arXiv subjects

P. K. Sahoo

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

At least 37 records · Page 2Linked to original sources

arXiv2024

Reconstruction of the scalar field potential in nonmetricity gravity through Gaussian processes

The accelerated expansion of the universe has been widely confirmed, posing challenges to the standard $Λ$CDM model, particularly the cosmological coincidence problem. This has motivated the exploration of modified gravity theories, including non-metricity gravity, which explains cosmic acceleration without dark energy. In this work, we incorporate a quintessence scalar field into the non-metricity framework to model both inflation and late-time acceleration. Employing the Gaussian process method with a square exponential kernel, we reconstruct the scalar field potential, $V(ϕ)$, from observational Hubble data sets coming from cosmic chronometers (CC) as well as from the method of radial baryon acoustic oscillations (BAO) in a model-independent approach. This approach allows us to obtain a suitable quintessence scalar field model that aligns with the observational Hubble data under the framework of power-law non-metricity gravity. Additionally, we compare our reconstructed potential with power-law scalar field potentials, revealing that these models show better agreement with the observational data, providing new insights into the dynamics of the universe. In contrast, we find that the early dark energy has minimal effect on the present-time accelerated expansion of the universe.

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arXiv2024

Chebyshev cosmography in the framework of extended symmetric teleparallel theory

Cosmography has been extensively utilized to constrain the kinematic state of the Universe using measured distances. In this work, we propose a new method to reconstruct coupling theories using the first kind of Chebyshev polynomial for two variables in which the functional form of the $f(Q,T)$ theory has been obtained. Further, the unknowns that appeared in the series are constrained using the cosmographic parameters. We find the explicit form of the luminosity distance in terms of cosmographic parameters to perform MCMC analysis using the PANTHEON+SH0ES data set. Through the distance modulus function, we observe that the result comes out to be an excellent match to the standard cosmological model and data.

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arXiv2024

GUP corrected Casimir Wormholes with Electric Charge in $f(R,L_m)$ Gravity

In this letter, we study and investigate the effects of the Generalised Uncertainty Principle (GUP) and electric charge on Casimir wormhole geometry in the Curvature-Lagrangian coupled $f(R,L_m)$ gravity. The functional form of the considered model is $f(R,L_m)=\frac{R}{2κ}+L_m^{\,\,α}$, corresponding to it the analytic shape function is found. For our analysis, we study the wormhole spacetimes for three particular models for the redshift function. We observe that the null energy condition is violated despite a positive contribution from the electromagnetic energy density. We also note that electric charges, GUP effects, and higher model parameter values increase the throat length. Further, we have studied the deflection of light using the Gauss-Bonnet theorem, emphasizing the contribution from GUP by including higher-order terms.

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arXiv2024

Statistical and Observation Comparison of Weyl-Type $f(Q,T)$ Models with the $Λ$CDM Paradigm

We study the $f(Q,T)$ gravity in the framework of Weyl geometry (known as Weyl-type $f(Q,T)$ gravity), where $Q$ denotes the non-metricity scalar, and $T$ denotes the energy-momentum tensor trace. In this work, we consider the $f(Q,T)$ model, which is defined as $f(Q,T)=αQ^{m+1}+\fracβ{6κ^2}T$ and investigating two scenarios: $(I)$ $m=0$ (linear model) and $(II)$ $m\neq 0$ (nonlinear model). For both scenarios, we find the explicit solution for the field equations by using the barotropic equation of state as $p=wρ$, where $w$ is the equation-of-state (EoS) parameter. Further, we study the obtained solutions statistically using the $Pantheon^+$ (Without SHOES Calibrated) dataset with 1701 data points. For both models, the best-fit values of model parameters for $1-σ$ and $2-σ$ confidence level. The higher Hubble constant values in both models emphasize the presence of Tension. We statistically compare our models to the $Λ$CDM model using ${{\protectχ}^2_{min}}$, ${{\protectχ}^2_{red}}$, $AIC$, $ΔAIC$, $BIC$ and $ΔBIC$. We also examine cosmological parameters such as deceleration and EoS parameters to determine the current acceleration expansion of the Universe. Furthermore, we test our model using $Om$ diagnostic and compare it to the $Λ$CDM model to determine its dark energy profile. Finally, we draw the conclusion that statistically speaking, both linear and nonlinear models show good compatibility with the $Λ$CDM model.

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arXiv2024

Deflection of light by wormholes and its shadow due to dark matter within modified symmetric teleparallel gravity formalism

We explore the possibility of traversable wormhole formation in the dark matter halos in the context of $f(Q)$ gravity. We obtain the exact wormhole solutions with anisotropic matter source based on the Bose-Einstein condensate, Navarro-Frenk-White, and pseudo-isothermal matter density profiles. Notably, we present a novel wormhole solution supported by these dark matters using the expressions for the density profile and rotational velocity along with the modified field equations to calculate the redshift and shape functions of the wormholes. With a particular set of parameters, we demonstrate that our proposed wormhole solutions fulfill the flare-out condition against an asymptotic background. Additionally, we examine the energy conditions, focusing on the null energy conditions at the wormhole's throat, providing a graphical representation of the feasible and negative regions. Our study also examines the wormhole's shadow in the presence of various dark matter models, revealing that higher central densities result in a shadow closer to the throat, whereas lower values have the opposite effect. Moreover, we explore the deflection of light when it encounters these wormholes, particularly noting that light deflection approaches infinity at the throat, where the gravitational field is extremely strong.

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arXiv2024

Influence of GUP corrected Casimir energy on zero tidal force wormholes in modified teleparallel gravity with matter coupling

In recent times, the study of the Casimir effect in quantum field theory has garnered increasing attention because of its potential to be an ideal source of exotic matter needed for stabilizing traversable wormholes. It has been confirmed through experimental evidence that this phenomenon involves fluctuations in the vacuum field, leading to a negative energy density. Motivated by the above, we have investigated Casimir wormholes with corrections from the Generalized Uncertainty Principle (GUP) within the framework of matter-coupled teleparallel gravity. Our analysis includes three well-known GUP models: the Kempf, Mangano, and Mann (KMM) model, the Detournay, Gabriel, and Spindel (DGS) model, and a third model called Model II. For a broader analysis, we have considered two well-known model functions for the teleparallel theory: a linear $f(T,\mathcal{T})=αT+β\mathcal{T}$ and a quadratic model $f(T,\mathcal{T})=ηT^2+χ\mathcal{T}$. The shape function solutions corresponding to both models are examined in the absence of tidal forces in spacetime. We also demonstrate the crucial role played by the parameters of the $f(T,\mathcal{T})$ models in the violation of the energy conditions. With the increasing interest in detecting gravitational waves from astrophysical objects, we have thoroughly discussed the perturbation of the wormhole solutions in the scalar, electromagnetic, axial gravitational, and Dirac field backgrounds. We employ the $3^{rd}$ order WKB expansion to find the complex frequencies associated with the quasinormal modes of energy dissipation. Additionally, we also calculate the active mass and total gravitational energy for the wormhole geometry. The amount of exotic matter involved in sustaining these wormholes is also found in this paper. Furthermore, the physical stability of such Casimir wormholes is examined using the Tolman-Oppenheimer-Volkoff equation.

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arXiv2024

Charged gravastar model in noncommutative geometry under $f(\mathbb{T})$ gravity

In this article, we study the properties of charged gravastars in torsion-based $f(\mathbb{T})$ gravity in the presence of noncommutative geometry. We have taken the interior from noncommutative motivated space-time, noting that why, from a physical point of view, such a choice is justified, then we have taken the thin shell as stiff matter and taken three different exterior metrics (Reissner-Nordstrom (R-N), Bardeen and Ayon-Beato-Garcia (ABG) metric) to construct the gravastar model. We have studied the physical properties like proper length, entropy, energy, and EoS for these models, and we have also used Israel junction conditions to study the effective pressure, energy density, and potential of the thin shell. Finally, we comment on the stability of such a thin shell and the deflection angle caused by such a thin shell, which could, in principle, be tested by future radio telescopes like the Event Horizon Telescope (EHT).

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arXiv2024

Modeling and Analyzing Stability of Hybrid Stars within $f(Q)$ Gravity

This study uses the Krori-Barua type metric to represent hybrid stars within the $f(Q)$ theory of gravity. We postulate that the hybrid star also contains strange quark matter in addition to regular baryonic matter. To investigate the physical viability of the hybrid star model, we present the graphical behavior of the energy density, radial pressure, and tangential pressure, equation of state parameters, anisotropy, and stability analysis, respectively, by choosing the compact star EXO 1785-248 with a mass of $1.3_{-0.2}^{+0.2}~M_{\odot}$ and radius $8.849_{-0.4}^{+0.4}$ km with five different values of the coupling constants as $a=2$, $a=4$, $a=6$, $a=8$, and $a=10$. The maximum allowed masses and corresponding radii have been calculated using the $M-R$ curve for three different coupling parameter '$a$' values which match the observational data of three distinct compact stars, namely LMC X-4, SMC X-1, and 4U 1538-52. So, the $f(Q)$ theory of gravity can provide results that are plausible for describing the macroscopical characteristics of hybrid star candidates.

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arXiv2024

Cosmological constraints on $f(Q)$ gravity models in the non-coincident formalism

The article investigates cosmological applications of $f(Q)$ theories in a non-coincident formalism. We explore a new $f(Q)$ theory dynamics utilizing a non-vanishing affine connection involving a non-constant function $γ(t)=-a^{-1}\dot{H}$, resulting in Friedmann equations that are entirely distinct from those of $f(T)$ theory. In addition, we propose a new parameterization of the Hubble function that can consistently depicts the present deceleration parameter value, transition redshift, and the late time de-Sitter limit. We evaluate the predictions of the assumed Hubble function by imposing constraints on the free parameters utilizing Bayesian statistical analysis to estimate the posterior probability by employing the CC, Pantheon+SH0ES, and the BAO samples. Moreover, we conduct the AIC and BIC statistical evaluations to determine the reliability of MCMC analysis. Further, we consider some well-known corrections to the STEGR case such as an exponentital $f(Q)$ correction, logarithmic $f(Q)$ correction, and a power-law $f(Q)$ correction and then we find the constraints on the parameters of these models via energy conditions. Finally, to test the physical plausibility of the assumed $f(Q)$ models we conduct the thermodynamical stability analysis via the sound speed parameter.

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arXiv2024

On the asymmetric non-canonical braneworld in five dimensions

Revisiting Einstein's gravitational theory, we build a five-dimensional braneworld. Within this framework, one announces the appearance of symmetric and asymmetric domain walls. Furthermore, it examines the emergent four-dimensional gravity from a theory with non-canonical dynamics. Exploring the physical and mathematical aspects, e.g., brane's energy density and the Kaluza-Klein (KK) spectrum, one verifies that brane splitting is absent in the canonical and non-canonical theories. Additionally, we note the localization of the four-dimensional fluctuation projection on the 3-branes, which ensures the theory's stability. Thereby, one can conclude that the behavior of gravitational perturbations of the domain wall maintains a profile similar to a stable and non-localizable tower of massive modes. In contrast, within the brane core, the matter sector generates new barriers and potential wells, resulting in massive modes with approximately symmetric amplitudes. However, the non-canonical dynamics generate massive modes with asymmetric amplitudes far from the 3-brane.

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arXiv2024

Wormhole formations in the galactic halos supported by dark matter models and global monopole charge within $f(Q)$ gravity

This paper discusses the possibility of traversable wormholes in the galactic region supported by dark matter (DM) models and global monopole charge in the context of $f(Q)$ gravity. To understand the features of the wormholes, we comprehensively studied wormhole solutions with various redshift functions under different $f(Q)$ models. We obtained wormhole shape functions for Pseudo Isothermal (PI) and Navarro-Frenk-White (NFW) DM profiles under linear $f(Q)$ gravity. In contrast, we employed an embedding class I approach for the non-linear $f(Q)$ models to investigate wormholes. We noticed that our obtained shape functions satisfy the flare-out conditions under an asymptotic background for each DM profile. Moreover, we checked the energy conditions at the wormhole throat with a radius $r_0$ and noticed the influences of the global monopole's parameter $η$ in the violation of energy conditions, especially null energy conditions. Further, for the non-linear case, we observed that wormhole solutions could not exist for $f(Q)=Q+mQ^n$, $f(Q)=Q+\fracβ{Q}$, and $f(Q)=α_1+β_1 \log(Q)$ under embedding class I approach. Finally, we study the amount of exotic matter via the volume integral quantifier technique for the linear $f(Q)$ model, and we confirm that a small amount of exotic matter is required to sustain the traversable wormholes.

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arXiv2024

Investigating early and late-time epochs in $ f(Q) $ gravity

In the following work, a new hybrid model of the form $ f(Q)=Q(1+a)+b\frac{Q_0^2}{Q} $ has been proposed and confronted using both early as well as late-time constraints. We first use conditions from the era of Big Bang Nucleosynthesis (BBN) in order to constrain the models which are further used to study the evolution of the Universe through the deceleration parameter. This methodology is employed for the hybrid model as well as a simple model of the form $ α_1 Q+α_2 Q_0 $ which is found to reduce to $Λ$CDM. The error bar plot for the Cosmic Chronometer (CC) and Pantheon+SH0ES datasets which includes the comparison with $Λ$CDM, has been studied for the constrained hybrid model. Additionally, we perform a Monte Carlo Markov Chain (MCMC) sampling of the model against three datasets -- CC, Pantheon+SH0ES, and Baryon Acoustic Oscillations (BAO) to find the best-fit ranges of the free parameters. It is found that the constraint range of the model parameter ($a$) from the BBN study has a region of overlap with the ranges obtained from the MCMC analysis. Finally, we perform a statistical comparison between our model and the $Λ$CDM model using AIC and BIC method.

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arXiv2024

Wormhole Geometries Supported by Strange Quark Matter and Phantom-like Generalized Chaplygin gas within $f(Q)$ Gravity

A crucial aspect of wormhole (WH) physics is the inclusion of exotic matter, which requires violating the null energy condition. Here, we explore the potential for WHs to be sustained by quark matter under conditions of extreme density along with the phantom-like generalized cosmic Chaplygin gas (GCCG) in symmetric teleparallel gravity. Theoretical and experimental studies on baryon structures indicate that strange quark matter, composed of u (up), d (down), and s (strange) quarks, represents the most energy-efficient form of baryonic matter. Drawing from these theoretical insights, we use the Massachusetts Institute of Technology (MIT) bag model equation of state to characterize ordinary quark matter. By formulating specific configurations for the bag parameter, we develop several WH models corresponding to different shape functions for the isotropic and anisotropic cases. Our analysis strongly suggests that an isotropic WH is not theoretically possible. Furthermore, we investigate traversable WH solutions utilizing a phantom-like GCCG, examining their feasibility. This equation of state, capable of violating the null energy condition, can elucidate late-time cosmic acceleration through various beneficial parameters. In this framework, we derive WH solutions for both constant and variable redshift functions. We have employed the volume integral quantifier (VIQ) method for both studies to assess the quantity of exotic matter. Furthermore, we have done the equilibrium analysis through the Tolman-Oppenheimer-Volkoff (TOV) equation, which supports the viability of our constructed WH model.

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arXiv2024

Reconstruction of the singularity-free $f(\mathcal{R})$ gravity via Raychaudhuri equations

We study the bounce cosmology to construct a singularity-free $f(\mathcal{R})$ model using the reconstruction technique. The formulation of the $f(\mathcal{R})$ model is based on the Raychaudhari equation, a key element employed in reconstructed models to eliminate singularities. We explore the feasibility of obtaining stable gravitational Lagrangians, adhering to the conditions $f_{\mathcal{R}}>0$ and $f_{\mathcal{R}\mathcal{R}}>0$. Consequently, both models demonstrate stability, effectively avoiding the Dolgov-Kawasaki instability. Our assessment extends to testing the reconstructed model using energy conditions and the effective equation-of-state (EoS). Our findings indicate that the reconstructed super-bounce model facilitates the examination of a singularity-free accelerating universe for both phantom and non-phantom phases. However, in the case of the reconstructed oscillatory bounce model, two scenarios are considered with $ω=-1/3$ and $ω=-2/3$. While the model proves suitable for studying a singular-free accelerating universe in the $ω=-1/3$ case, it fails to demonstrate such behavior under energy conditions for the $ω=-2/3$ scenario. The reconstructed models accommodate early-time bouncing behavior and late-

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arXiv2024

Gaussian Process Approach for Model-Independent Reconstruction of $f(Q)$ Gravity with Direct Hubble Measurements

The increase of discrepancy in the standard procedure to choose the arbitrary functional form of the Lagrangian $f(Q)$ motivates us to solve this issue in modified theories of gravity. In this regard, we investigate the Gaussian process (GP), which allows us to eliminate this issue in a $f(Q)$ model-independent way. In particular, we use the 57 Hubble measurements coming from cosmic chronometers and the radial Baryon acoustic oscillations (BAO) to reconstruct $H(z)$ and its derivatives $H'(z)$, $H''(z)$, which resulting lead us to reconstruct region of $f(Q)$, without any assumptions. The obtained mean curve along $Λ$CDM constant in the reconstructed region follows a quadratic behavior. This motivates us to propose a new $f(Q)$ parametrization, i.e., $f(Q)= -2Λ+ εQ^2$, with the single parameter $ε$, which signifies the deviations from $Λ$CDM cosmology. Further, we probe the widely studied power-law and exponential $f(Q)$ models against the reconstructed region and can improve the parameter spaces significantly compared with observational analysis. In addition, the direct Hubble measurements, along with the reconstructed $f(Q)$ function, allow the $H_0$ tension to be alleviated.

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arXiv2024

Dynamical system analysis of Dirac-Born-Infeld scalar field cosmology in coincident $f(Q)$ gravity

In this article, we offer the dynamical system analysis of the DBI (Dirac-Born-Infeld) scalar field in a modified $f(Q)$ gravity context. We have taken a polynomial form of modified gravity and used two different kinds of scalar potential, i.e., polynomial and exponential, and found a closed autonomous dynamical system of equations. We have analyzed the fixed points of such a system and commented on the conditions under which deceleration to late-time acceleration happens in this model. We have noted the similarity of the two models and have also shown that our result is indeed consistent with the previous work done on Einstein's gravity. We have also investigated the phenomenological implications of our models by plotting the EoS ($ω$), Energy density ($Ω$), and deceleration parameter ($q$) w.r.t. to e-fold time and comparing with the present value. Finally, we conclude the paper by observing how the dynamical system analysis differs in modified $f(Q)$ gravity, and we also provide some of the future scope of our work.

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arXiv2024

Can $f(T)$ models play a bridge between early and late time Universe?

The ability of Big Bang Nucleosynthesis theory to accurately predict the primordial abundances of helium and deuterium, as well as the baryon content of the Universe, is considered one of the most significant achievements in modern physics. In the present study, we consider two highly motivated hybrid $f(T)$ models and constrain them using the observations from the Big Bang Nucleosynthesis era. In addition, using late-time observations of Cosmic Chronometers and Gamma-Ray-Bursts, the ranges of the model parameters are confined which are in good agreement with early time bounds. Subsequently, the common ranges obtained from the analysis for early and late time are summarized. Further, we verify the intermediating epochs by investigating the profiles of cosmographic parameters using the model parameter values from the common range. From this study, we find the considered teleparallel models are viable candidates to explain the primordial-intermediating-present epochs.

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arXiv2024

Bulk viscous cosmological model in $f(T,\mathcal{T})$ modified gravity

This article explores the impact of bulk viscosity on understanding the universe's accelerated expansion within the context of modified $f(T,\mathcal{T})$ gravity, which is an extension of the $f(T)$ gravitational theory, allowing a broad coupling between the energy-momentum scalar $\mathcal{T}$ and the torsion scalar $T$. We consider two $f(T,\mathcal{T})$ functions, specifically $f(T,\mathcal{T})=αT + β\mathcal{T}$ and $f(T,\mathcal{T})=α\sqrt{-T} + β\mathcal{T}$, where $α$ and $β$ are arbitrary constants, along with the fluid part incorporating the coefficient of bulk viscosity $ζ=ζ_0 > 0$. We calculate the analytical solutions of the corresponding field equations for a flat FLRW environment, and then we constrain the free parameters of the obtained solution using CC, Pantheon+, and the CC+Pantheon+ samples. We perform the Bayesian statistical analysis to estimate the posterior probability utilizing the likelihood function and the MCMC random sampling technique. Further, to assess the effectiveness of our MCMC analysis, we estimate the corresponding AIC and BIC values, and we find that there is strong evidence supporting the assumed viscous modified gravity models for all three data sets. Also, we find that the linear model precisely mimics the $Λ$CDM model. We also investigate the evolutionary behavior of some prominent cosmological parameters. We observe that the effective equation of state parameter for both models predict the accelerating behavior of the cosmic expansion phase. In addition, from the statefinder test, we find that the parameters of the considered MOG models favor the quintessence-type behavior.

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