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G. P. Singh

Publications and source records attributed to G. P. Singh.

At least 19 recordsLinked to original sources
arXiv2026

A new parametric study of $f(T)$ teleparallel gravity with generalized Chaplygin gas: Confronting observational data

In this paper, we investigate the cosmological dynamics of a modified gravity framework based on the function $f(T)=β(-T)^{1/2}+γ(-T)$, where $T$ denotes the torsion scalar. The matter sector is modeled using the Generalized Chaplygin Gas (GCG) with the equation of state $p=-\frac{\mathcal{A}}{ρ^η}$, allowing the model to describe the evolution from an early-time matter-like phase to a late-time accelerated universe. By deriving an analytical expression for the Hubble parameter $H(z)$, we perform parameter estimation using Bayesian statistical techniques based on the $χ^{2}$-minimization method with the Cosmic Chronometer (CC) and joint (CC+Pantheon) observational datasets. The deceleration parameter exhibits a transition from deceleration to acceleration, while the present-day value indicates the current accelerated expansion. The model yields a present-day EoS parameter consistent with dark-energy-like behavior, while the energy conditions indicate that the NEC and DEC are satisfied and the SEC is violated at late times. The $ω-ω'$ plane shows a freezing quintessence behavior, approaching the $Λ$CDM-like point $(ω,ω')=(-1,0)$, while the cosmographic analysis offers additional insight into the evolution of the cosmic expansion. The estimated age of the universe is also consistent with current observational bounds. These results demonstrate that the GCG scenario within $f(T)$ teleparallel gravity provides a viable and observationally consistent framework for explaining the late-time accelerated expansion of the universe.

gr-qc↗
arXiv2026

Bianchi Type I Space -Time Geometry of the Universe with Time Dependent G and $Λ$ Within the Framework of General Relativity: Observational Aspects

Inspired by the latest progress in the hunt of acceptable cosmological model of the universe, present paper is devoted to explore a mathematical model of the universe having initial anisotropy and with accelerated evolution that attains isotropic character. We have considered a widely accepted anisotropic Bianchi type I space-time geometry of the universe to explore a physically viable model. To find an acceptable model, we adopted a hyperbolic form for the scale factor as $ a(t)= \left( sinh bt \right)^{\frac{1}{n}} $ and a relation $ Λ=Λ_0 \frac{\ddot{a}}{a}$. The model parameters are constrained by $ χ^2$ minimization techniques. Using 35 CC measurements we obtain present day expansion rate $H_0= 65.715 Km/S/Mpc$ and the value of $ n= 1.3024$. Further to estimate the local uncertainties of the best fit parameter, we calculate covariance from the Jacobin of the normalized residuals. The corresponding 1 $σ$ uncertainties are $ H_0=65.715 \pm 2.392 Km/S/Mpc$ and $n= 1.3024 \pm 0.0842$. The physical and dynamical behaviour of present model has been discussed by a graphical representation of cosmological parameters. The observational constraints on the expansion history are found to be consistent with a present accelerated phase and a transition from deceleration to acceleration at an intermediate redshift. The corresponding evolution of the derived cosmological quantities is also investigated within the adopted model.

physics.gen-ph↗
arXiv2026

Probing cosmic dynamics in $f(T)$ teleparallel gravity: Constraints from logarithmic and log-periodic deceleration ansatzes

In this study, we probe the cosmological evolution of the universe within the framework of modified teleparallel gravity by considering a power-law form of the function $f(T)=α(-T)^{n}$. To characterize the expansion dynamics, we employ logarithmic and log-periodic parametrizations of the deceleration parameter. These specific parametrizations provide a flexible and well-structured description of the cosmic expansion history across different cosmological epochs. The corresponding Hubble parameter is obtained as a function of redshift, facilitating a systematic investigation of the background dynamics. The model parameters are constrained using cosmic chronometer (CC) and joint (CC+Pantheon) datasets through a Bayesian analysis based on the $χ^{2}$-minimization approach. The evolution of key cosmological quantities, including the deceleration parameter, energy density, pressure, equation of state parameter and energy conditions, is examined in detail. The geometrical diagnostics indicate a clear departure from the standard cosmological constant behavior, pointing toward a dynamically evolving dark energy scenario. Further, the proposed models remain thermodynamically consistent and the estimated age of the universe is found to be compatible with observational constraints, thereby reinforcing the robustness and viability of the framework.

gr-qc↗
arXiv2026

Reconstructing the cosmic expansion in $f(R, L_{m})$ gravity via parametrized Hubble function constraints

We probe the cosmic expansion scenario within the framework of $f(R, L_{m})$ gravity by employing a well-motivated functional form of $f(R, L_{m}) = \frac{R}{2} + L_{m}^λ$. Specifically, we introduce three novel cosmological models formulated in terms of the redshift-dependent Hubble parameter $H(z)$, offering deeper insights into the underlying cosmic dynamics. The models are further utilized to investigate the expansion history of the universe and the evolution of several cosmological parameters. By using the Bayesian methods based on the $χ^{2}$-minimization technique, the median values of the model parameters are determined for the cosmic chronometer (CC) and joint (CC+Pantheon) datasets. A comprehensive study of the deceleration parameter, energy density, pressure and the equation of state parameter is carried out to understand the universe's evolution. Additionally, the validity of the energy conditions and the behavior of the statefinder diagnostic are thoroughly examined. Finally, the thermodynamic viability of the models is confirmed through the evolution of temperature and entropy density, and the estimated age of the universe further exemplifies good agreement with late-time astronomical observations.

gr-qc↗
arXiv2026

The $f(Q, T)$ gravity and affine EoS: observational aspects

In this paper, we investigate the cosmic expansion scenarios within the framework of $f(Q,T)$ gravity by using the affine equation of state (EoS) parameter. Specifically, we consider the linear form $f(Q,T)=Q+βT$, where $β$ is a free model parameter. We use Bayesian statistical methods, specifically the $χ^2$ minimization technique to constrain the model parameters using Cosmic Chronometer (CC), Pantheon+SH0ES and DESI BAO data. We further analyze the characteristics of the derived cosmological model. A comprehensive study of energy density, pressure, equation of state parameter and cosmographic parameters are carried out to understand the evolution of the Universe in this model. The determination of present age of the universe for this model is within $1σ$ with Planck results.

gr-qc↗
arXiv2026

Transiently accelerating cosmological model with Gong-Zhang parametrization in $f(T)$ teleparallel gravity

We present the cosmic expansion scenario in the framework of $f(T)$ gravity by employing a dark energy equation of state (EoS) parameter. Specifically, we proceed with the power-law form of the function $f(T) = α$$(-T)^{n}$, in conjunction with the Gong-Zhang parametrization of the dark energy EoS. We derive the expansion rate in terms of the redshift for the considered model, providing deeper insights into the underlying cosmic dynamics. The model is further utilized to explore the expansion history of the universe and the evolution of several cosmological parameters. By using the Bayesian methods based on the $χ^{2}$-minimization technique, the median values of the model parameters are determined for the cosmic chronometer (CC) and joint (CC+Pantheon) datasets. The evolution of the deceleration parameter, energy density, pressure, EoS parameter and the energy conditions for dark energy is analyzed in detail. The model captures the observed acceleration as a transient phenomenon, followed by future deceleration. Additionally, the nature of both geometrical and dynamical diagnostics robustly indicates a quintessence-like behavior at the present epoch. Finally, the thermodynamic viability of the model is confirmed through the generalized second law of thermodynamics and the estimated age of the universe further supports the model's compatibility with astronomical observations.

gr-qc↗
arXiv2026

Revisiting $f(T)$ Teleparallel Gravity with a Parametrized Hubble Parameter and Observational Constraints

In this paper, the dynamical behavior of the accelerated expansion of the universe is studied within the framework of $f(T)$ gravity by considering a well-motivated functional form of $f(T)$. A specific form of the Hubble parameter is assumed, which under two different cases, leads to two distinct cosmological models expressed in terms of the redshift parameter $H(z)$, providing insights into cosmic dynamics. These models are employed to explore the expansion history of the universe and the evolution of several cosmological parameters. Using Bayesian statistical techniques based on the $χ^{2}$-minimization method, the median values of the model parameters are determined for both the cosmic chronometer (CC) and the joint (CC + Pantheon) datasets. The evolution of the deceleration parameter, energy density, pressure and the equation of state parameter for dark energy is analyzed. Additionally, the validity of the energy conditions and the nature of the statefinder diagnostic are examined. The present age of the universe is also estimated for the proposed models.

gr-qc↗
arXiv2026

The $f(Q)$ gravity and affine EoS: Compatibility and observational constraints

We study the cosmological implications of barotropic fluid satisfying affine equation of state (EoS) in the General relativity and $f(Q)$ gravity framework. We describe the impact of affine EoS on the cosmic evolution in the model and derive the observational constraints on the model parameters. The models of General relativity and $f(Q)$ gravity may unify the scenario in which the universe transits from the decelerated expansion into the accelerated expansion. The model parameters are constrained by the Bayesian analysis based on $χ^{2}$ minimization technique with the observational data of the Cosmic chronometer and Supernovae type Ia. The affine EoS model in the General Relativity possess quintessence kind of dark energy while it possess phantom kind of dark energy in the $f(Q)$ gravity. The present day values of the cosmological parameters along with the current age of the universe are compatible with the observations. We also probe the possibility of setting up the solution of General relativity model into the $f(Q)$ gravity.

gr-qc↗
arXiv2026

Dynamical constraints on variable vacuum energy in Brans-Dicke theory

In this research work, we investigate the late-time accelerated expansion of the universe within the framework of Brans-Dicke theory by considering dynamical vacuum energy models with a time-varying cosmological constant. Two vacuum energy models are studied, namely the hybrid vacuum law $Λ(t)=αH^{2}+β\dot{H}$ and the power vacuum law $Λ(H)=α_{1}H^{n}$, where $α$, $β$, $α_{1}$ and $n$ are free parameters. We derive analytical solutions for the Hubble parameter and other relevant cosmological quantities. The evolution of the deceleration parameter, the effective equation of state parameter, the cosmographic parameters, the behaviour of Om($\mathit{z}$) diagnostics and the present age of the universe are examined. Furthermore, the analysis of the $ω_{\rm eff}-ω'_{\rm eff}$ plane shows that the model evolves in the freezing region and the thermodynamic analysis confirms that the generalized second law of thermodynamics is satisfied within the power vacuum law model.

gr-qc↗
arXiv2025

Cosmological model with Gong-Zong Parametrization in $f(R,L_m)$ gravity

We present the cosmic expansion scenarios in the $f(R, L_m)$ gravity studied by using the dark energy equation of state (EoS) parameters. We proceed with the specific form of $f(R, L_m)$ gravity termed as $f(R, L_m)=\frac{R}{2}+L_{m}^α$. We derive the expansion rate in terms of the red-shift for two different forms of EoS parameter. In first model, EoS parameter varies inversely with the redshift and in second model, it involves the exponential form with the redshift. By using the Bayesian methods based on the $χ^{2}$-minimization technique, the median values of model parameters are determined for the cosmic chronometer(CC) and Joint (CC+Pantheon) data sets. The behavior of fundamental cosmological parameters such as the deceleration parameter, energy density and pressure are thoroughly examined. Additionally, the nature of Statefinder diagnostics and the present age of universe exemplifies the compatibility with the late-time astronomical observations.

gr-qc↗
arXiv2025

Accelerated expansion of the universe model with parametrization of $q(z)$ in $f(R,L_m)$ theory of gravity

In this research work, we explore the late-time accelerated expansion of the universe within the framework of modified gravity, specifically $f(R, L_m)$ theory, by considering two non-linear models: $f(R, L_{m}) = \frac{R}{2}+(1+ηR) L_{m}$ and $f(R, L_{m}) = \frac{R}{2}+ L_{m}^η$, where $η$ is a free parameter. Adopting a parametric form of the deceleration parameter $q(z)$, we derive a quadratic expression for the normalized Hubble parameter. By use of Bayesian statistical analysis with the $χ^{2}$-minimization approach, we determine the median values of the model parameters for both the cosmic chronometer (CC) and the joint (CC+Pantheon) dataset. Furthermore, we examine the fundamental cosmological parameters: energy density, pressure, the equation of state (EoS) parameter and energy conditions. The cosmographic parameters are thoroughly analyzed and the present age of the universe is estimated based on this model.

gr-qc↗
arXiv2025

Late-time dynamics of dark energy EoS in symmetric teleparallel gravity

In the symmetric teleparallel gravity framework, we study the cosmic dynamics of the universe with dark energy equation of state (EoS) parameter having non-linear forms. The non-metricity scalar induced by the dark energy EoS parameter evolves with time and, explains the physically reasonable transiting universe evolution in a consistent way. A comparative study has been presented to describe the ability of these models to fit the observational data. By using the Bayesian methods, we constrain the model parameters with the supernovae Ia (SneIa) and expansion rate data. We show that the expansion rate solutions may consistently describe the universe evolution based on cosmological indicators such as the effective EoS parameter, energy density, pressure, current age and the statefinder diagnostic. One may either have the quintom scenario or the future deceleration in these models subjected to the observational constraints.

gr-qc↗
arXiv2024

A generalized $Λ$CDM model with parameterized Hubble parameter in particle creation, viscous and $f(R)$ model framework

In this study, we construct a theoretical framework based on the generalized Hubble parameter form which may arise within the particle creation, viscous and $f(R)$ gravity theory. The Hubble parameter is scrutinized for its compatibility with the observational data relevant to the late-time universe. By using Bayesian statistical techniques based on $χ^{2}$ minimization method, we determine model parameters's best fit values for the cosmic chronometer and supernovae Pantheon datasets. For the best fit values, the cosmographic and physical parameters are analyzed to understand the cosmic dynamics in model. We also analyze the model section criterion in comparison to the $Λ$ cold dark matter model.

gr-qc↗
arXiv2024

Cosmological model with linear equation of state parameter in f(R, Lm) gravity

In this paper, we examine the universe's expansion in $ f(R, L_{m}) $ gravity for a particular form of $ f(R, L_{m})=\frac{R}{2}+L_{m}^{n}$. The field equations for flat FLRW metric with matter Lagrangian $ L_{m}=ρ$ are derive. Hubble parameter in terms of red-shift$(z)$ are derived using the linear form of Equation of State (EoS) parameter $ ω=w_{0}+w_{1}z $. By using Bayesian statistical techniques based on $ χ^{2}$-minimization technique, we have obtained the best fit values of the model parameters of this model for cosmic chronometer and supernovae Pantheon datasets. The evolution of the equation of state parameter$(ω)$, energy density $ (ρ) $, pressure $\mathit{(p)}$ cosmographic parameters, and the impact of the energy conditions with best-fit values of the model parameters are all thoroughly examined. We have also analyze Om diagnostic's behavior and determine the present age of universe for this model.

gr-qc↗
arXiv2022

Bianchi-I cosmology with generalized Chaplygin gas and periodic deceleration parameter

This manuscript investigate the dark energy Bianchi type-I cosmological models in presence of generalized Chaplygin gas, variable gravitational and cosmological constants. In this manuscript, exact solutions of Einstein field equations are obtained under the assumption of time periodic varying deceleration parameter. The physical and dynamical behaviors of the models have been discussed with the help of graphical representations. Also we have discussed the stability and physical acceptability of the obtained solutions

gr-qc↗
arXiv2019

Variable Chaplygin gas cosmologies in f(R, T) gravity with particle creation

A flat FLRW cosmological model with perfect fluid comprising of variable Chaplygin gas has been studied in context of f(R; T) gravity with particle creation. The considered scale factors describe the accelerated expansion of universe due to the effective negative pressure produced during evolution of universe. The role of particle creation pressure on the cosmological parameters have been discussed in detail. By considering well accepted values of free parameters, the late time expansion of the universe with energy conditions have also been studied. The state-finder diagnostic for the considered cases have been studied and the evolution of source function with time have suggested almost constant particle production at late times.

gr-qc↗
arXiv2017

LRS Bianchi type-I cosmological model with constant deceleration parameter in $f(R,T)$ 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.

gr-qc↗