arXiv subjects

P. K. Sahoo

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

At least 55 records · Page 3Linked to original sources

arXiv2024

Cosmological constraints in symmetric teleparallel gravity with bulk viscosity

In this study, we explore the accelerated expansion of the universe within the framework of modified $f(Q)$ gravity. The investigation focus on the role of bulk viscosity in understanding the universe's accelerated expansion. Specifically, a bulk viscous matter-dominated cosmological model is considered, with the bulk viscosity coefficient expressed as $ζ= ζ_0 ρH^{-1} + ζ_1 H $. We consider the power law $f(Q)$ function $f(Q)=αQ^n $, where $α$ and $n$ are arbitrary constants and derive the analytical solutions for the field equations corresponding to a flat FLRW metric. Subsequently, we used the combined Cosmic Chronometers (CC)+Pantheon+SH0ES sample to estimate the free parameters of the obtained analytic solution. We conduct Bayesian statistical analysis to estimate the posterior probability by employing the likelihood function and the MCMC random sampling technique, along with the AIC and BIC statistical assessment criteria. In addition, we explore the evolutionary behavior of significant cosmological parameters. The effective equation of state (EOS) parameter predicts the accelerating behavior of the cosmic expansion phase. Further, by the statefinder and $Om(z)$ diagnostic test, we found that our viscous model favors quintessence-type behavior and can successfully describe the late-time scenario.

gr-qc↗

arXiv2024

Possibility of the Traversable Wormholes in the Galactic Halos within $4D$ Einstein-Gauss-Bonnet Gravity

Recently, there has been significant interest regarding the regularization of a $D\rightarrow 4$ limit of Einstein-Gauss-Bonnet (EGB) gravity. This regularization involves re-scaling the Gauss-Bonnet (GB) coupling constant as $α/(D-4)$, which bypasses Lovelock's theorem and avoids Ostrogradsky instability. A noteworthy observation is that the maximally or spherically symmetric solutions for all the regularized gravities coincide in the $4D$ scenario. Considering this, we investigate the wormhole solutions in the galactic halos based on three different choices of dark matter (DM) profiles, such as Universal Rotation Curve, Navarro-Frenk-White, and Scalar Field Dark Matter with the framework of $4D$ EGB gravity. Also, the Karmarkar condition was used to find the exact solutions for the shape functions under different non-constant redshift functions. We discussed the energy conditions for each DM profile and noticed the influence of GB coefficient $α$ in violating energy conditions, especially null energy conditions. Further, some physical features of wormholes, viz. complexity factor, active gravitational mass, total gravitational energy, and embedding diagrams, have been explored.

gr-qc↗

arXiv2024

Gravastar model in Krori-Barua metric under $f(Q)$ gravity

In this paper, we explore the characteristics of a gravastar in $f(\mathcal{Q})$ gravity, which is upheld by Krori-Barua (KB) metric. We have used Krori-Barua (KB) metric for the interior and shell regions of the gravastar. We deduced our field equations by using Krori-Barua metric. In the outside regions of the gravastar, we have taken two regular black hole metrics. Additionally, we have applied the Israel junction condition to calculate the potential difference across the thin shell concerning different types of regular black holes, such as Bardeen and Hayward. We have also discussed the physical properties like proper length, entropy, energy, EoS and stability.

gr-qc↗

arXiv2024

Exploring wormhole solutions with global monopole charge in the context of $f(Q)$ gravity

This study explores the potential existence of traversable wormholes influenced by a global monopole charge within the $f(Q)$ gravity framework. To elucidate the characteristics of these wormholes, we conducted a comprehensive analysis of wormhole solutions employing three different forms of redshift function under a linear $f(Q)$ model. Wormhole shape functions were derived for barotropic, anisotropic, and isotropic Equations of State (EoS) cases. However, in the isotropic EoS case, the calculated shape function failed to satisfy the asymptotic flatness condition. Additionally, we observed that our obtained shape functions adhered to the flaring-out conditions under an asymptotic background for the remaining EoS cases. Furthermore, we examined the energy conditions at the wormhole throat with a radius $r_0$. We noted the influences of the global monopole's parameter $η$, the EoS parameter $ω$, and $n$ in violating energy conditions, particularly the null energy conditions. Finally, we conducted a stability analysis utilizing the Tolman-Oppenheimer-Volkov (TOV) equation and found that our obtained wormhole solution is stable.

gr-qc↗

arXiv2024

Constraining extended teleparallel gravity via cosmography: A model-independent approach

As a classical approach, the dynamics of the Universe, influenced by its dark components, are unveiled through prior modifications of Einstein's equations. Cosmography, on the other hand, is a highly efficient tool for reconstructing any modified theory in a model-independent manner. By employing kinematic variables, it offers a profound explanation for cosmic expansion. Although the cosmographical approach has been highly successful in several geometric theories in recent years, it has not been extensively explored in coupled gravities. With this in mind, we intend to constrain an extended teleparallel gravity model, $f(T,\mathcal{T})$, through cosmographic parameters. We utilize Taylor series expansion, assuming a minimally coupled form, to constrain the unknowns involved in the series. To achieve this, we conduct a Markov Chain Monte Carlo analysis (MCMC) using three different datasets (CC, BAO, and Pantheon+SH0ES). The constrained results obtained from MCMC are then compared and verified using various cosmological parameters. Finally, we compare the resulting models with \textbf{three} well-known $f(T,\mathcal{T})$ models.

gr-qc↗

arXiv2024

Energy conditions in the $f(R,L,T)$ theory of gravity

We construct the energy conditions for the recently proposed $f(R,L,T)$ gravity theory, for which $f$ is a generic function of the Ricci scalar $R$, matter lagrangian density $L$ and trace of the energy-momentum tensor $T$. We analyse two different forms for the $f(R,L,T)$ function within the framework of the Friedmann-Lemâitre-Robertson-Walker universe. We constrain the model parameters from the energy conditions. This approach allows us to assess the feasibility of specific forms of the $f(R,L,T)$ gravity.

gr-qc↗

arXiv2024

Extended Bose-Einstein condensate dark matter in $f(Q)$ gravity

In this article, we attempt to explore the dark sector of the universe i.e. dark matter and dark energy, where the dark energy components are related to the modified $f(Q)$ Lagrangian, particularly a power law function $f(Q)= γ\left(\frac{Q}{Q_0}\right)^n$, while the dark matter component is described by the Extended Bose-Einstein Condensate (EBEC) equation of state for dark matter, specifically, $p = αρ+ βρ^2$. We find the corresponding Friedmann-like equations and the continuity equation for both dark components along with an interacting term, specifically $\mathcal{Q} = 3b^2H ρ$, which signifies the energy exchange between the dark sector of the universe. Further, we derive the analytical expression of the Hubble function, and then we find the best-fit values of free parameters utilizing the Bayesian analysis to estimate the posterior probability and the Markov Chain Monte Carlo (MCMC) sampling technique corresponding to CC+Pantheon+SH0ES samples. In addition, to examine the robustness of our MCMC analysis, we perform a statistical assessment using the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). Further from the evolutionary profile of the deceleration parameter and the energy density, we obtain a transition from the decelerated epoch to the accelerated expansion phase, with the present deceleration parameter value as $q(z=0)=q_0=-0.56^{+0.04}_{-0.03}$ ($68 \%$ confidence limit), that is quite consistent with cosmological observations. In addition, we find the expected positive behavior of the effective energy density. Finally, by examining the sound speed parameter, we find that the assumed theoretical $f(Q)$ model is thermodynamically stable.

gr-qc↗

arXiv2024

Bouncing cosmological models in $f(R,L_m)$ gravity

This article explores matter bounce non-singular cosmology in $f(R,L_m)$ gravity. We consider two non-linear $f(R,L_m)$ functional forms, specifically, $f(R,L_m) = \frac{R}{2} + λR^2 + αL_m$ and $f(R,L_m) = \frac{R}{2} + L_m ^β+ γ$ representing a minimal coupling case. We derive the corresponding Friedmann-like equations for both the assumed models in the FLRW background, and then we present the impact of the model parameters along with the parameter of bouncing scale factor on the equation of state parameter, pressure, and the energy density. In addition, we examine the dynamical behavior of cosmographic parameters such as jerk, lerk, and snap parameters. Further, we find that the violation of the null energy condition along with the strong energy condition depicts the non-singular accelerating behavior, corresponding to both assumed non-linear $f(R,L_m)$ functions. Lastly, we present the behavior of the adiabatic speed of sound to examine the viability of the considered cosmological bouncing scenario.

gr-qc↗

arXiv2024

Modified $f(Q)$ gravity models and their cosmological consequences

In this work, we consider three different $f(Q)$ models, such as power-law, exponential, and logarithmic, to study which model better mimics $Λ$CDM evolution theoretically. Henceforth, we determine solutions to the $f(Q)$ gravity field equations in the isotropic and homogeneous universe. Since all the models contain two model parameters, we reduce the degrees of freedom using the first Friedman equation at the present time. Further, we check the behavior of cosmological parameters using the obtained solution to the field equations and compare it with the $Λ$CDM model. As a result, the power-law model shows a good match with $Λ$CDM model for $λ=-1$ and $λ=-2$, while the exponential model behaves well for the range $5\le β<11$, and the logarithmic model matches for $3.8<γ<4.4$.

gr-qc↗

arXiv2024

Revisiting kink-like parametrization and constraints using OHD/Pantheon+/BAO samples

We reexamine the kink-like parameterization of the deceleration parameter to derive constraints on the transition redshift from cosmic deceleration to acceleration. This is achieved using observational Hubble data, Type Ia Supernovae Pantheon+ samples and Baryon acoustic oscillations. In this parametrization, the value of the initial $q$ parameter is $q_{i}$, the final value is $q_f$, the present value is denoted by $q_{0}$, and the transition duration is given by $α$. We perform our calculations using the Monte Carlo Markov Chain method, utilizing the emcee package. Under the assumption of a flat geometry, we constrain the range of possible values for three scenarios: when $q_{f}$ is unrestricted, when $q_{f}$ is equal to $-1$, and when $α$ is $1/3$. This is done assuming that $q_{i}=1/2$. Here, we achieve that the $SN$ data fixes the free parameters tightly as in the flat $Λ$CDM for unrestricted $q_{f}$. In addition, if we fix $q_{f}=-1$, the model behaves well as the $Λ$CDM for the combined dataset. We also acquire the current value of the deceleration parameter, which is consistent with the latest results that assume the $Λ$CDM model. Furthermore, we observe a deviation from the standard $Λ$CDM model in the current model based on the evolution of $j(z)$, and it is evident that the universe transitions from deceleration to acceleration and will eventually reach the $Λ$CDM model in the near future.

astro-ph.CO↗

arXiv2024

Probing Baryogenesis in $f(Q)$ gravity

The origin of matter domination in the Universe is one of the most exciting open puzzles in particle physics and cosmology. Despite many theoretical developments, the actual reason behind baryon-antibaryon asymmetry is still unknown. Our aim here is to examine this phenomenon in the framework of modified gravity theories, which have impressively elucidated the contemporary accelerated expansion of the universe as well as the early phase. Consequently, this letter sets its sights on the task of constraining a specific variant of modified gravity, namely, $f(Q)$ gravity, in conjunction with gravitational baryogenesis. The Power Law model and recently proposed DGP-like $f(Q)$ models are considered to find the baryon-to-entropy ratio and compare them with the observed value, that is ${n_B}/s=9.42\times 10^{-11}$. Furthermore, we impose constraints on the additional degrees of freedom introduced by this modified theory of gravity.

gr-qc↗

arXiv2024

Wormhole solutions under the effect of dark matter in $f(R,L_m)$ gravity

In the background of $f(R, L_m)$ gravity, this work investigates three distinct dark matter halo profiles to test the possibility of generalised wormhole geometry within the galactic halo regions. The current study aims to accomplish these goals by examining various dark matter profiles including Universal Rotation Curves (URC), Navarro-Frenk-White (NFW) model-I, and NFW model-II inside two distinct $f(R, L_m)$ gravity models. According to the $f(R, L_m) = \frac{R}{2} + L_m^α$ model, the DM halo density profiles produce suitable shape functions that meet all the necessary requirements for exhibiting the wormhole geometries with appropriate choice of free parameters. In addition, to examine DM profiles under the $f(R, L_m) = \frac{R}{2} + (1 + λR)L_m$ model, we consider a specific shape function. Further, we observed that the derived solution from both two models violates the null energy constraints, confirming that the DM supports wormholes to maintain in the galactic halo.

gr-qc↗

arXiv2024

A Comprehensive Study of Massive Compact Star Admitting Conformal Motion Under Bardeen Geometry

This article primarily investigates the existence of the charged compact star under the conformal motion treatment within the context of f(Q) gravity. We have developed two models by implementing the power-law and linear form of conformal factor, enabling an in-depth comparison in our study. We have selected the MIT Bag model equation of state to describe the connection between pressure and energy density and matched the interior spherically symmetric space-time with the Bardeen space-time. In addition, the present research examines various physically valid characteristics of realistic stars, such as PSR J1614-2230, PSR J1903+327, Vela X-1, Cen X-3, and SMC X-1. We compare two constructed models by attributing the behavior of density, pressure, equilibrium conditions, and the adiabatic index. We have additionally included a brief analysis of the scenario involving Reissner-Nordstrom spacetime as an external geometry for the matching condition. In contrast to the Reissner-Nordstrom instance, the Bardeen model with the extra term in the asymptotic representations yields a more intriguing and viable result. The current analysis reveals that the resulting compact star solutions are physically acceptable and authentic when considering the presence of charge with conformal motion in f(Q) gravity.

gr-qc↗

arXiv2024

Study of charged gravastar model in $f(\mathcal{Q})$ gravity

In recent days gravastar has been a very lucrative alternative to black holes, as it does not suffer from the singularity problem as well and it is based on sound physical grounds. Modified Symmetric teleparallel equivalent of gravity also has seen quite a few successes in recent years both in cosmology as well as in astrophysical objects like black holes and wormholes. In this paper, we have considered the charged gravastar in $f(\mathcal{Q})$ formulation and have solved it fully analytically and found various physical characteristics like energy density, entropy and EoS for the gravastar. We have used the Israel junction condition to make some phenomenological predictions regarding the potential of the thin shell around the gravastar. We have also studied the deflection of the angle caused by the gravastar. Finally, we conclude by noting how future radio telescopes could detect the gravastar shadow and how can one distinguish it from the black hole event horizon.

gr-qc↗

arXiv2024

Impact of dark matter galactic halo models on wormhole geometry within $f(Q,T)$ gravity

This study investigates the possible existence of wormhole solutions with dark matter galactic halo profiles in the background of $f(Q,T)$ gravity. The primary focus of the current study is to find the significance of dark matter (DM) in the search for traversable wormhole solutions within galactic halos. Various dark matter profiles, such as Universal Rotation Curves (URC), Navarro-Frenk-White (NFW) model-I, and NFW model-II, are examined within two different $f(Q,T)$ models. The DM halo density profiles generate appropriate shape functions under the linear model that satisfy all the essential conditions for presenting the wormhole geometries. Apart from that, we take into account an embedded wormhole-specific shape function to inspect DM profiles under the non-linear model. We noticed that the null energy conditions are violated by the obtained solution from each model, which confirms that the DM support wormholes to sustain in the galactic halo. The findings reveal that the solutions obtained for different density profiles of dark matter halos within generalized symmetric teleparallel gravity demonstrate viability.

physics.gen-ph↗

arXiv2024

Conformally symmetric wormhole solutions supported by non-commutative geometries in the context of $f(Q,T)$ gravity

This paper examines wormhole geometries in the context of $f(Q,T)$ gravity under the background of non-commutative distributions. We discuss the analytical solutions assuming spherical symmetry and the presence of conformal Killing vectors, which provides a systematic approach for seeking exact wormhole solutions. Specifically, the imposition of conformal symmetry places noteworthy constraints on the model, shaping the analytical outcomes more precisely. We studied the properties of traversable wormholes under both Gaussian and Lorentzian distributions and noticed that NEC and SEC are violated in the neighborhood of the wormhole throat. We also observed the influence of model parameters as well as non-commutative parameters for these violations. Employing the "volume integral quantifier," it is established that conformally symmetric wormhole geometries may, in principle, be constructed with infinitesimally small amounts of matter, violating the averaged null energy condition. Further, equilibrium forces and the complexity factor of the non-commutative distributed wormholes have also been explored.

gr-qc↗

arXiv2024

Phase-space analysis of the viscous fluid cosmological models in the coincident $f(Q)$ gravity

In this article, we consider a newly proposed parameterization of the viscosity coefficient $ζ$, specifically $ζ=\barζ_0 {Ω^s_m} H $, where $\barζ_0 = \frac{ζ_0}{Ω^s_{m_0}} $ within the coincident $f(Q)$ gravity formalism. We consider a non-linear function $f(Q)= -Q +αQ^n$, where $α$ and $n$ are arbitrary model parameters, which is a power-law correction to the STEGR scenario. We find an autonomous system by invoking the dimensionless density parameters as the governing phase-space variables. We discuss the physical significance of the model corresponding to the parameter choices $n=-1$ and $n=2$ along with the exponent choices $s=0, 0.5$, and $1.05$. We find that model I shows the stable de-Sitter type or stable phantom type (depending on the choice of exponent $s$) behavior with no transition epoch, whereas model II shows the evolutionary phase from the radiation epoch to the accelerated de-Sitter epoch via passing through the matter-dominated epoch. Hence, we conclude that model I provides a good description of the late-time cosmology but fails to describe the transition epoch, whereas model II modifies the description in the context of the early universe and provides a good description of the matter and radiation era along with the transition phase.

gr-qc↗

arXiv2024

Exploring wormhole solutions in curvature-matter coupling gravity supported by noncommutative geometry and conformal symmetry

This article explores new physically viable wormhole solutions within the framework of f(R,Lm) gravity theory, incorporating noncommutative backgrounds and conformal symmetries. The study investigates the impact of model parameters on the existence and properties of wormholes. The derived shape function is found to obey all the required criteria. Specific attention is given to traceless wormholes with Gaussian and Lorentzian distributions, investigating the behavior of the shape functions and energy conditions. In both cases, the presence of exotic fluid is confirmed.

gr-qc↗