the latest observational dataset OHD in the redshift range $ z \in [0, 2.36]$, Pantheon + SH0ES in the redshift range $ z \in (0.01, 2.26)$, BAO, and the joint datasets OHD + Pantheon + SH0ES and OHD + Pantheon + SH0ES + BAO to constrain the parameters of our model by employing Markov Chain Monte Carlo (MCMC) method to minimize the $\chi^2$ term. Using the constrained free model parameters, we carefully analyzed the behavior of different physical parameters and verified that the model transits from deceleration to acceleration. Finally, we observed that the model demonstrates an expanding quintessence dark energy model and converges to the $ \Lambda $CDM in later times.

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arXiv2024

Evolution of the universe with quintessence model in Rastall gravity

We investigate the universe's evolution within the framework of Rastall gravity, which is an extension of the standard $\Lambda$CDM model. Utilizing a linear parametrization of the Equation of State (EoS) in a Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) background, we constrain the model parameters through analysis of cosmic chronometers (CC), Pantheon, Gold, Gamma Ray Burst (GRB), and Baryon Acoustic Oscillations (BAO) datasets, as well as their joint analysis, under $1\sigma$ and $2\sigma$ confidence levels, considering the Rastall parameter $\lambda$. The constrained parameters are then used to compare our model with the standard $\Lambda$CDM model. Our findings include a detailed examination of the model's physical interpretations and demonstrate the potential for an accelerating universe expansion in later times, aligning with the observed behavior of dark energy.

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arXiv2024

Power law cosmology in Gauss-Bonnet gravity with pragmatic analysis

In this study, we present an approach $ f(R, G) $ gravity incorporating power law in $ G $. To study the cosmic evolution of the universe given by the reconstruction of the Hubble parameter given by $ E(z) = \bigg( 1+\frac{z(\alpha+(1+z)^{\beta})}{2 \beta + 1} \bigg)^{\frac{3}{2 \beta}} $. Subsequently, we use various recent observational datasets of OHD, Pantheon, and BAO to estimate the model parameters $ H_0,~\alpha $, and $ \beta $ applying the Markov Chain Monte Carlo (MCMC) technique in the emcee package to establish the validity of the model. In our findings, we observe that our model shows consistency with standard $ \Lambda $CDM, transits from deceleration to acceleration, and enters the quintessence region in late times. The cosmological model satisfies necessary energy constraints, simultaneously violating the strong energy condition (SEC), indicating a repulsive nature and consistent with accelerated expansion. The cosmic evolution of the Hawking temperature and the total entropy for the various observational datasets also show the validity of the model. Thus, our established model demonstrates sufficient potential for explicitly describing cosmological models.

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arXiv2024

The consequence of higher-order curvature-based constraints on $ f(R, L_m) $ gravity

In this investigation, we perform an observational statistical analysis in the theory of $ f(R, L_m) $ gravity. The proposed theoretical model is based on the Ricci scalar's non-linear contribution. We use a distinct parameterization for the deceleration parameter and constrain the model parameters by using various observational data. To determine the best-fit model for the cosmological parameters, we use different observational datasets such as the Hubble Space Telescope, the Pantheon Supernova Survey, the Gold dataset, the Gamma-Ray Burst (GRB), and the Baryon Acoustic Oscillations (BAO). Furthermore, we study the late-time cosmic evolution of the Universe in detail and examine the implications of the constraint values on cosmological parameters. Additionally, we conduct a thorough comparison with the standard cosmological model $ \Lambda $CDM and other standard models obtained by Odintsov et al. \cite{Odintsov:2023cli, Odintsov:2024lid} to examine the validity of our proposed model in the low-redshift regimes. Finally, we find that the proposed model encapsulates an intriguing transition from early deceleration at high redshift to acceleration at low redshift, a quintessence dark energy scenario, and convergence towards the well-established $ \Lambda $CDM model in late-time Universe's evolution.

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arXiv2024

Stability analysis of a dark energy model in Rastall gravity

We study a cosmological model in Rastall's theory of gravity in the framework of the flat FLRW metric. We formulate the value of the Hubble parameter, which contains two model parameters, $ \alpha $ and $ j $. Employing the Markov Chain Monte Carlo (MCMC) sampling technique, we determine the values of these model parameters along with their uncertainties. Moreover, we derive the equation of state (EoS) parameter, which converges around the quintessence region. We perform a dynamical system analysis using the linearization technique to validate the results independently. Also, we discuss various physical attributes of the model, highlighting the transition to acceleration and the violation of the strong energy condition (SEC) in the late stages of evolution. In conclusion, our model mimics the behavior of a dark matter fluid during the past epoch and transitions into a quintessence dark energy model in the future epoch.

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arXiv2024

Late time phantom characteristic of the model in $f(R,T)$ gravity with quadratic curvature term

We propose a novel cosmological framework within the $f(R,T)$ type modified gravity theory, incorporating a non-minimally coupled with the higher order of the Ricci scalar ($R$) as well as the trace of the energy-momentum tensor ($T$). Therefore, our well-motivated chosen $f(R,T)$ expression is $ R + R^m + 2 \lambda T^n$, where $\lambda$, $m$, and $n$ are arbitrary constants. Taking a constant jerk parameter ($j$), we derive expressions for the deceleration parameter ($q$) and the Hubble parameter ($H$) as functions of the redshift $z$. We constrained our model with the recent Observational Hubble Dataset (OHD), $Pantheon$, and $ Pantheon $ + OHD datasets by using the analysis of Markov Chain Monte Carlo (MCMC). Our model shows early deceleration followed by late-time acceleration, with the transition occurring in the redshift range $1.10 \leq z_{tr} \leq 1.15$. Our findings suggest that this higher-order model of $f(R,T)$ gravity theory can efficiently provide a dark energy model for addressing the current scenario of cosmic acceleration.

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arXiv2023

Observational Constraints and Cosmographic Analysis of $f({T},{T}_{{G}})$ Gravity and Cosmology

We perform observational confrontation and cosmographic analysis of $f(T,T_G)$ gravity and cosmology. This higher-order torsional gravity is based on both the torsion scalar, as well as on the teleparallel equivalent of the Gauss--Bonnet combination, and gives rise to an effective dark-energy sector which depends on the extra torsion contributions. We employ observational data from the Hubble function and supernova Type Ia Pantheon datasets, applying a Markov chain Monte Carlo sampling technique, and we provide the iso-likelihood contours, as well as the best-fit values for the parameters of the power-law model, an ansatz which is expected to be a good approximation of most realistic deviations from general relativity. Additionally, we reconstruct the effective dark-energy equation-of-state parameter, which exhibits a quintessence-like behavior, while in the future the Universe enters into the phantom regime, before it tends asymptotically to the cosmological constant value. Furthermore, we perform a detailed cosmographic analysis, examining the deceleration, jerk, snap, and lerk parameters, showing that the transition to acceleration occurs in the redshift range $ 0.52 \leq z_{tr} \leq 0.89 $, as well as the preference of the scenario for quintessence-like behavior. Finally, we apply the Om

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arXiv2023

EDSFD parametrization in $ f(R,T) $ gravity with linear curvature terms

This paper investigates the flat Friedmann-Lema$\hat{\imath}$tre-Robertson-Walker (FLRW) cosmological model using a suitable parameterization represented as a differential equation concerning the energy density of the scalar field, $\rho_{\phi}$, in the context of $f(R,T)$ gravity theory. This parameterization is known as the Energy Density Scalar Field Differential Equation (EDSFD) parametrization. It results in a solution of the Hubble parameter containing four model parameters, namely, $\Omega_{m0},\Omega_{\phi 0}, H_0,$ and $\alpha$. To constrain the model parameters, $77$ data points from the Hubble dataset, $1048$ points from the Pantheon dataset, and $6$ data points from BAO are used. Using the constrained values, we analyze and compare our model with the standard $\Lambda$CDM model. The evolution of the physical parameters, which includes the deceleration parameter, density parameter, Equation of State (EoS) for Dark Energy, and $Om(z)$ diagnostic, are discussed.

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arXiv2023

A non-singular bouncing cosmology in $ f(R,T) $ gravity

We investigate a bounce realization in the framework of higher order curvature in $ f(R,T) $ modified theory of gravity. We perform a detailed analysis of the cosmological parameters to explain the contraction phase, the bounce phase, and the expansion phase. Furthermore, we observe a violation of the null energy condition, instability of the model, and a singularity upon deceleration at the bouncing point, which are the supporting results for a bouncing cosmology. The outcome of the slow roll parameters is satisfactory to understand the inflation era and the equation of state parameter exhibits a ghost condensate behavior of the model near the bounce. Additionally, we discuss the stability of the model using linear perturbations in the Hubble parameter as well as the energy density.

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arXiv2023

Power law cosmology in modified theory with thermodynamics analysis

In this paper, we consider a cosmological model in $ f(R, G) $ gravity in a flat space-time, where $ R $ is the Ricci scalar and $ G $ is the Gauss-Bonnet invariant. The function $ f(R, G) $ is taken as a linear combination of $ R $ and an exponential function of $ G $. We analyze the observational constraints under a power law cosmology which depends on two physical parameters: the Hubble constant $ H_0 $ and the deceleration parameter $ q $. We constrain these two dependent parameters using the latest 77 points of the OHD data, 1048 points of the Pantheon data, and the joint data OHD+Pantheon and compare the results with the $ \Lambda $CDM. Also, we speculate constraints using a simulated data set for the future JDEM (Joint Dark Energy Mission)/Omega, supernovae survey. We see that $ H_0 $ is in very close agreement with some of the latest results from the Planck Collaboration that assume the $ \Lambda $CDM model. Our work in power law cosmology better fits the Pantheon data than the earlier analysis \cite{Kumar:2011sw, Rani:2014sia}. However, the constraints obtained on $ H $ average, $ $ and $ q $ average, $ $ using the simulated data set for the future JDEM/Omega, supernovae survey are found to be inconsistent with the values obtained from the OHD and the Pantheon data. Additionally, we discuss statefinder diagnostics and see that the power law models approach the standard $\Lambda $CDM model ($ q\rightarrow -1 $). This model satisfies the Generalized Second Law of Thermodynamics. Finally, we conclude that the power law cosmology in $ f(R, G) $ gravity explains most of the distinguished attributes of evolution in cosmology.

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arXiv2022

The cosmological model in $ f(R,T^\phi) $ gravity with Scalar Field conformity

The homogeneous and isotropic cosmological model in generalized $ f(R,T^\phi) $ theories associated with scalar field is discussed, which is motivated by the $ f(R,T) $ theory of gravity studied by Harko et al. \cite{Harko:2011kv, Harko:2014pqa}. The $ f(R,T^\phi) $ gravity can be explained as $ f(R,T) $ gravity with a self-interacting scalar field $ \phi $, where $ T^\phi $ is the trace of the energy-momentum tensor. The parametrization of Hubble parameter $ H(t) $ is taken as $ \alpha-\beta e^{-\gamma t} $, where $ \alpha $, $\beta$ and $\gamma$ are arbitrary constants such that $ \alpha, \gamma>0 $ and $ \beta<0 $. The model shows no space-time singularity and the expansion of the universe will continue forever, i.e., the future scenario of the universe attains Big Freeze. The model predicts the moderate inflationary scenario at the time of the evolution of the universe and it is consistent with $ \Lambda $CDM in late times. The consistency of the model has also been examined using recent observational Hubble dataset and supernovae dataset. Finally, the physical features of the model have been discussed in some detail.

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arXiv2022

A constrained cosmological model in $f(R,L_m)$ gravity

In this article, we study the expanding nature of universe in the contest of $f(R,L_m)$ gravity theory, here $ R $ represents the Ricci scalar and $ L_m $ is the matter Lagrangian density. With a specific form of $ f(R,L_m) $, we obtain the field equations for flat FLRW metric. We parametrize the deceleration parameter in terms of the Hubble parameter and from here we find four free parameters, which are constraints and estimated by using $H(z)$, $Pantheon$, and their joint data sets. Further, we investigate the evolution of the deceleration parameter which depicts a transition from the deceleration to acceleration phases of the universe. The evolution behaviour of energy density, pressure, and EoS parameters shows that the present model is an accelerated quintessence dark energy model. To compare our model with the $ \Lambda $CDM model we use some of the diagnostic techniques. Thus, we find that our model in $ f(R,L_m) $ gravity supports the recent standard observational studies and delineates the late-time cosmic acceleration.

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arXiv2022

The constrained cosmological model in Lyra geometry

In this article, we study a flat homogeneous FLRW model in Lyra geometry which is described by a time-dependent displacement vector. We consider an appropriate parametrization of the energy density of scalar field $ \rho_\phi $ in terms of the cosmic scale factor. The result shows two transitions from deceleration to acceleration. Furthermore, we constrain the model parameter $ \alpha $ and the displacement field vector $ \beta $ using the recent supernovae data, Hubble data set of 77 points, and their joint data which predicts the accelerated expanding phase of the universe in late times. The effective equation of state parameter $ \omega_{eff} $ speculate $ \Lambda $CDM in late times. Finally, we use the statefinder diagnostic to differentiate our model from the various dark energy models.

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arXiv2022

Dynamical analysis of a hyperbolic solution in Scale-covariant theory

We study an isotropic flat FLRW-model in Scale-covariant theory of gravity $ f_{\gamma \delta}(\phi) $ \cite{Canuto:1977zz} which is explained in terms of ordinary and covariant differentiation of scalar field $ \phi $. As we know the deceleration parameter is time-dependent, so we consider the deceleration parameter $ q $ as the function of $ t $. Using this methodology, we find all the important cosmological factors in terms of a hyperbolic function of the cosmic time $ t $. In turn, we create the model having the behavior of the late-time universe, which is ever accelerated expanding and faces a Big Freeze at the end. The model shows the quintessence dark energy model from early to late times. We compute the constrained values of Hubble parameter $ H_0=70.979^{+0.021}_{-0.0043} $ and the model parameter $ n=1.24079^{+0.00015}_{-0.00079} $ using joint analysis of the $ OHD $ data of 77-points and Pantheon bin data. The model exhibits point-type singularity, beginning with a point of zero volume, infinite energy density, and temperature. Furthermore, we obtain the present deceleration parameter $ (q_0) \approx {-0.54} $. Also, we examine the ultimate behavior of our model by properly analyzing energy conditions, cosmographical parameters, and Statefinder diagnostic. Finally, the proposed model behaves like a quintessence dark energy model.

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arXiv2022

Bouncing universe in Gauss-Bonnet gravity

In this paper, a bouncing cosmological scenario is studied in the background of a flat FLRW model with a specific parametrized hyperbolic form of scale factor $ a $ in terms of $ t $, where $ \lambda $ is taken as the model parameter. This model is discussed in $ f(R,G) $ formalism having structured as $ f(R,G)=R+F(G) $, where $ R $ is Ricci scalar and $ G $ is the Gauss-Bonnet invariant. The proposed functional form of the Hubble parameter is considered in such a way that it satisfies the bouncing criteria of the model, which is free from the initial singularity. The physical consequences of the model are discussed. In this model, one can see that the EoS parameter crosses the quintom line $ \omega=-1 $ in the neighborhood of bouncing point $ t\approx0 $, which is a very strong criterion for a successful bouncing cosmological model. Finally, we find that all the essential features of the bouncing model are satisfied successfully.

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