arXiv subjects

P. K. Sahoo

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

At least 19 recordsLinked to original sources

arXiv2026

Observational Signatures of Static and Rotating Wormholes Embedded in Dark Matter

We study static and slowly rotating traversable wormholes embedded in two contrasting dark matter environments, the cuspy Navarro-Frenk-White (NFW) halo and the cored solitonic wave dark matter ($\psi$DM) profile, using observational parameters set by the rotation curve of the dwarf galaxy NGC\,2366. For each profile, we solve the Einstein field equations in the Morris-Thorne framework to obtain the shape and redshift functions, then extend to slow rotation via the Teo metric with a Lense--Thirring frame-dragging term. Across the four resulting spacetimes and six throat radii, we trace null geodesics, compute specific intensity profiles and polar shadow maps, and construct accretion disk images including the full relativistic Doppler effect. We noticed these two profiles differ sharply in photon dynamics. The NFW potential is too shallow to support a detached photon sphere, so its critical impact parameter stays close to the throat radius. The soliton core, by contrast, is focused enough to host a genuine unstable photon orbit that raises the critical impact parameter to about $1.18$--$1.26$ times the throat radius. This difference in photon-sphere structure propagates through nearly every observable, including photon-ring sharpness, shadow size, accretion-disk appearance, and, in the rotating case, the degree of shadow asymmetry from frame dragging. The soliton shadow size also tracks the mass of the underlying ultralight boson through $\rho_c\propto m_b^{-2}$, with a transition from total capture to mainly deflecting lensing near $m_b\sim10^{-18}$\,eV, a feature absent for NFW that offers a direct probe of dark matter microphysics. These results show that wormhole photon dynamics are shaped by the dark matter profile, pointing to a possible observational route to probe the nature of dark matter.

gr-qc↗

arXiv2026

Reconstruction of a dark energy model for the Dirac-Born-Infeld scalar field with the Hubble and DESI data via Gaussian process

In this study, we reconstruct the dark energy (DE) as a Dirac-Born-Infeld (DBI) scalar field from the Hubble dataset (32 CC + 26 BAO) and the DESI dataset using the Gaussian process (GP). As the GP is a non-parametric and model-independent way to reconstruct a function and its derivative using the data, our reconstruction of the DE equation of state, the DE density parameter, and the potential does not assume any particular model of cosmology. Using Monte Carlo realizations of the GP-reconstructed expansion history, we derive a posterior estimate of the Hubble constant, obtaining $H_0 = 69.53 \pm 2.68$ km s$^{-1}$ Mpc$^{-1}$. This method offers a fully model-independent estimate of $H_0$, relying only on data and GP priors, and provides an unbiased intermediate value useful for reassessing the Planck-SH0ES tension. Using the reconstructed profiles of the scalar potential as a function of the field $\phi$, along with their associated uncertainties, we perform a chi-square curve fitting procedure to assess the viability of four different scalar field potentials, such as Exponential, Power-law, Free Field (quadratic), and Higgs-like potential. This allows us to identify which potential best fits the reconstructed data. We also employ MCMC analysis to place quantitative constraints on the model parameters associated with each potential. Furthermore, we do a $\chi^2$ analysis for all four potentials and comment on the goodness of the fit for each of them. Finally, we discuss possible generalizations of our model-independent framework and outline the phenomenological implications of our findings.

physics.gen-ph↗

arXiv2026

Kinematic Probes of Type-II MMG: Pad\'e Cosmographic Analysis of VCDM

We study the late-time expansion history of the Universe within the VCDM model, a Type-II MMG realization that preserves the successes of General Relativity while extending beyond constant vacuum energy through a minimal Hamiltonian modification, generating a time-dependent vacuum sector without introducing additional degrees of freedom. We investigate this framework within a cosmographic approach by employing a Pad\'e $P_{(2,1)}$ approximation for the Hubble parameter and luminosity distance, allowing the cosmographic parameters to be expressed directly in terms of the underlying VCDM model parameters and enabling a data-driven reconstruction of the expansion history. The model is constrained within a Bayesian framework using the MCMC technique, implemented via the affine-invariant ensemble sampler, with a joint analysis of cosmic chronometers, DESI BAO, and Type Ia supernova datasets (Union3, Pantheon+, and DESY5). We find that the model parameters are tightly constrained and consistent across different dataset combinations, with the jerk parameter remaining very close to its $\Lambda$CDM value, $j_0 \simeq 1$, indicating no significant deviation at the level of higher-order cosmography. Furthermore, the transition feature previously reported in VCDM is not observed within the Pad\'e $P_{(2,1)}$ cosmographic reconstruction, suggesting that it is not a robust requirement of current observational data but is sensitive to the choice of parametrization. Overall, our results indicate that the VCDM model effectively mimics $\Lambda$CDM at the background level when constrained through a cosmographic approach, underscoring the importance of model-independent reconstructions in assessing alternative cosmological scenarios.

physics.gen-ph↗

arXiv2026

The Amplitude-Growth Degeneracy and Implied $A_s$ Diagnostic for Background-Inert Modified Gravity

We prove that any background-inert perturbative coupling $ \lambda $ in coincident $ f(Q) $ gravity exhibits a degeneracy with the clustering amplitude $ \sigma_{80} $, when using compressed CMB distance priors. This degeneracy is, in fact, a direct materialization of a deeper $ A_s-D_0(\lambda) $ degeneracy between the primordial amplitude $ A_s $ and the present day growth factor $ D_0(\lambda) $. We outline a consistency check scheme, whose logic extends to any model in which the coupling is background inert, by computing $ A_s $ per posterior sample, needed to reproduce the $ \sigma_{80} $ preferred by the sampler. We perform our analysis with two dataset pipelines, based on the coupled/decoupled $ f\sigma_8(z) $ data. To ensure theoretical diversity, we include $ \Lambda $CDM and the Hybrid model in the $ f(Q) $ framework. Our results illustrate that adding the $ \lambda_0\sqrt{QQ_0} $ correction to the models inflates $ \sigma_{80} $ by $ 5\%-8\% $ as compared to its vanilla variant, while the Bayesian evidence disfavors every alternative considered - $\Delta\log\mathcal{Z} = -0.5$ to $-2.6$ against $\Lambda$CDM on the same pipeline. Propagating this inflated $ \sigma_{80} $ through a per-sample computation of the implied primordial amplitude accounting for both the transfer function and the modified growth factor yields $\ln(10^{10}A_s)$ in $1.5\sigma-2.6\sigma$ tension with Planck 2018. Imposing the $ \ln(10^{10}A_s) $ constraint from Planck 2018 as an additional prior removes this inflation, pulling $ \sigma_{80} $ to the Planck value and $ \lambda_0 $ to values consistent with $ 0 $, with the implied amplitude recovering to within $ 0.2\sigma $ of Planck in every case. We find no model-dataset combination preferred over $ \Lambda $CDM.

astro-ph.CO↗

arXiv2026

Beyond the Cosmological Constant: Breaking the Geometric Degeneracy of $ f(Q) $ cosmology via Redshift-Space Distortions

We present a rigorous theoretical and observational analysis of the Hybrid $ f(Q) $ class of models by including the late-time modifying $ 1/Q $ term. After deriving strict viability conditions from the analytical expansion history, we show that preserving early-universe structure formation dictates that the linear coupling be exactly unity. This fixes the background of the Hybrid model into a geometric degeneracy with $ \Lambda $CDM which is confirmed explicitly through MCMC analysis with the latest background-only probes. The physical novelty of this model is manifest in the perturbation sector, where the geometric coupling breaks the background degeneracy and induces a late-time suppression of the effective gravitational constant $ G_{eff} < G_N $. Consequently, the inclusion of RSD data reveals an amplitude compensation mechanism, by which the matching of the signature $ f\sigma_8 $ of the data causes the clustering amplitude $ \sigma_8 $ to inflate under weaker gravity. Statistical model comparison through AIC/DIC demonstrates that incorporating growth data yields a moderate to weak preference for the Hybrid model keeping the background cosmology intact. This provides a physically bounded alternative to $ \Lambda $CDM with a falsifiable signature in the large scale structure, directly testable by the next generation of galaxy surveys.

gr-qc↗

arXiv2026

Exploring Late-Time Cosmic Acceleration in VCDM Cosmology

In this work, we have considered a minimally modified gravity theory that effectively reproduces VCDM-like behavior to investigate its cosmological implications. The model parameters are constrained using a combination of CC, RSD, DESI BAO DR2, and Union3 datasets. The model parameters are constrained using an MCMC framework, ensuring a robust estimation of credible intervals. We examine both background and perturbation-level observables, analyzing the Hubble parameter, deceleration parameter, effective equation of state, distance modulus, and the growth rate of cosmic structures through the $fσ_8(z)$ observable. Our results show that the model successfully reproduces the observed expansion history, featuring a smooth transition in the Hubble evolution around $z \simeq 0.3$, and consistent behaviour of cosmological parameters. The model outperforms $Λ$CDM in the statistical comparisons for the full dataset combination (CC+RSD+DESI DR2+Union3). These results highlight the potential of minimally modified gravity theories with VCDM-like dynamics as consistent and competitive alternatives to the standard cosmological paradigm.

astro-ph.CO↗

arXiv2026

BBN to Late-Time Acceleration in $f(T,\mathcal{L}_m)$ Gravity

We present, to our knowledge, the first systematic study of early-late cosmic evolution and acceleration in the framework of $f(T,\mathcal{L}_m)$ gravity, an extension of teleparallel theories coupling torsion with the matter Lagrangian. By incorporating the Big-Bang Nucleosynthesis (BBN) bound on the freeze-out temperature, we obtain a tight constraint on the inverse-torsion parameter, ensuring consistency with early-time physics. Employing Markov Chain Monte Carlo analyses with progressively richer observational datasets, CC, Union3, and SN22 supernovae, we constrain a well-motivated model and reconstruct key cosmological functions. The reconstructed Hubble and distance modulus functions show excellent agreement with the observations, confirming the observational viability of the model. The model successfully reproduces the observed late-time expansion history, yielding a transition from deceleration to acceleration through the deceleration parameter. The effective equation of state is found to remain negative throughout, with present values $w_0 > -1$, indicating a quintessence-like behavior rather than a cosmological constant or phantom regime. These results highlight the ability of $f(T,\mathcal{L}_m)$ gravity to mimic the concordance scenario while allowing controlled deviations in the expansion history.

gr-qc↗

arXiv2026

Observational constraints on viscous free-$γ$ fluid in $f(Q)$ gravity

We study the late-time cosmological dynamics of a spatially flat FLRW universe in the framework of $f(Q)$ gravity, where $Q$ denotes the nonmetricity scalar. The matter sector is modeled as a bulk viscous fluid with a free equation-of-state parameter $γ$, allowing for a generalized description of cosmic matter beyond the standard dust approximation. We derive the background evolution equations and analyze the resulting expansion history. The model parameters are constrained using a combination of observational datasets, including cosmic chronometers (CC), baryon acoustic oscillations from DESI DR2, and Type~Ia supernovae (GRBs and Union3). Using the best-fit parameters, we further employ the statefinder and $\mathrm{Om}(z)$ diagnostics to distinguish the viscous $f(Q)$ scenario from the standard $Λ$CDM model. In addition, we examine the evolution of the deceleration parameter, which exhibits a transition from an early decelerated phase to the current accelerated expansion, and analyze the effective equation of state behavior. Our results show that bulk viscosity within $f(Q)$ gravity provides a viable and observationally consistent description of late-time cosmic acceleration.

gr-qc↗

arXiv2026

Bayesian Inference of Neutron Star Properties in $f(Q)$ Gravity Using NICER Observations

In this work, we investigate neutron stars (NSs) in the strong field regime within the framework of symmetric teleparallel $f(Q)$ gravity, considering three representative models: linear, logarithmic, and exponential. While Bayesian studies of NS observations are well established in general relativity and curvature based modified gravity theories, such analyses in $f(Q)$ gravity remain largely unexplored. For the first time we perform a Bayesian inference analysis by confronting theoretical NS mass-radius predictions with NICER observations of PSR J0030+0451, PSR J0740+6620, PSR J0437+4715, and PSR J0614+3329 in the background of nonmetricity based gravity. The dense matter equation of state is fixed to DDME2 in order to isolate the effects of modified gravity on NS structure. Our results show that the exponential $f(Q)$ model is statistically preferred over the linear and logarithmic cases, as confirmed by Bayes factor comparisons, and exhibits well-constrained. For this model, we obtain a radius and tidal deformability at $1.4\,M_\odot$ of $R_{1.4} = 11.27^{+0.53}_{-0.36}\,\mathrm{km}$ and $\Lambda_{1.4} = 156.95^{+84.02}_{-41.73}$, respectively, consistent with current observational constraints. Remarkably, all three constrained models predict maximum neutron star masses reaching $M_{\max} \simeq 2.98\,M_{\odot}$, with the $95\%$ confidence regions extending into the lower mass gap ($\sim 2.5$--$5\,M_{\odot}$). This mass-gap prediction emerges naturally from the Bayesian-constrained parameter space. These results highlight the potential of NSs as powerful probes of symmetric teleparallel gravity in the strong field regime.

gr-qc↗

arXiv2025

2D Excitonics with Atomically Thin Lateral Heterostructures

Semiconducting transition metal dichalcogenides (TMDs), such as MoSe$_2$ and WSe$_2$, exhibit unique optical and electronic properties. Vertical stacking of layers of one or more TMDs, to create heterostructures, has expanded the fields of moiré physics and twistronics. Bottom-up fabrication techniques, such as chemical vapor deposition, have advanced the creation of heterostructures beyond what was possible with mechanical exfoliation and stacking. These techniques now enable the fabrication of lateral heterostructures, where two or more monolayers are covalently bonded in the plane of their atoms. At their atomically sharp interfaces, lateral heterostructures exhibit additional phenomena, such as the formation of charge-transfer excitons, in which the electron and hole reside on opposite sides of the interface. Due to the energy landscape created by differences in the band structures of the constituent materials, unique effects such as unidirectional exciton transport and excitonic lensing can be observed in lateral heterostructures. This review outlines recent progress in exciton dynamics and spectroscopy of TMD-based lateral heterostructures and offers an outlook on future developments in excitonics in this promising system.

cond-mat.mtrl-sci↗

arXiv2025

$f(Q,L_m)$ gravity, and its cosmological implications

Symmetric teleparallel gravity and its $f(Q)$ extensions have emerged as promising alternatives to General Relativity (GR), yet the role of explicit geometry-matter couplings remains largely unexplored. In this work, we address this gap by proposing a generalized $f(Q,\mathcal{L}_m)$ theory, where the gravitational Lagrangian density depends on both the non-metricity scalar $Q$ and the matter Lagrangian $\mathcal{L}_m$. This formulation naturally includes Coincident GR and the Symmetric Teleparallel Equivalent of GR as special cases. Working in the metric formalism, we derive the corresponding field equations, which generalize those of the standard $f(Q)$ gravity, and obtain the modified Klein-Gordon equation for scenarios involving scalar fields. The cosmological implications of the theory are explored in the context of the Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. As a first step, we obtain the modified Friedmann equations for $f(Q,\mathcal{L}_m)$ gravity in full generality. We then investigate specific cosmological models arising from both linear and non-linear choices of $f(Q,\mathcal{L}_m)$, performing detailed comparisons with the standard $Λ$CDM scenario and examining their observational consequences.

gr-qc↗

arXiv2025

Cosmology in energy-momentum squared symmetric teleparallel gravity

In this letter, we explore the $f(Q,T_{μν}T^{μν})$ gravity theory, building upon the foundations laid by the $f(Q)$ and $f(Q,T)$ gravity theories. Here, $Q$ represents non-metricity and $T_{μν}$ stands for the energy-momentum tensor. The proposed action encompasses an arbitrary function of both non-metricity $Q$ and the square of the energy-momentum tensor, specifically $T^2=T_{μν}T^{μν}$. We find the analytical solution for the barotropic fluid case $p=ωρ$ for the model $f(Q, T_{μν}T^{μν}) = Q + η(T_{μν}T^{μν}) $. We constrain parameters of the solution $H(z)$ utilizing CC, BAO, and latest Pantheon+SH0ES samples with the help of Monte Carlo Markov Chain sampling technique along with Bayesian statistical analysis. Further, from the Om diagnostic test, we find that the assumed cosmological model favors the quintessence regime.

gr-qc↗

arXiv2025

A Study of stable wormhole solution with non-commutative geometry in the framework of linear $f(R,\mathcal{L}_m, T)$ gravity

This research delves into the potential existence of traversable wormholes (WHs) within the framework of modified, curvature based gravity. The modification includes linear perturbations of the matter Lagrangian and the trace of the energy-momentum tensor with specific coupling strengths $α$ and $β$ and can thus be viewed as a special case of linear $f(R,T)$-gravity with a variable matter coupling or as the simplest additively separable $f(R,\mathcal{L}_m,T)$-model. A thorough examination of static WH solutions is undertaken using a constant redshift function; therefore, our work can be regarded as the first-order approximation of WH theories in $f(R,\mathcal{L}_m,T)$ . The analysis involves deriving WH shape functions based on non-commutative geometry, with a particular focus on Gaussian and Lorentzian matter distributions $ρ$. Constraints on the coupling parameters are developed so that the shape function satisfies both the flaring-out and asymptotic flatness conditions. Moreover, for positive coupling parameters, violating the null energy condition (NEC) at the WH throat $r_0$ demands the presence of exotic matter. For negative couplings, however, we find that exotic matter can be avoided by establishing the upper bound $β+α/2<-\frac{1}{ρr_0^2}-8π$. Additionally, the effects of gravitational lensing are explored, revealing the repulsive force of our modified gravity for large negative couplings. Lastly, the stability of the derived WH solutions is verified using the Tolman-Oppenheimer-Volkoff (TOV) formalism.

gr-qc↗

arXiv2025

Derivation of the deformed Heisenberg algebra from discrete spacetime

Although the deformation of the Heisenberg algebra by a minimal length has become a central tool in quantum gravity phenomenology, it has never been rigorously obtained and is often derived using heuristic reasoning. In this study, we move beyond the heuristic derivation of the deformed Heisenberg algebra and explicitly derive it using a model of discrete spacetime, which is motivated by quantum gravity. Initially, we investigate the effects of the leading order Planckian lattice corrections and demonstrate that they precisely match those suggested by the heuristic arguments commonly used in quantum gravity phenomenology. Furthermore, we rigorously obtain deformations from the higher-order Planckian lattice corrections. In contrast to the leading-order corrections, these higher-order corrections are model dependent. We select a specific model that breaks the rotational symmetry, as the importance of such rotational symmetry breaking lies in the relationship between CMB anisotropies and quantum gravitational effects. Based on the mathematical similarity of the Planckian lattice used here with the graphene lattice, we propose that graphene can serve as an analogue system for the study of quantum gravity. Finally, we examine the deformation of the covariant form of the Heisenberg algebra using a four-dimensional Euclidean lattice.

gr-qc↗

arXiv2025

The Stability of Anisotropic Compact Stars Influenced by Dark Matter under Teleparallel Gravity: An Extended Gravitational Deformation Approach

In our investigation, we pioneer the development of geometrically deformed strange stars within the framework of teleparallel gravity theory through gravitational decoupling via the complete geometric deformation (CGD) technique. The significant finding is the precise solution for deformed strange star (SS) models achieved through the vanishing complexity factor scenario. Further, we introduce the concept of space-time deformation caused by dark matter (DM) content in DM haloes, leading to perturbations in the metric potentials $g_{tt}$ and $g_{rr}$ components. Mathematically, this DM-induced deformation is achieved through the CGD method, where the decoupling parameter $α$ governs the extent of DM influence. To validate our findings, we compare our model predictions with observational constraints, including GW190814 (with a mass range of $2.5-2.67 M_{\odot}$) and neutron stars (NSTRs) such as EXO 1785-248 [mass=$1.3_{-0.2}^{+0.2}~M_{\odot}$], 4U 1608-52 [mass=$1.74_{-0.14}^{+0.14}~M_{\odot}$], and PSR J0952-0607 [mass=$2.35_{-0.17}^{+0.17}~M_{\odot}$]. Our investigation delves into the stability of the model by considering causality conditions, Herrera's Cracking Method, the adiabatic index, and the Harrison-Zeldovich-Novikov criterion. We demonstrate that the developed model mimics a wide range of recently observed pulsars. To emphasize its compatibility, we highlight the predicted mass and radius in tabular form by varying both the parameters $α$ and $ζ_1$. Notably, our findings are consistent with the observation of gravitational waves from the first binary merger event. Furthermore, we compare our results with those obtained for a slow-rotating configuration. In addition to this, we discuss the moment of inertia using the Bejger-Haensel approach in this formulation.

gr-qc↗

arXiv2025

Cosmological dynamics of interacting dark energy and dark matter in $f(Q)$ gravity

In this work, we explore the behavior of interacting dark energy and dark matter within a model of $f(Q)$ gravity, employing a standard framework of dynamical system analysis. We consider the power-law $f(Q)$ model incorporating with two different forms of interacting dark energy and dark matter: $3αHρ_m$ and $\fracα{3H}ρ_m ρ_{DE}$. The evolution of $Ω_m, Ω_r, Ω_{DE}, q$, and $ω$ for different values of the model parameter $n$ and the interaction parameter $α$ has been examined. Our results show that the universe was dominated by matter in the early stages and will be dominated by dark energy in later stages. Using the observational data, the fixed points are found to be stable and can be represented the de Sitter and quintessence acceleration solutions. We discover that the dynamical profiles of the universe in $f(Q)$ dark energy models are influenced by both the interaction term and the relevant model parameters.

gr-qc↗

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.

gr-qc↗

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.

gr-qc↗