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P. K. Sahoo

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

At least 73 records · Page 4Linked to original sources
arXiv2023

Cosmological observational constraints on the power law $f(Q)$ type modified gravity theory

In modern cosmology, the curiosity of ultimately understanding the nature of the dark energy controlling the recent acceleration of the Universe motivates us to explore its properties by using some novel approaches. In this work, to explore the properties of dark energy we adopt the modified $f(Q)$ gravity theory, where the non-metricity scalar $Q$, emerging from Weyl geometry, plays the dynamical role. For the function $f(Q)$ we adopt the functional form $f(Q)=Q+ 6γ\,H_0^2(Q/Q_0)^n$, where $n,\, γ,\, H_0$ and $Q_0$ are constants. Then, we test our constructed model against the various observational datasets, such as the Hubble, and the Pantheon+SHOES samples, and their combined sample, through the Markov Chain Monte Carlo (MCMC) statistical analysis. We also employ the parameter estimation technique to constrain the free parameters of the model. In addition, we use the constrained values of the model parameters to explore a few implications of the cosmological model. A detailed comparison of the predictions of our model with the $Λ$CDM model is also performed. In particular, we discuss in detail some cosmographic parameters, like the deceleration, the jerk, and the snap parameters, as well as the behavior of the dark energy and matter energy densities to see the evolution of various energy/matter profiles. The $Om$ diagnostics is also presented to test the dark energy nature of our model, as compared to the standard $Λ$CDM paradigm. Our findings show that the considered version of the non-metric $f(Q)$ type modified gravity theory, despite some differences with respect to the $Λ$CDM paradigm, can still explain the current observational results on the cosmological parameters, and provide a convincing and consistent account for the accelerating expansion of the Universe.

gr-qc↗
arXiv2023

Big Bang Nucleosynthesis constraints on $f(T, \mathcal{T})$ gravity

Big Bang Nucleosynthesis provides us with an observational insight into the very early Universe. Since this mechanism of light element synthesis comes out of the standard model of particle cosmology which follows directly from General Relativity, it is expected that any modifications to GR will result in deviations in the predicted observable parameters which are mainly, the neutron-to-proton ratio and the baryon-to-photon ratio. We use the measured neutron-to-proton ratio and compare the theoretically obtained expressions to constrain two models in the framework of $ f(T,\mathcal{T}) $ gravity. The theoretically constrained models are then tested against observational data from the Hubble dataset and the $ Λ$CDM model to explain the accelerated expansion of the Universe.

astro-ph.CO↗
arXiv2023

Cosmological reconstruction and $Λ$CDM universe in $f(Q,C)$ gravity

Symmetric Teleparallel Gravity allows for the reformulation of gravity in the form of nonmetricity by vanishing the contorsion term in the generic affine connection. Our focus is on investigating a recently proposed extension of this theory in which the Lagrangian has the form $f(Q,C)$ by incorporating the boundary term $C$. In this work, we first use a reconstruction approach in $f(Q,C)$ gravity that might admit the $Λ$CDM expansion history. Furthermore, we perform a novel approach for cosmological reconstruction of $f(Q,C)$ gravity in terms of e-folding, and it shows how any FLRW cosmology can arise from a specific $f(Q,C)$ gravity. A variety of instances are provided using this approach in which $f(Q, C)$ gravity is reconstructed to yield the well-known cosmic evolution: $Λ$CDM era, acceleration/deceleration era which is equivalent to the presence of phantom and non-phantom matter, late-time acceleration with the crossing of phantom-divide line and transient phantom era.

gr-qc↗
arXiv2023

AdS black hole thermodynamics and microstructures from $f(Q)$ gravitation

The significant properties and phase transition of charged Anti-de Sitter (AdS) black holes have been extensively studied in a variety of modified theories of gravity in the presence of numerous matter fields. The goal of our current research is to investigate the AdS black hole's thermodynamics under the impact of $f(Q)$ gravity. Additionally, this paper explores the black hole's local stability and phase structure under the relevant gravity. Besides, we use Ruppeiner geometry to look into the AdS black hole's microscopic structure. We have numerically computed the Ricci curvature scalar $R$ to explain the interactions between the AdS black hole's microscopic particles under the influence of $f(Q)$ gravity.

gr-qc↗
arXiv2023

Cosmology in $f(R,L_m)$ gravity

In this letter, we investigate the cosmic expansion scenario of the universe in the framework of $f(R,L_m)$ gravity theory. We consider a non-linear $f(R,L_m)$ model, specifically, $f(R,L_m)=\frac{R}{2}+L_m^n + β$, where $n$ and $β$ are free model parameters. Then we derive the motion equations for flat FLRW universe and obtain the exact solution of corresponding field equations. Then we estimate the best fit ranges of model parameters by using updated $H(z)$ datasets consisting of 57 points and the Pantheon datasets consisting of 1048 points. Further we investigate the physical behavior of density and the deceleration parameter. The evolution of deceleration parameter depicts a transition from deceleration to acceleration phases of the universe. Moreover, we analyze the stability of the solution of our cosmological model under the observational constraint by considering a linear perturbation. Lastlty, we investigate the behavior of Om diagnostic parameter and we observe that our model shows quintessence type behavior. We conclude that our $f(R,L_m)$ cosmological model agrees with the recent observational studies and can efficiently describe the late time cosmic acceleration.

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arXiv2023

Slow-roll inflation in $f(T,\mathcal{T})$ modified gravity

In this article, we explore the concept of cosmological inflation within the framework of the $f (T,\mathcal{T})$ theory of gravity, where $f$ is a general function of the Torsion scalar $T$ and the trace, $\mathcal{T}$, of the energy-momentum tensor. It is assumed that the conditions of slow-roll inflation are applicable in$f (T,\mathcal{T})$ gravity. To determine different observables related to inflation, such as the tensor-to-scalar ratio $r$, scalar spectral index $n_s$, spectral index $ α_s $, and tensor spectral index $n_t$, the Hubble slow-roll parameters are utilized for a particular model of $f (T,\mathcal{T})$. Lastly, an assessment has been carried out to determine the feasibility of the models by conducting a numerical analysis of the parameters. The findings indicate that it is feasible to achieve compatibility with the observational measurements of slow-roll parameters by utilizing different values of the free parameters.

gr-qc↗
arXiv2023

Dynamical system analysis of scalar field cosmology in coincident $f(Q)$ gravity

In this article, we investigate scalar field cosmology in the coincident $f(Q)$ gravity formalism. We calculate the motion equations of $f(Q)$ gravity under the flat Friedmann-Lemaître-Robertson-Walker background in the presence of a scalar field. We consider a non-linear $f(Q)$ model, particularly $f(Q)=-Q+αQ^n$, which is nothing but a polynomial correction to the STEGR case. Further, we assumed two well-known specific forms of the potential function, specifically the exponential from $V(ϕ)= V_0 e^{-βϕ}$ and the power-law form $V(ϕ)= V_0ϕ^{-k}$. We employ some phase-space variables and transform the cosmological field equations into an autonomous system. We calculate the critical points of the corresponding autonomous systems and examine their stability behaviors. We discuss the physical significance corresponding to the exponential case for parameter values $n=2$ and $n=-1$ with $β=1$, and $n=-1$ with $β=\sqrt{3}$. Moreover, we discuss the same corresponding to the power-law case for the parameter value $n=-2$ and $k=0.16$. We also analyze the behavior of corresponding cosmological parameters such as scalar field and dark energy density, deceleration, and the effective equation of state parameter. Corresponding to the exponential case, we find that the results obtained for the parameter constraints in Case III is better among all three cases, and that represents the evolution of the universe from a decelerated stiff era to an accelerated de-Sitter era via matter-dominated epoch. Further, in the power-law case, we find that all trajectories exhibit identical behavior, representing the evolution of the universe from a decelerated stiff era to an accelerated de-Sitter era. Lastly, we conclude that the exponential case shows better evolution as compared to the power-law case.

gr-qc↗
arXiv2023

Wormhole Geometry and Three-Dimensional Embedding in Extended Symmetric Teleparallel Gravity

In the present manuscript, we study traversable wormhole solutions in the background of extended symmetric teleparallel gravity with matter coupling. With the anisotropic matter distribution we probe the wormhole geometry for two different gravity models. Primarily, we consider the linear model $ f(Q,T) =Q + 2 \, ξ\,T$. Firstly, we presume a logarithmic form of shape function and analyze the scenario for different redshift functions. Secondly, for a specific form of energy density, we derive a shape function and note its satisfying behavior. Next, for the non-linear model $f(Q,T) = Q + α,Q^2 + β,T$ and a specific shape function we examine the wormhole solution. Further, with the aid of embedding diagrams, we interpreted the geometry of wormhole models. Finally, we conclude results.

gr-qc↗
arXiv2023

Physical Characteristics and Maximum Allowable Mass of Hybrid Star in the Context of $f(Q)$ Gravity

In this study, we explore several new characteristics of a static anisotropic hybrid star with strange quark matter (SQM) and ordinary baryonic matter (OBM) distribution. Here, we use the MIT bag model equation of state to connect the density and pressure of SQM inside stars, whereas the linear equation of state $p_r =αρ-β$ connects the radial pressure and matter density caused by baryonic matter. The stellar model was developed under a background of $f(Q)$ gravity using the quadratic form of $f(Q)$. We utilized the Tolman-Kuchowicz ansatz to find the solutions to the field equations under modified gravity. We have matched the interior solution to the external Schwarzschild spacetime in order to acquire the numerical values of the model parameters. We have selected the star Her X-1 to develop various profiles of the model parameters. Several significant physical characteristics have been examined analytically and graphically, including matter densities, tangential and radial pressures, energy conditions, anisotropy factor, redshirt, compactness, etc. The main finding is that there is no core singularity present in the formations of the star under investigation. The nature of mass and the bag constant $B_g$ have been studied in details through equi-mass and equi-$B_g$ contour. The maximum allowable mass and the corresponding radius have been obtained via $M-R$ plots.

gr-qc↗
arXiv2023

GUP Corrected Casimir Wormholes in $f(Q)$ Gravity

We have presented systematically the effect of the Generalized Uncertainty Principle (GUP) in Casimir wormholes space-time in the recently proposed modified gravity, the so-called symmetric teleparallel gravity or $f(Q)$ gravity. Here $Q$ is the non-metricity scalar that drives the gravitation interaction. We consider two famous GUP relations, such as the Kempf, Mangano, and Mann (KMM) model and the Detournay, Gabriel, and Spindel (DGS) model, in our study. Besides this, we investigate with three different redshift functions under anisotropic fluid located at the throat. Further, we analyzed the obtained wormhole solutions with energy conditions, especially null energy conditions (NEC) at the throat of the wormhole, and encountered that some arbitrary quantity disrespects the classical energy conditions at the wormhole throat of radius $r_0$. Later, the ADM mass and the volume integral quantifier are also discussed to calculate the amount of exotic matter required near the wormhole throat. Additionally, we show the behavior of the equation of state parameters under the effect of GUP.

gr-qc↗
arXiv2023

Existence of Wormhole Solutions in $f(Q,T)$ Gravity under Non-commutative Geometries

In this paper, we have systematically discussed the existence of the spherically symmetric wormhole solutions in the framework of $f(Q,\,T)$ gravity under two interesting non-commutative geometries such as Gaussian and Lorentzian distributions of the string theory. Also, to find the solutions, we consider two $f(Q,\,T)$ models such as linear $f(Q,\,T)=α\,Q+β\,T$ and non-linear $f(Q,\,T)=Q+λ\,Q^2+η\,T$ models in our study. We obtained analytic and numerical solutions for the above models in the presence of both non-commutative distributions. We discussed wormhole solutions analytically for the first model and numerically for the second model and graphically showed their behaviors with the appropriate choice of free parameters. We noticed that the obtained shape function is compatible with the flare-out conditions under asymptotic background. Further, we checked energy conditions at the wormhole throat with throat radius $r_0$ and found that NEC is violated for both models under non-commutative background. At last, we examine the gravitational lensing phenomenon for the precise wormhole model and determine that the deflection angle diverges at the wormhole throat.

gr-qc↗
arXiv2023

On possible wormhole solutions supported by non-commutative geometry within $f(R, L_m)$ gravity

Non-commutativity is a key feature of spacetime geometry. The current article explores the traversable wormhole solutions in the framework of $f(R,L_m)$ gravity within non-commutative geometry. By using the Gaussian and Lorentzian distributions, we construct tideless wormholes for the nonlinear $f(R,L_m)$ model $f(R,L_m)=\dfrac{R}{2}+L_m^α$. For both cases, we derive shape functions and discuss the required different properties with satisfying behavior. For the required wormhole properties, we develop some new constraints. The influence of the involved model parameter on energy conditions is analyzed graphically which provides a discussion about the nature of exotic matter. Further, we check the physical behavior regarding the stability of wormhole solutions through the TOV equation. An interesting feature regarding the stability of the obtained solutions via the speed of sound parameters within the scope of average pressure is discussed. Finally, we conclude our results.

gr-qc↗
arXiv2023

Thin-Shell Gravastar Model in $f(Q,T)$ Gravity

In the last few decades, gravastars have been proposed as an alternative to black holes. The stability of the gravastar has been studied in many modified theories of gravity along with Einstein's GR. The $f(Q,T)$ gravity, a successfully modified theory of gravity for describing the current accelerated expansion of the Universe, has been used in this article to study gravastar in different aspects. According to Mazur and Mottola (Proc. Natl. Acad. Sci 101, 9545 (2004)), it has three regions with three different equations of state. Here in this work, we have studied the interior of the gravastar by considering the $p=-ρ$ EoS to describe the dark sector for the interior region. The next region is a thin shell of ultrarelativistic stiff fluid, in which we have investigated several physical properties, viz., the proper length, energy, entropy, surface energy density, etc. In addition, we have studied the surface redshift and speed of sound to check the potential stability of our proposed thin-shell gravastar model. Apart from that, we have used the entropy maximization technique to verify the stability of the gravastar model. The gravastar's outer region is a complete vacuum described by exterior Schwarzschild geometry. Finally, we have presented a stable gravastar model which is singularity-free and devoid of any incompleteness in classical black hole theory.

gr-qc↗
arXiv2023

Correction to Lagrangian for Bouncing Cosmologies in $f(Q)$ Gravity

Symmetric teleparallel gravity offers to reformulate the gravitational formalism without the presence of curvature and torsion with the help of non-metricity tensors. Interestingly, Symmetric teleparallel gravity can be formulated equivalently to teleparallel gravity or general relativity for an appropriate setup. In this study, our aim lies in exploring the bouncing cosmologies as an alternative to the initial singularity of the Universe in the background of modified symmetric teleparallel gravity. To explore this, we adopt the reconstruction technique to present the possible reconstructed Lagrangian for various cosmological bouncing solutions in a flat Friedmann-Lemaître-Robertson-Walker spacetime with a perfect fluid matter distribution. We study the reconstructed gravitational Lagrangians, which are capable of reproducing analytical solutions for \textit{symmetric bounce}, \textit{super-bounce}, \textit{oscillatory bounce}, \textit{matter bounce}, and \textit{exponential bouncing} model settings. Further, we examine the dark energy profiles of the models using reconstructed Lagrangians. In addition, we found that an additional term arises in each reconstructed Lagrangian compared to general relativity (GR). That extra term corrected the background GR to present bouncing cosmology in modified gravity. These newly motivated cosmological models may have an effect on gravitational phenomena at other cosmological scales.

gr-qc↗
arXiv2023

Wormhole solutions in $f(R,L_m)$ gravity

In this work, we intend to explore wormhole geometries in the framework of $f(R,L_m)$ gravity. We derive the field equations for the generic $f(R,L_m)$ function by assuming the static and spherically symmetric Morris-Thorne wormhole metric. Then we consider two non-linear $f(R,L_m)$ model, specifically, $f(R,L_m)=\frac{R}{2}+L_m^α$ and $f(R,L_m)=\frac{R}{2}+(1+λR)L_m$, where $α$ and $λ$ are free model parameters. We obtain the wormhole solutions by assuming three cases, namely, a linear barotropic EoS, anisotropic EoS, and isotropic EoS corresponding to model I. We observe that for both barotropic and anisotropic cases, the corresponding wormhole solutions obey the flaring-out condition under asymptotic background, while for the isotropic case, the shape function does not follow the flatness condition. Also, we find that the null energy condition exhibits negative behavior in the vicinity of the throat. Further, we consider two different shape functions to investigate the behavior of model II. We find some constraints on the model parameter for which the violation of the null energy condition exhibits. Finally, we employ the volume integral quantifier to calculate the amount of exotic matter required near the wormhole throat for both models. We conclude that the modification of standard GR can efficiently minimize the use of exotic matter and provide stable traversable wormhole solutions.

gr-qc↗
arXiv2023

$H_0$ Tension in Torsion-based Modified Gravity

The rising concern in the Hubble constant tension ($H_0$ tension) of the cosmological models motivates the scientific community to search for alternative cosmological scenarios that could resolve the $H_0$ tension. In this regard, we aim to work on a torsion-based modified theory of gravity which is an alternative description to the coherence model. We solve numerically for the Hubble parameter using two exponential Lagrangian functions of torsion $T$ and a trace of energy-momentum tensor $\mathcal{T}$ for the dust case. Further, we constrain the cosmological and model parameters; to do that, we use Hubble, SNe Ia, Baryon Acoustic Oscillations, Cosmic Microwave Background samples, and Markov Chain Monte Carlo (MCMC) simulation through Bayesian statistics. We obtain the values of Hubble constant $H_0$ for our model, and the outputs align with the recent observational measurements of $H_0$. In addition, we check the deviation of our results from model-independent measurements of $H_0$ from Planck2018, S$H_0$ES, and $H_0$LiCOW experiments. In contrast, our finding partially solved the $H_0$ tension but gave a new possible direction to alleviate the $H_0$ tension.

astro-ph.CO↗
arXiv2023

Scalar field evolution at background and perturbation levels for a broad class of potentials

In this paper, we investigate a non-interacting scalar field cosmology with an arbitrary potential using the $f$-deviser method that relies on the differentiability properties of the potential. Using this alternative mathematical approach, we present a unified dynamical system analysis at a scalar field's background and perturbation levels with arbitrary potentials. For illustration, we consider a monomial and double exponential potential. These two classes of potentials comprise the asymptotic behaviour of several classes of scalar field potentials, and, therefore, they provide the skeleton for the typical behaviour of arbitrary potentials. Moreover, we analyse the linear cosmological perturbations in the matterless case by considering three scalar perturbations: the evolution of the Bardeen potentials, the comoving curvature perturbation, the so-called Sasaki-Mukhanov variable, or the scalar field perturbation in uniform curvature gauge. Finally, an exhaustive dynamical system analysis for each scalar perturbation is presented, including the evolution of Bardeen potentials in the presence of matter.

gr-qc↗
arXiv2023

Constraining $f(T,\mathcal{T})$ Gravity with Gravitational Baryogenesis

Gravitational baryogenesis is one of the mechanisms which help us to explore more about our early universe, especially baryon-anti-baryon asymmetry. As we know, modified theories of gravity are very successful in describing the present accelerated scenario of the universe. Therefore, in this letter, we aim to constrain the generalized torsion-based modified theory of gravity, namely, $f(T,\mathcal{T})$ gravity with gravitational baryogenesis, where $T$, $\mathcal{T}$ are the torsion scalar, trace of the energy-momentum tensor, respectively. For this, we examine how the various Lagrangian forms of $f(T,\mathcal{T})$ affect the baryogenesis. We also impose the constraints on the extra degrees of freedom induced by modified theory with the observational values of the baryon-to-entropy ratio. In addition, we further explore how more generalized gravitational baryogenesis can attribute in a physically viable and consistent way to the cosmologies of the modified theory of gravity.

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