arXiv subjects

Vinod Kumar Bhardwaj

Publications and source records attributed to Vinod Kumar Bhardwaj.

At least 19 recordsLinked to original sources

arXiv2026

Observationally Constrained Cosmological model in $f(Q,\mathcal{L}_{m})$ Gravity with $H(z)$ parameterization

In the present work, we explore an observationally constrained cosmological model in the framework of $f(Q,\mathcal{L}_{m})$ gravity, where $Q$ denotes the non-metricity scalar and $\mathcal{L}_{m}$ represents the matter Lagrangian density. To derive the modified Friedmann field equations, we consider a flat FLRW space-time. We have considered a specific parameterization of the Hubble parameter $H(z)$ to explore the cosmic evolution, which successfully describes the shift of the cosmos from its initial decelerated expansion period to the current accelerated scenario. The free model parameters are constrained using recent observational datasets including Cosmic Chronometers (CC), Pantheon+SH0ES, Union 3.0, DESI-BAO, and CMB distance priors using MCMC approach through the $χ^2$-minimization process. The derived results indicate that the present model remains consistent with recent cosmological observations. We note that the deceleration parameter exhibits a signature flipping behavior at transition redshift $z_t \approx 0.643$, confirming the transition from matter-dominated deceleration to dark-energy-driven acceleration. The equation of state (EOS) parameter remains in the quintessence region and exhibits an asymptotical approach to the $Λ$CDM limit at late times. Moreover, the estimated cosmic age can be found as $13.724^{+0.087}_{-0.048}$ Gyr, which agrees well with recent observational estimations. The statefinder and Om diagnostics support the quintessence nature of the model. At the same time, the examination of energy conditions reveals that two specific energy conditions, viz. Null Energy Condition (NEC) and Dominant Energy Condition (DEC) are fulfilled, while the Strong Energy Condition (SEC) is violated, validating the accelerated expansion of the universe.

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arXiv2026

Cosmological Implications of the Gong-Zhang Parameterization in Rastall Gravity: A Deep Learning and Observational Study

In this study, we have explored the cosmological dynamics of an isotropic, homogeneous universe in Rastall gravity. For this purpose, we use the parameterization of the EoS parameter in the form $ω(z) = \frac{ω_{0}}{(z+1)} $ to derive the explicit solution of the field equations in Rastall gravity. We constrained the cosmological parameters for the derived model by the Markov Chain Monte Carlo (MCMC) approach utilizing OHD, BAO, and Pantheon plus compilation of SN Ia datasets. We also constrained the model parameters using deep learning techniques and the CoLFI Python package. This paper introduces an innovative deep-learning approach for parameter inference. The deep learning method significantly surpasses the MCMC technique regarding optimal fit values, parameter uncertainties, and relationships among parameters. This conclusion is drawn from a comparative analysis of the two methodologies. Additionally, we determined the transition redshift $z_t = 0.941$, which signifies the shift in the Universe's model from an early deceleration phase to the present acceleration phase. The diagnosis of the model with diagnostic tools like statefinders, jerk parameter, and $O_m$ diagnostics are presented and analyzed. The validation of the model's energy conditions is also examined.

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arXiv2025

Transitioning late-time cosmology with the Hubble parameterization

We investigate a late-time cosmological model for a homogeneous and isotropic space-time in the Rastall theory. We explore the observational constraints on the Hubble parameter by using the latest cosmological datasets such as cosmic microwave background radiation (Planck), baryon acoustic oscillations (DESI) and Type Ia Supernovae (Union 3.0). As a result, we explicitly demonstrate that the specific redshift transition occurs, namely, there happens a phase shift in the evolution of the universe from the initial deceleration era to the current accelerating phase of the cosmological scenario. Furthermore, we show that with the latest dataset of DESI-BAO clubbed with CC, CMB, and Union 3.0, the current value of the Hubble parameter is estimated as $H_0 = 66.945 \pm 1.094$, which can be compatible with the available observations.

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arXiv2025

Anisotropic cosmology using observational datasets: exploring via machine learning approaches

In the current study, we present the observational data constraints on the parameters space for an anisotropic cosmological model of Bianchi I type spacetime in general relativity (GR). For the analysis, we consider observational datasets of Cosmic Chronometers (CC), Baryon Acoustic Oscillation (BAO), and Cosmic Microwave Background Radiation (CMBR) peak parameters. The Markov chain Monte Carlo (MCMC) technique is utilized to constrain the best-fit values of the model parameters. For this purpose, we use the publicly available Python code from CosmoMC and have developed the contour plots with different constraint limits. For the joint dataset of CC, BAO, and CMBR, the parameter's best-fit values for the derived model are estimated as $ H_0 = 69.9\pm 1.4$ km/s/Mpc, $ Ω_{m0}=0.277^{+0.017}_{-0.015}$, $ Ω_{Λ0} = 0.722^{+0.015}_{-0.017}$, and $Ω_{σ0} = 0.0009\pm0.0001$. To estimate $H(z)$, we explore machine learning (ML) techniques like linear regression, Artificial Neural Network (ANN), and polynomial regression and thereafter analyze the results with the theoretically developed $H(z)$ for the proposed model. Among these ML techniques, the polynomial regression exceeds the performance compared to other techniques. Further, we also note that larger dataset provides a better understanding of the cosmological scenario in terms of ML view point.

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arXiv2025

Cosmological model in the framework of $f(R,\mathcal{L}_{m})$ gravity with quadratic equation of state parameter

In this study, we have explored a transitioning cosmological model of universe's expansion in $f(R,\mathcal{L}_{m})$ gravity. The quadratic type of equation of state parameter in the form $ω=-1 + α(1 + z) + β(1 + z)^2$, where $α$ and $β$ are constants, is considered to determine the explicit solution of field equations and derive Hubble parameter in term of redshift $z$. The model parameters are estimated taking observational datasets of BAO, Pantheon, and CC using MCMC analysis. Some dynamical properties like EOS parameter, energy density, pressure, and deceleration parameter are described. The cosmographic parameter like statefinders ($r,s$), jerk parameter ($j$) etc are also thoroughly explained. The energy conditions are also examined to validate the viability of the proposed model. We observe a transition redshift at $z_{t} = 0.942^{+0.112}_{-0.164}$ with the present value of deceleration parameter $q_0 = -0.4815^{+0.0362}_{-0.0096}$.

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arXiv2024

Constraining hybrid potential scalar field cosmological model in Lyra's geometry with recent observational data

In the current study, we investigate a scalar field cosmological model with Lyra's geometry to explain the present cosmic expansion in a homogeneous and isotropic flat FRW universe. In Einstein's field equations, we presupposed a variable displacement vector as an element of Lyra's geometry. In the context of the conventional theory of gravity, we suggest a suitable parameterization of the scalar field's dark energy density in the hybrid function of redshift $z$, confirming the essential transition behavior of the universe from a decelerating era to the present accelerated scenario. We present constraints on model parameters using the most recent observational data sets from OHD, BAO/CMB, and Pantheon, taking Markov Chain Monte Carlo (MCMC) analysis into account. For the proposed model, the best estimated values of parameters for the combined dataset (OHD, BAO/CMB, and Pantheon) are $ H_0 = 71.15\pm 0.26$ km/s/Mpc, $ Ω_{m0}=0.2625\pm 0.0024$, $ Ω_{\phi0} = 0.676\pm0.038$, $ α=-0.22\pm0.13$, $n = 0.096\pm0.079$, and $k = 0.38\pm0.32$. The model exhibits a flipping nature, and the redshift transition occurs at $z_t = 0.756^{+0.005}_{-0.015}$. The current value of the decelerated parameter for the proposed model is calculated as $q_0 = -0.625^{+0.067}_{-0.085}$ for the combined dataset. Some dynamical properties of the model like energy density ($ρ_ϕ$), scalar field pressure ($p_ϕ$), EoS parameter of scalar field ($ω_ϕ$), and effective EoS parameter ($ω_{eff}$) are analyzed and presented. Further, we have also examined the statefinder diagnosis and jerk parameters of the derived model. The total density parameter for the derived model is found to be unity which is in nice agreement with recent standard findings.

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arXiv2024

Observation constraints on scalar field cosmological model in Anisotropic universe

In this study, we have explored a scalar field cosmological model in the axially symmetric Bianchi type-I universe. In this study, our aim is to constrain the scalar field dark energy model in an anisotropic background. For this purpose, the explicit solution of the developed field equations for the model is determined and analysed. Constraints on the cosmological model parameters are established utilizing Markov Chain Monte Carlo (MCMC) analysis and using the latest observational data sets of OHD, BAO, and Pantheon. For the combined dataset (OHD, BAO, and Pantheon), the best-fit values of Hubble and density parameters are estimated as $ H_{0} = 71.54\pm 0.28$, $Ω_{m0}=0.2622\pm0.0021$ $Ω_{\phi0} = 0.7331\pm0.0046$, and $Ω_{σ0} = 0.000162\pm0.000063$. The model shows a flipping nature and redshift transition occurs at $z_{t} = 0.6964^{+0.0136}_{-0.0006}$, and the present value of decelerated parameter is computed to be $q_{0} = -0.6964\pm0.028$ for the combined dataset. We have explored characteristics like the universe's age, particle horizon, deceleration parameter, and jerk parameter. The dynamical properties such as energy density $ρ_ϕ$, scalar field pressure $p_ϕ$, and equation of state parameter $ω_ϕ$ are analyzed and presented. We have also described the behavior of the scalar potential $V(ϕ)$ and scalar fields. Furthermore, the authors also described the behavior of energy conditions in scalar-tensor cosmology. The scenario of the present accelerated expansion of the universe is described by the contribution of the scalar field.

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arXiv2024

Evaluation of Transit cosmological model in $f(R,T^ϕ)$ theory of gravity

We have explored a transitioning cosmic model, depicting late-time accelerated expansion in $f(R,T^ϕ)$ theory of gravity for an isotropic and homogeneous universe, where the trace of energy-momentum tensor $T^ϕ$ is the function of the self-interacting scalar field $ϕ$. We have proposed an explicit solution to the derived model by utilizing a scale factor of the hybrid form $a(t) = t^α e^{βt}$, where $α$ and $β$ are constants. To evaluate the best-fit values of free parameters of the suggested model, the statistical analysis based on the Markov Chain Monte Carlo (MCMC) method has been employed on 57 OHD points. We have described the dynamical features of the model like energy density, cosmic pressure, and equation of state parameter in the context of scalar field $ϕ$. We have also described the potential and behavior of the scalar field for quintessence and phantom scenarios. The deceleration parameter depicts a transitioning universe with signature flipping at $z_t = 0.82$ with the present value of deceleration parameter $q_0=-0.41$. The violation of SEC for the derived model indicates the cosmic expansion at a faster rate. We have used statefinders to diagnose the model. The findings for our theoretical model indicate that the derived model agrees with observed findings within a particular range of limitations.

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arXiv2023

Quintessence scalar field model in Weyl-type $f(Q,T)$ Gravity with $w_D-w'_D$ analysis

In the present study, we explore the dynamical characteristics of the quintessence cosmological model in Weyl-type $f(Q,T)$ gravity. Here, $T$ represents the trace of the matter energy-momentum tensor, and $Q$ symbolizes the nonmetricity tensor. We propose a solution to the field equation using the specific parametrization in the form$H(z) = H_{0} (1+z)^{1+α+β} e^{\left(\frac{- βz}{1+z}\right)}$, which depicts the necessary transition of cosmos from decelerating era to the current accelerating scenario. The values of model parameters are estimated as $H_0 = 71.17\pm 0.25 $, $α= -0.663\pm0.030$, and $β= 1.488\pm0.087$ using the MCMC analysis and limiting the model with a joint dataset of Pantheon, BAO, and OHD. We discuss the cosmic behavior of many features of the derived model like EoS parameters, energy density, and cosmic pressure. Further, we have also explored the cosmological behavior of the quintessence model in Weyl $f(Q,T)$gravity. We have described the cosmic behavior of the model by $ω_D-ω_D'$ analysis. The diagnosis of the model is also performed using state finders and jerk parameters. In the end, we have discussed the energy conditions for the proposed model. Our analysis shows that the suggested model is well consistent with the recent findings.

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arXiv2023

Exploring the Cosmological Model in $f(R,T^ϕ)$ Gravity with Observational Constraints

We have investigated an isotropic and homogeneous cosmological model of the universe in $f(R, T^ϕ)$ gravity, where $T^ϕ$ is the trace of the energy-momentum tensor and $R$ is the Ricci scalar. We developed and presented exact solutions of field equations of the proposed model by taking the parametrization $q(z) =α+ \frac{βz}{1+z}$, where $α$ and $β$ are arbitrary constants. The best possible values of the model's free parameters are estimated using the latest observational data sets of OHD, BAO, and Pantheon by applying the MCMC statistical technique. Some kinematic properties like density parameter $ρ_ϕ$, pressure $p_ϕ$, and equation of state parameter $ω_ϕ$ are derived. We have also discussed the behavior of the scalar potential $V(ϕ)$ in the $f(R, T^ϕ)$ gravity theory. The behaviors of scalar fields for quintessence and phantom models are explored. Furthermore, we have discussed the behavior of energy conditions and sound speed in $f(R, T^ϕ)$ cosmology.

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arXiv2023

Barrow entropic Quintessence and Dilation dark energy Models with Generalized HDE cut-off

In the present work, we have analyzed the behaviors of extension of generalized Barrow holographic dark energy(`BHDE'). A ``generalized BHDE model based on the particle and the future horizon using infrared cut-off" was proposed by Nojiri et al. (2022). In this work, we have reviewed the generalized BHDE extension under the assumption of a generalized HDE cut-off. Using a scale factor of the form $a = k t^m$, the dynamics of the cosmos have been discussed through graphic demonstration. By applying the ``open-source emcee Python package", the values of the free parameters $k$ and $m$ are estimated on 57 OHD points by the Markov Chain Monte Carlo (MCMC) technique. We have examined the behavior of the equation of state (EoS) parameter, $( p_{de})$, and dark energy density $(ρ_{de})$. We have also discussed the equivalence of holographic dark energy (DE) with the Barrow entropic DE and its extension. Also, we have explained quintessence and dilation dark energy models in the context of Barrow entropic DE.

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arXiv2022

Observational constraints for an axially symmetric transitioning model with bulk viscosity parameterization

In this paper, we have analyzed the significance of bulk viscosity in an axially symmetric Bianchi type-I model to study the accelerated expansion of the universe. We have considered four bulk viscosity parameterizations for the matter-dominated cosmological model. The function of the two significant Hubble $H(z)$ and deceleration parameters are discussed in detail. The energy parameters of the universe are computed using the most recent observational Hubble data (57 data points) in the redshift range $0.07 \leq z \leq 2.36)$. In this model, we obtained all feasible solutions with the viscous component and analyzed the universe's expansion history. Finally, we analyzed the statefinder diagnostic and found some interesting results. The outcomes of our developed model now properly align with observational results.

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arXiv2022

Thermodynamic properties, thermal image and phase transition of Einstein-Gauss-Bonnet black hole coupled with nonlinear electrodynamics

We obtain an exact solution of $AdS$ black hole solution in Einstein-Gauss-Bonnet (EGB) gravity coupled with nonlinear electrodynamics. It interpolates with the $AdS$ regular black hole and $AdS$ EGB black hole in the absence of the Gauss-Bonnet coupling constant and both magnetic monopole charge and deviation parameter, respectively. Based on horizon thermodynamics, we study the thermodynamic properties of the obtained solution (e.g. mass, temperature, entropy, heat capacity and free energy). The Hawking temperature of the nonsingular black hole gets the maximum value at the point where specific heat diverges and the second-order phase transition occurs at the same point. We find that the smaller nonsingular black holes are stable due to positive heat capacity and negative free energy. We explicitly trace the relations between the black hole shadow and the critical behavior of charged EGB $AdS$ regular black hole in the extended phase space.

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arXiv2022

Renyi Holographic Dark Energy models in Teleparallel gravity

In this paper, we have investigated the physical behavior of cosmological models in the framework of modified Teleparallel gravity. This model is established using a Renyi holographic ``dark energy model (RHDE) with a Hubble cutoff. Here we have considered a homogeneous and isotropic Friedman universe filled with perfect `fluid. The physical parameters are derived for the present model in Compliances with 43 observational Hubble data sets (OHD). The equation of state (EoS) parameter in terms of $H(z)$ describes a the transition of the universe between phantom and non-phantom phases in the context of $f(T)$ gravity. Our model shows the violation of strong energy condition (SEC) and the weak energy condition (WEC) over the accelerated phantom regime. We also observed that these models occupy freezing regions through $ω_{D} -ω_{D}^{'}$ plane. Consequently, our Renyi HDE model is supported to the consequences of general relativity in the framework of $f(T)$ modified gravity.

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arXiv2022

Corrected holographic dark energy with power-law entropy and Hubble Horizon cut-off in FRW Universe

In the present work, we investigate the power-law entropy corrected holographic dark energy (PLECHDE) model with Hubble horizon cutoff. We use 46 observational Hubble data points in the redshift range $0 \leq z \leq 2.36$ to determine the present Hubble constant $H_0$ and the model parameter $n$. It represents a phase transition of the universe from deceleration to acceleration and has the transition point at $z_t = 0.71165$. We investigate the observational constraints on the model and calculate some relevant cosmological parameters. We examine the model's validity by drawing state-finder parameters that yield the result compatible with the modern observational data. The model's physical and geometrical characteristics are also explored, and they are shown to match well with current observations of observational Hubble data (OHD) and the latest joint light curves(JLA) datasets.

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arXiv2022

Cosmographic analysis of a closed bouncing universe with the varying cosmological constant in $f(R,T)$ gravity

Modeling of matter bounce in $f(R,T)$ gravity has been presented with no violation of the null energy condition. Only a closed universe with negative pressure is allowed in good agreement with some recent observations which favor a universe with positive curvature. Our results agree with some recent works in which a combination of positive curvature and vacuum energy leads to non-singular bounces with no violation of the null energy condition. The stability of the model has been discussed. The cosmographic parameters are developed for the derived model to explain the accelerated expansion of the universe.

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arXiv2022

Bianchi type-V Transitioning model in Brans-Dicke theory with Observational Constraint

In this paper, we have examined the viability of the Bianchi type-V universe in Brans-Dicke (BD) theory of gravitation. We have discussed the interacting and non-interacting scenarios between dark matter (DM) and dark energy (DE) of the derived universe within the framework of BD theory. CCA technique has been applied to constrain the model parameters using 46 values of observational Hubble data (OHD), Pantheon data (the latest compilation of SNIa with 40 binned in the redshift range $0.014 \leq z \leq 1.62)$ and their combined datasets. We establish an exact solution of the field equations to derive the dynamics of the derived universe and the obtained results are found to agree with the observations. We also noted a distinctive change in the sign of the deceleration parameter from positive to negative, as well as the presence of a transition red-shift exists. Using various observational data points, the evolution trajectories for $(r~- s)$ diagnostic planes are shown to understand the geometrical behavior of the Bianchi-V model. Some physical properties of the universe are also discussed. It's also worth noting that the conclusions of the cosmological parameter are consistent with modern observational data.

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arXiv2022

An Axially Symmetric Transitioning models with Observational Constraints

In this study, we have demonstrated the expansion history of an axially symmetric Bianchi type-I model of the universe. Our model as of now presents an accelerating universe, which had been in the decelerating phase in the past. Roles of the two crucial Hubble~$H(z)$ and deceleration~$q(z)$ parameters are examined. The energy parameters of the universe are estimated with the help of the latest observational Hubble data (46-data points) and Pantheon data (the latest compilation of SNIa with 40 binned in the redshift range $0.014 \leq z \leq 1.62)$. We also discuss the stability analysis of the model by state finder diagnosis. The analysis reveals that in late time, the model is a quintessence type and points towards the $Λ$CDM model. Our developed model agrees with observational findings in a proper way. We have discussed some of the physical aspects of the model.

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