arXiv subjects

Romanshu Garg

Publications and source records attributed to Romanshu Garg.

9 recordsLinked to original sources

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

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 Dynamics of Accelerating Model in $f(T)$ Gravity with Special Forms of Deceleration Parameter

In this paper, the dynamical behavior of the accelerated expansion of the universe is discussed within the framework of $f(T)$ gravity, considering power law functional form of $ f(T)=α(-T)^{n}$. Two distinct redshift-dependent parameterization of the deceleration parameter such as $q(z)=q_{0}+ q_{1}\left(\frac{ \ln(N+z)}{z+1}-\ln N \right)$ and $ q(z)=\frac{1}{2}+ \frac{q_{1}z+ q_{2}}{(1+z)^2} $ are considered. We have derived the Hubble parameter in terms of redshift and discussed its effect on other cosmological parameters. Using Bayesian statistical analysis and $χ^2$-minimization, the median values of the model parameters for both the cosmic chronometer(CC) and the joint(CC + Pantheon) dataset have been determined. Further, energy density, pressure, the equation of state for Dark Energy, Energy condition and statefinder diagnostics are analyzed. The current age of the universe is also computed for these models.

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↗

arXiv2025

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 $\chi^{2}$ 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↗

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 $f(R, L_m)=\frac{R}{2}+L_{m}^{\alpha}$. 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 $\chi^{2}$-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↗

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↗