arXiv subjects

Parbati Sahoo

Publications and source records attributed to Parbati Sahoo.

17 recordsLinked to original sources

arXiv2026

A Bayesian Statistical Study of Bianchi Type-I Universe in $f(R,T^\psi)$ Modified Gravity

We have examined the cosmological actions of LRS (Locally Rationally Symmetric) Bianchi type-I universe model in $f(R,T^\psi)$ gravity. For this, we have estimated the Hubble parameter, the effective equation of state parameter ($\omega^{eff}$), and the potential of the scalar field as a function of time using equation $H = W(\psi)$. The graphical representation of the potential function $V(\psi)$ with respect to cosmic time t is described. This study explores the dynamical properties of a Bianchi Type-I universe by utilizing Bayesian statistical techniques to constrain the model parameters and evaluate the viability of anisotropic cosmology under extended matter-geometry couplings. Also, we have applied the Markov Chain Monte Carlo (MCMC) mechanism on the derived $H(z)$ model by using observational Hubble data (OHD), the Baryon Acoustic Oscillation (BAO) dataset, and the Pantheon dataset. From the confidence-level contours and best-fit parameter values obtained, along with the corresponding reduced $\chi^{2}$, it is evident that the model aligns strongly with observational data, demonstrating statistical stability and consistency in describing late-time cosmic acceleration. Likewise, the error analyses presented in this research, including a comparison between the $\Lambda$CDM cosmology and the reconstructed $H(z)$ model, confirm the model's compatibility with current observations by yielding a reliable and accurate account of the universe's expansion history.

gr-qc↗

arXiv2025

Study of Accelerated Expansion of Universe in the framework of $f (R, T )$ Gravity

This thesis explores the late-time cosmic acceleration within the framework of $f(R,T)$ gravity, a general relativity modification that incorporates the Ricci scalar $R$ and the trace of the energy-momentum tensor $T$. Motivated by observational evidence for the universe's accelerated expansion and the limitations of Einstein's theory in explaining dark energy, we study exact cosmological solutions using various parametrizations of the deceleration parameter. The analysis includes isotropic and anisotropic models such as Bianchi type I universes with string fluid, bulk viscous matter, and magnetized strange quark matter. Several forms of time-varying deceleration parameters are employed to understand the dynamical behavior of the universe. We also examine finite-time singularities like the Big Rip and discuss their occurrence in both anisotropic and FLRW backgrounds. In addition, the thesis investigates higher-order curvature corrections and geometric modifications, including wormhole solutions, within the $f(R,T)$ formalism. Energy conditions are analyzed to assess the physical plausibility of these models. The overall work aims to provide a coherent and viable description of the universe's evolution under modified gravity theories.

gr-qc↗

arXiv2021

Periodic cosmic evolution in $f(Q)$ gravity formalism

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.

gr-qc↗

arXiv2020

Traversable wormholes in the traceless $f(R,T)$ gravity

We present a traversable wormhole solution using the traceless $f(R,T)$ theory of gravity. In the $f(R,T)$ gravity, the Ricci scalar $R$ in the Einstein-Hilbert action is replaced by a function of $R$ and trace of the energy momentum tensor $T$. The traceless version of the $f(R,T)$ gravity gives rise to a possible wormhole geometry without need for "exotic matter", which violates the principle of causality. Using a physically plausible ansatz for the wormhole's shape function, the traceless field equations lead to compliance with the weak energy condition at very well defined intervals of the coupling constant $\lambda$ in the $f(R,T)=R+2\lambda T$ form. Our solution leads to other well-behaved energy conditions considering some possible values of the parameter $\omega$ in the equation of state $p_r=\omega \rho$, with $p_r$ being the radial pressure and $\rho $ the density. The energy conditions are obeyed in the ranges $\lambda < -4\pi$ and $\omega > -1$. Through the calculation of the Volume Integral Quantifier, one sees that this wormholes can be traversable and respect the causality, since the amount of exotic matter in its interior can be arbitrarily small.

gr-qc↗

arXiv2020

Mixed fluid cosmological model in $f(R,T)$ gravity

We construct Locally Rotationally Symmetric (LRS) Bianchi type-I cosmological model in $f(R,T)$ theory of gravity when the source of gravitation is the mixture of barotropic fluid and dark energy (DE) by employing a time varying deceleration parameter (DP). We observe through the behavior of the state finder parameters $(r, s)$ that our model begins from the Einstein static era and goes to $\Lambda$CDM era. The EoS parameter($\omega_d$) for DE varies from phantom ($\omega<-1$) phase to quintessence ($\omega >-1$) phase which is consistent with the observational results. It is found that the discussed model can reproduce the current accelerating phase of expansion of the universe.

physics.gen-ph↗

arXiv2019

Wormhole model with a hybrid shape function in f(R,T) gravity

In the present article we propose a new hybrid shape function for wormhole (WH)s in the modified $f(R,T)$ gravity. The proposed shape function satisfied the conditions of WH geometry. Geometrical behavior of WH solutions are discussed in both anisotropic and isotropic cases respectively. Also, the stability of this model is obtained by determining the equilibrium condition. The radial null energy condition and weak energy condition are validated in the proposed shape function indicating the absence of exotic matter in modified $f(R,T)$ gravity.

gr-qc↗

arXiv2019

Bouncing scenario in $f(R,T)$ gravity

The present manuscript presents modeling of matter bounce in the framework of $f(R,T)$ gravity where $f(R,T) = R + 2 \lambda T$. We start by defining a parametrization of scale factor which is non-vanishing. The geometrical parameters such as the Hubble parameter and deceleration parameter are derived, from which expressions of pressure, density and Equation of State (EoS) parameter and a qualitative understanding of the initial conditions of the universe at the bounce are ascertained. We found that the initial conditions of the universe are finite owing to the non-vanishing nature of the scale factor thus eliminates the initial singularity problem. Furthermore, we show the violation of energy conditions near the bouncing region and analyzed the stability of our model with respect to linear homogeneous perturbations in Friedmann-Lema\^tre-Robertson-Walker (FLRW) spacetime. We found that our model and hence matter bounce scenarios in general are highly unstable at the bounce in the framework of $f(R,T)$ gravity but the perturbations decay out rapidly away from the bounce safeguarding its stability at late times.

gr-qc↗

arXiv2019

Phantom fluid wormhole in $f(R,T)$ gravity

Wormholes (WHs) are considered as hypothetical shortcuts or tunnels in spacetime. In general relativity (GR), the fundamental ingredient of WH geometry is the presence of exotic matter at the throat, which is responsible for the violation of null energy condition (NEC). However, the modified gravity theories has shown to be able to provide WH solutions satisfying energy conditions (ECs). In this paper, we study the static spherically symmetric WH solutions in modified $f(R,T)$ gravity for a phantom fluid case. The exact solutions of this model are obtained through the equation of state (EoS), $p=\omega \rho$, associated with phantom dark energy (DE) $\omega<-1$. We find the existence of spherically symmetric WH solution supported by phantom energy distribution. The shape function of the WH is obtained in this model obeys all the WH metric conditions. In modified gravity scenario the phantom fluid WH violates the NEC in radial case, unlike in the tangential case. Furthermore, using the "volume integral quantifier" (VIQ) method, the total amount of EC violating matter in spacetime is discussed briefly.

gr-qc↗

arXiv2019

Phantom energy dominated universe as a transient stage in $f(R)$ cosmology

The $f(R)$ theories of gravity are the most popular, simple and well succeeded extension of Einstein's General Relativity. They can account for some observational issues of standard cosmology with no need for evoking the dark sector of the universe. In the present letter we will investigate LRS Bianchi type-I space-time in $f(R)$ gravity theory within the phantom energy dominated era. We show that in this formalism the phantom energy dominated universe is a transient stage and in the further stage of the universe dynamics, it is dominated, once again, by dark energy. Such an important feature is obtained from the model, rather than imposed to it, and may have a relation to loop quantum cosmology.

gr-qc↗

arXiv2018

$f(R,T)=f(R)+λT$ gravity models as alternatives to cosmic acceleration

This article presents cosmological models that arise in a subclass of $f(R,T)=f(R)+f(T)$ gravity models, with different $f(R)$ functions and fixed $T$-dependence. That is, the gravitational lagrangian is considered as $f(R,T)=f(R)+λT$, with constant $λ$. Here $R$ and $T$ represent the Ricci scalar and trace of the stress-energy tensor, respectively. The modified gravitational field equations are obtained through the metric formalism for the Friedmann-Lemaître-Robertson-Walker metric with signature $(+,-,-,-)$. We work with $f(R)=R+αR^2-\frac{μ^4}{R}$, $f(R)=R+k\ln(γR)$ and $f(R)=R+me^{[-nR]}$, with $α, μ, k, γ, m$ and $n$ all free parameters, which lead to three different cosmological models for our Universe. For the choice of $λ=0$, this reduces to widely discussed $f(R)$ gravity models. This manuscript clearly describes the effects of adding the trace of the energy-momentum tensor in the $f(R)$ lagrangian. The exact solution of the modified field equations are obtained under the hybrid expansion law. Also we present the Om diagnostic analysis for the discussed models.

gr-qc↗

arXiv2018

A periodic varying deceleration parameter in $f(R,T)$ gravity

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 have also explored the obvious violation of energy momentum conservation in $f(R,T)$ gravity. The periodic behaviour of energy conditions for the model are also discussed with a wide range of the free parameters.

gr-qc↗

arXiv2018

Phantom fluid supporting traversable wormholes in alternative gravity with extra material terms

Wormholes are tunnels connecting different regions in space-time. They were obtained originally as a solution for Einstein's General Relativity theory and according to this theory they need to be filled by an exotic kind of anisotropic matter. In the present sense, by "exotic matter" we mean matter that does not satisfy the energy conditions. In this article we propose the modelling of wormholes within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, named redshift and shape functions, and yield the wormholes to be filled by a phantom fluid, that is, a fluid with equation of state parameter $ω<-1$. In possession of the solutions for the wormhole material content, we also apply the energy conditions to them. The features of those are carefully discussed.

gr-qc↗

arXiv2018

Wormholes in $R^2$-gravity within the $f(R,T)$ formalism

We propose, as a novelty in the literature, the modelling of wormholes within the particular case of the $f(R,T)$ gravity, namely $f(R,T)=R+αR^{2}+λT$, with $R$ and $T$ being the Ricci scalar and trace of the energy-momentum tensor, respectively, while $α$ and $λ$ are constants. Although such a functional form application can be found in the literature, those concern to compact astrophysical objects, such that no wormhole analysis has been done so far. The quadratic geometric and linear material corrections of this theory make the matter content of the wormhole to remarkably be able to obey the energy conditions.

gr-qc↗

arXiv2017

LRS Bianchi type-I bulk viscous cosmological models in $f(R,T)$ gravity

We have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model in $f(R,T)$ gravity ($R$ is the Ricci scalar and $T$ is the trace of the stress energy tensor) with Bulk viscous fluid as matter content. The model is constructed for the linear form $f(R,T)=R+2f(T)$. The exact solution of field equations is obtained by using a time varying deceleration parameter $q$ for a suitable choice of the function $f(T)$. In this work, the bulk viscous pressure $\bar{p}$ is found to be negative and energy density $ρ$ is found to be positive. The obtained model is anisotropic, accelerating and compatible with the results of astronomical observations. Also, some important features of physical parameters of this model have been discussed.

gr-qc↗

arXiv2017

Magnetized strange quark matter in $f(R,T)$ gravity with bilinear and special form of time varying deceleration parameter

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 constant $α$. Second one is the special form of the DP as $q=-1+\fracβ{1+a^β}$. From obtained results, we could say that in the early universe the magnetic flux has more effects and it gradually reducing its effects in later. For $t\rightarrow \infty$, we get $p\rightarrow -B_c$ and $ρ\rightarrow B_c$. So the strange quark matter along with magnetic epoch gives an idea of accelerated expansion of the universe as per the observations of the type Ia Supernovae.

gr-qc↗

arXiv2017

Magnetized strange quark model with Big Rip singularity in $f(R,T)$ gravity

LRS (Locally Rotationally symmetric) Bianchi type-I magnetized strange quark matter cosmological model have been studied based on $f(R,T)$ gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model start with big bang and ends with a Big Rip. The transition of deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. in 2017. The well known Hubble parameter $H(z)$ and distance modulus $μ(z)$ are discussed with redshift.

physics.gen-ph↗

arXiv2017

Anisotropic cosmological models in $f(R,T)$ gravity with variable deceleration parameter

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 universe. We have explored the nature of WEC, DEC, SEC and energy density for both the cases. We have found that both the models, with bulk viscosity matter component, show an acceleration of the universe. We have also shown that the cosmic jerk parameter is compatible with the three kinematical data sets.

gr-qc↗