arXiv subjects

P. K. Sahoo

Publications and source records attributed to P. K. Sahoo.

At least 127 records · Page 7Linked to original sources

arXiv2022

Crossing phantom divide in $f(Q)$ gravity

We investigate the possibility of crossing a phantom divide line in the extension of symmetric teleparallel gravity or the $f(Q)$ gravity, where $Q$ is the non-metricity. We study the cosmic evolution of the effective equation of state parameter for dark energy considering exponential, logarithmic, and combined $f(Q)$ theories. Moreover, the exponential model behaves like the $Λ$CDM at high redshifts before deviating to $ω_{eff}<-1$ or $ω_{eff}>-1$, respectively, depending on the value of model parameter. It also approaches a de-sitter phase asymptotically. However, the crossing of the phantom divide line, i.e., $ω= -1$, is realized in the combined $f(Q)$ theory. Furthermore, statefinder diagnostics are studied in order to differentiate between several dark energy models. To ensure the three model's stability, we employ the stability analysis using linear perturbations. We demonstrate how to reassemble $f(Q)$ via a numerical inversion approach based on existing observational constraints on cosmographic parameters and the potential of bridging the phantom divide in the resulting model. It explicitly demonstrates that future crossings of the phantom dividing line are a generic feature of feasible $f(Q)$ gravity models.

gr-qc↗

arXiv2022

Probing the existence of the ZTF Casimir wormholes in the framework of $f(\mathcal{R})$ gravity

For the spherically symmetric static traversable wormholes, supported by the Casimir energy in $f(\mathcal{R})=\mathcal{R}+α\mathcal{R}^2$ Quadratic, $f(\mathcal{R})=f_0 \mathcal{R}^n$ power-law Modified Gravity (MOG) theories we investigate energy conditions and dynamical stability of the wormhole solutions. Especially, we study Zero Tidal Forces (ZTF) Casimir WH's with anisotropic fluid located at the throat. By using the Casimir energy density and modified Einstein Field Equations (EFE's) we derived suitable shape functions for each modified gravity of our consideration. The stability of Casimir traversable wormholes in different modified gravity theories is also analyzed in our paper with a modified Tolman-Oppenheimer-Voklov (MTOV) equation. Besides, we have numerically solved MTOV and derived hydrodynamical, anisotropic and extra forces, that is present due to the non-conserved stress-energy tensor. Moreover, other fundamental quantities, such as Volume Integral Quantifier and total gravitational energy were derived.

physics.gen-ph↗

arXiv2022

Accelerating expansion of the universe in modified symmetric teleparallel gravity

The fundamental nature and origin of dark energy are one of the premier mysteries of theoretical physics. In General Relativity Theory, the cosmological constant $Λ$ is the simplest explanation for dark energy. On the other hand, the cosmological constant $Λ$ suffers from a delicate issue so-called fine-tuning problem. This motivates one to modify the spacetime geometry of Einstein's GR. The $f(Q)$ gravity is a recently proposed modified theory of gravity in which the non-metricity scalar $Q$ drives the gravitational interaction. In this article, we consider a linear $f(Q)$ model, specifically $f(Q)=αQ + β$, where $α$ and $β$ are free parameters. Then we estimate the best fit values of model parameters that would be in agreement with the recent observational data sets. We use 57 points of the updated $H(z)$ data sets, 6 points of the BAO data sets, and 1048 points from the Pantheon supernovae samples. We apply the Bayesian analysis and likelihood function along with the Markov Chain Monte Carlo (MCMC) method. Further, we analyse the physical behaviour of cosmological parameters such as density, deceleration, and the EoS parameters corresponding to the constraint values of the model parameters. The evolution of deceleration parameter predicts a transition from decelerated to accelerated phases of the universe. Further, the evolution of equation of state parameter depicts quintessence type behaviour of the dark energy fluid part. We found that our $f(Q)$ cosmological model can effectively describe the late time cosmic acceleration without invoking any dark energy component in the matter part.

gr-qc↗

arXiv2022

Statefinder Analysis of Symmetric Teleparallel Cosmology

Statefinder diagnostic is a convenient method that can differentiate between the various dark energy models. In this article, we analyze the statefinder parameters in symmetric teleparallel cosmology. The $f(Q)$ gravity theory is an alternative theory to GR, where gravitational interactions attribute to the non-metricity scalar $Q$. In the present work, we consider two $f(Q)$ models which contains a linear and a non-linear form of non-metricity scalar, specifically, $f(Q)=αQ + \fracβ{Q}$ and $f(Q)=αQ + βQ^2$, where $α$ and $β$ are free parameters and then statefinder parameters $(r,s)$ are evaluated. We plot the trajectory of our models in the $r-s$ plane. In addition, we analyze the physical behavior of different cosmological parameters such as density, deceleration, and the EoS parameters. Further, we use Om diagnostic to differentiate the behavior of both $f(Q)$ models. We found that both $f(Q)$ models predicts that the present universe is accelerating due to the dark energy component evolving due to non-metricity. Moreover, model I represents phantom type behavior while model II follows quintessence scenario.

gr-qc↗

arXiv2022

Observational constraints and some toy models in $f(Q)$ gravity with bulk viscous fluid

The standard formulation of general relativity fails to describe some recent interests in the universe. It impels us to go beyond the standard formulation of gravity. The $f(Q)$ gravity theory is an interesting modified theory of gravity, where the gravitational interaction is driven by the nonmetricity $Q$. This study aims to examine the cosmological models with the presence of bulk viscosity effect in the cosmological fluid within the framework of $f(Q)$ gravity. We construct three bulk viscous fluid models, i.e. (i) for the first model, we assuming the Lagrangian $f(Q)$ as linear dependence on $Q$, (ii) for the second model the Lagrangian $f(Q)$ as a polynomial functional form, and (iii) the Lagrangian $f(Q)$ as a logarithmic dependence on $Q$. Furthermore, we use 57 points of Hubble data and 1048 Pantheon dataset to constraint the model parameters. Then, we discuss all the energy conditions for each model, which helps us to test the self-consistency of our models. Finally, we present the profiles of the equation of state parameters to test the models' present status.

gr-qc↗

arXiv2022

Generalised Ellis-Bronnikov Wormholes in $f(R)$ Gravity

In this manuscript, we construct generalized Ellis-Bronnikov wormholes in the context of $f(R)$ modified theories of gravity. We consider that the matter driving the wormhole satisfies the energy conditions so that it is the effective energy-momentum tensor containing the higher-order derivatives of curvature terms that violate the null energy condition. Thus, the gravitational fluid is interpreted by the higher-order derivatives of curvature terms to represent the wormhole geometries and is fundamentally different from its counter representation in general relativity. In particular, we explore the wormhole geometries by presuming various well-known forms of Lagrangian $f(R)$. In addition, for the seek of completeness, we discuss modified Tolman-Oppenheimer-Volkov, volume integral quantifier, and total gravitational energy.

gr-qc↗

arXiv2022

$f(\mathcal{G},T_{αβ}T^{αβ})$ Theory and Complex Cosmological Structure

The basic objective of this investigation is to explore the impact of a novel gravitational modification, specifically, the $f(\mathcal{G}, \mathbf{T}^2)$ (where $\mathbf{T}^2 \equiv T_{αβ}T^{αβ}$, $T^{αβ}$ denotes the stress-energy tensor) model of gravitation, upon the complexity of time-dependent dissipative as well as non-dissipative spherically symmetric celestial structures. To find the complexity factor $(\mathbb{C}_{\mathbf{F}})$ from the generic version of the structural variables, we performed Herrera's scheme for the orthogonal cracking of Riemann tensor. In this endeavor, we are mainly concerned with the issue of relativistic gravitational collapse of the dynamically relativistic spheres fulfilling the presumption of minimal $\mathbb{C}_{\mathbf{F}}$. The incorporation of a less restrictive condition termed as quasi-homologous $(\mathbb{Q}_{\mathbf{H}})$ condition together with the zero $\mathbb{C}_{\mathbf{F}}$, allows us to formulate a range of exact solutions for a particular choice of $f(\mathcal{G}, \mathbf{T}^2)$ model. We find that some of the given exact solutions relax the Darmois junction conditions and describe thin shells by satisfying the Israel conditions, while some exhibit voids by fulfilling the Darmois constraints on both boundary surfaces. Eventually, few expected applications of the provided solutions in the era of modern cosmology are debated.

gr-qc↗

arXiv2022

Kuchowicz gravastars in the braneworld formalism

In the current letter, we study isotropic static spherically symmetric gravastars without charge under the framework of braneworld gravity (dimensionally reduced RS-II braneworld with positive brane tension) using the metric potential of Kuchowicz type (which is physically acceptable, non-singular and stable) in the Mazur-Motolla conjuncture. We derived the Kuchowicz free parameters from the junction conditions assuming Schwarzschild vacuum without cosmological constant. As well, we assume that the interior is filled with Dark Energy (DE-like) fluid, shell with ultrarelativistic stiff fluid. Adopting this conditions, we probed several physical aspects of the gravastars, such as proper length, shell energy and entropy, surface redshift and adiabatic index, interior region mass.

gr-qc↗

arXiv2022

Complete dark energy scenario in $f(Q)$ gravity

In theoretical physics, the fundamental nature and evolution mechanism of dark energy is still an open question. In General Relativity Theory, the simplest explanation for dark energy is the cosmological constant $Λ$. However, the cosmological constant $Λ$ facing a sensitive problem called fine-tunning problem. In the present work, we follow a different approach where the gravitational sector is the responsible candidate for the evolution of dark energy instead of the matter source. The modified symmetric teleparallel gravity or $f(Q)$ gravity is a recently proposed theory of gravity where the gravitational interaction ruled by the non-metricity term $Q$. In this manuscript, we assume a $f(Q)$ model that contains a linear and a non-linear form of non-metricity scalar, particularly $f(Q)=αQ + βQ^n$, where $α$, $β$, and $n$ are free model parameters. Then we find the values of our model parameters that would be in agreement with the observed value of cosmographic parameters. We analyze the behavior of different cosmological parameters like deceleration parameter, density, and the equation of state parameter with the energy conditions for our cosmological model. We found that for higher positive values of $n$ specifically $n \geq 1$, dark energy fluid part evolving due to non-metricity behaves like quintessence type dark energy while for higher negative values of $n$ specifically $n \leq -1$ it follows phantom scenario. Further for $n=0$, our cosmological $f(Q)$ model behaves like $Λ$CDM model. Thus, we conclude that the geometrical generalization of GR can be a viable candidate for the description of origin of the dark energy.

gr-qc↗

arXiv2022

Isotropization of locally rotationally symmetric Bianchi-I universe in $f(Q)$-gravity

Despite having the somewhat successful description of accelerated cosmology, the early evolution of the universe always challenges mankind. Our promising approach lies in a new class of symmetric teleparallel theory of gravity named $f(Q)$, where the non-metricity scalar $Q$ is responsible for the gravitational interaction, which may resolve some of the issues. To study the early evolution of the universe, we presume an anisotropic locally rotationally symmetric (LRS) Bianchi-I spacetime and derive the motion equations. We discuss the profiles of energy density, equation of state and skewness parameter and observe that our models archive anisotropic spatial geometry in the early phase of the universe with a possible presence of anisotropic fluid and as time goes on, even in the presence of an anisotropic fluid, the universe could approach isotropy due to inflation and the anisotropy of the fluid fades away at the same time.

gr-qc↗

arXiv2022

Quantum Gravity Evolution in the Hawking Radiation of a Rotating Regular Hayward Black Hole

In this paper, we study two different phenomena (the Newman-Janis algorithm and the semiclassical Hamilton-Jacobi method) to analyze the Hawking temperature ($T_H$) for massive $4$-dimensional regular Hayward BH with spin parameter. First of all, we compute the rotating regular Hayward black hole solution by taking the Newman-Janis algorithmic rule. We derive the $T_H$ for rotating regular Hayward BH with the help of surface gravity. We have also analyzed the effects of spin parameter $a$ and free parameter $l$ on $T_H$ with the help of graphs. Moreover, we investigate the quantum corrected Hawking temperature ($T'_H$) for rotating regular Hayward black hole. To do so, we utilize the Lagrangian filed equation in the background of GUP within the concept of WKB approximation and semiclassical Hamilton-Jacobi method. The $T'_H$ of rotating regular Hayward BH depends upon correction parameter $β$, BH mass $m$, spin parameter $a$, free parameter $l$ and BH radius $r_+$. We also study the graphical behavior of $T'_H$ versus event horizon $r_+$ for rotating regular Hayward BH and check the influences of quantum gravity parameter $β$, spin parameter $a$ and free parameter $l$ on the stability of corresponding black hole. Moreover, we study the significance's of logarithmic entropy correction for regular rotating Hayward BH.

gr-qc↗

arXiv2022

Energy Conditions in Non-minimally Coupled $f(R,T)$ Gravity

In today's scenario, going beyond Einstein's theory of gravity leads us to some more complete and modified gravity theories. One of them is the $f(R,T)$ gravity in which $ R $ is the Ricci scalar, and $ T $ is the trace of the energy-momentum tensor. Using a well-motivated linear $f(R,T)$ gravity model with a single parameter, we studied the strong energy condition (SEC), the weak energy condition (WEC), the null energy condition (NEC), and the dominant energy condition (DEC) under the simplest non-minimal matter geometry coupling with a perfect fluid distribution. The model parameter is constrained by energy conditions and a single parameter proposed equation of state (EoS), resulting in the compatibility of the $f(R,T)$ models with the accelerated expansion of the universe. It is seen that the EoS parameter illustrate the quintessence phase in a dominated accelerated phase, pinpoint to the cosmological constant yields as a prediction the phantom era. Also, the present values of the cosmological constant and the acceleration of the universe are used to check the viability of our linear $f(R,T)$ model of gravity. It is observed that the positive behavior of DEC and WEC indicates the validation of the model. In contrast, SEC is violating the condition resulting in the accelerated expansion of the universe.

gr-qc↗

arXiv2021

Traversable wormhole inspired by non-commutative geometries in $f(Q)$ gravity with conformal symmetry

This article is based on the study of wormhole geometries in the context of symmetric teleparallel gravity or $f(Q)$ gravity, where $Q$ is the non-metricity scalar, and it is responsible for the gravitational interaction. To discuss the wormhole solutions, we consider spherically symmetric static spacetime metric with anisotropic matter contents under well-known non-commutative distributions known as Gaussian and Lorentzian distributions with an extra condition of permitting conformal killing vectors (CKV). This work aims to obtain wormhole solutions under these distributions, and through we found that wormhole solutions exist under these Gaussian and Lorentzian sources with viable physical properties. Further, we examine the stability of our obtained solutions through Tolman-Oppenheimer-Volkoff (TOV) equation and found that our calculated results are stable.

gr-qc↗

arXiv2021

A study of anisotropic spheres in $f(Q)$ gravity with quintessence field

This manuscript examines the compact stars in gravity $f (Q)$, where non-metricity $Q$ drives gravitational interactions. To achieve this goal, we consider a spherically symmetric spacetime with the anisotropic fluid distribution. In particular, the quintessence field is used in the energy-momentum tensor to explore the solution of compact stars. In addition, we select three specific types of compact stars, namely HerX-1, SAXJ1808.4-3658, and 4U1820-30. We develop the field equations using the quintessence field of a specific form of $f(Q)$ as $f(Q)=Q-αγ\left(1-\frac{1}{e^{\frac{Q}γ}}\right)$ in $f (Q)$ gravity. In addition, we consider the Schwarzschild metric for the matching conditions at the boundary. Then, we calculate the values of all the relevant parameters by imposing matching conditions. We provide detailed graphical analyses to discuss the parameters' physical viability, namely energy density, pressure, gradient and anisotropy. We also examine the stability of compact stars by testing energy conditions, equations of state, conditions of causality, redshift functions, mass functions, and compactness functions. Finally, we find that the solutions we obtained are physically feasible in modified $f (Q)$ gravity, and also it has good properties for the compact star models.

physics.gen-ph↗

arXiv2021

Constraints on Energy Conditions in $f(R,L_m)$ Gravity

In this manuscript, we consider the extension of the Hilbert-Einstein action to analyze several interesting features of the theory. More specifically, the Lagrangian $f(R)$ is replaced by $f(R, L_m)$ in action, where $R$ is the Ricci scalar, and $L_m$ is the matter Lagrangian. We derive the motion equations for a test particle in the Friedmann-Lemaître-Robertson-Walker (FLRW) flat and homogeneous spacetime. We also derive the energy conditions in this framework. Then, we use the cosmographic parameter such as Hubble, deceleration, jerk, and snap parameters to constraint the model parameters. As a result, we observe that with the constraint range of model parameters our model shows the current accelerated expansion of the universe.

gr-qc↗

arXiv2021

Phantom energy supported wormhole model in $f(R,\,T)$ gravity assuming conformal motion

In this article, we have discussed Morris and Thorne (MT) wormhole solutions in a modified theory of gravity that admits conformal motion. Here we explore the wormhole solutions in $f(R,\,T)$ gravity, which is a function of the Ricci scalar ($R$) and the trace of the stress-energy tensor ($T$). To study wormhole geometries, we make assumption of spherical symmetric static spacetime and the existence of conformal Killing symmetry to get more acceptable astrophysical outcomes. To do this, we choose the expression of $f(R,\,T)$ as $f(R,T)= R+2 γT$. Here we employ the phantom energy EoS relating to radial pressure and density given by $p_r=ωρ$ with $ω<-1$ to constrain our model. Following a discussion of wormhole geometry and behavior of shape function, the study moves on to the computation of proper radial distance, active mass function, the nature of total gravitational energy and a discussion on the violation of energy conditions. We have shown that the wormhole solutions exist for positive as well as negative values of the coupling constant $γ$. From our analysis we see that no wormhole solution exists for $γ=-4π,\,-π(3+ω)$. All the physical parameters have been drawn by employing the values of $γ$ as $γ=-0.3,\,-0.2,\,-0.1,\,0,\,0.1$ and $0.2$, where $γ=0$ corresponds to general relativity (GR) case. It is found that for our proposed model, a realistic wormhole solutions satisfying all the properties can be obtained.

gr-qc↗

arXiv2021

Constraint on the equation of state parameter ($ω$) in non-minimally coupled $f(Q)$ gravity

We study observational constraints on the modified symmetric teleparallel gravity, the non-metricity $f(Q)$ gravity, which reproduces background expansion of the universe. For this purpose, we use Hubble measurements, Baryonic Acoustic Oscillations (BAO), 1048 Pantheon supernovae type Ia data sample which integrate SuperNova Legacy Survey (SNLS), Sloan Digital Sky Survey (SDSS), Hubble Space Telescope (HST) survey, Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1). We confront our cosmological model against observational samples to set constraints on the parameters using Markov Chain Monte Carlo (MCMC) methods. We find the equation of state parameter $ω=-0.853^{+0.015}_{-0.020}$ and $ω= -0.796^{+0.049}_{-0.074}$ for Hubble and Pantheon samples, respectively. As a result, the $f(Q)$ model shows the quintessence behavior and deviates from $Λ$CDM.

gr-qc↗

arXiv2021

Viscous cosmology in the Weyl-type $f(Q,T)$ gravity

Bulk viscosity is the only viscous influence that can change the background dynamics in a homogeneous and isotropic universe. In the present work, we analyze the bulk viscous cosmological model with the bulk viscosity coefficient of the form $ξ=ξ_0+ξ_1H+ξ_2\left(\frac{\dot{H}}{H}+H\right)$ where, $ξ_0$, $ξ_1$ and $ξ_2$ are bulk viscous parameters, and $H$ is the Hubble parameter. We investigate the impact of the bulk viscous parameter on dynamics of the universe in the recently proposed Weyl type $f(Q, T)$ gravity, where $Q$ is the non-metricity, and $T$ is the trace of the matter energy-momentum tensor. The exact solutions to the corresponding field equations are obtained with the viscous fluid and the linear gravity model of the form $f(Q, T)=αQ+\fracβ{6κ^2}T$, where $α$ and $β$ are model parameters. Further, we constrain the model parameters using the $57$ points Hubble dataset and recently released 1048 points Pantheon sample, which shows our model is good congeniality with observations. We study the possible scenarios and the evolution of the universe through the deceleration parameter, the statefinder diagnostics, the Om diagnostics. It is observed that the universe exhibits a transition from a decelerated to an accelerated phase of the universe under certain constraints of model parameters.

gr-qc↗