arXiv subjects

Mushtaq Ahmad

Publications and source records attributed to Mushtaq Ahmad.

15 recordsLinked to original sources

arXiv2026

C-infinity Compact-Support Wormholes with Exact Schwarzschild Exterior in Trace-Coupled Gravity

We study static, spherically symmetric traversable wormholes in trace-coupled gravity with action density f(R,T) = R + lambda T^2. The spacetime is built from C-infinity deformations of Schwarzschild that vanish identically outside a finite core, so the exterior is exactly Schwarzschild and no thin shell or junction surface is needed. Because f_R = 1, the metric equations remain second order and the matter problem reduces to a local algebraic reconstruction. For an anisotropic source, we derive unified inversion formulas for (rho, p_r, p_t) in terms of the effective source and the dimensionless trace variable chi = lambda T/(4 pi), and show that the admissible matter branch is the vacuum-connected real root of a cubic equation. The resulting parameter space contains regular positive-density and negative-density throat regimes, a critical boundary where the reconstruction degenerates, and a nonadmissible branch-failure sector. The geometry itself is branch-independent, but the reconstructed matter depends on the matter-Lagrangian prescription. On the admissible branch the radial NEC still fails at the throat, so the model localizes exoticity rather than removing it. The Ricci support and reconstructed matter remain confined to a finite interval, while the exterior tidal field is exactly Schwarzschild with ADM mass M. The results should be read as controlled existence and viability statements within the displayed ansatz families, not as a stability proof.

gr-qc↗

arXiv2026

Odd-parity perturbations of trace-quadratic $f(R,T)$ black holes with anisotropic matter: admissible branches, axial ringdown, and a coupled-PINN benchmark

We study odd-parity gravitational perturbations of static black holes in trace-quadratic $f(R,T)=R+αT^2$ gravity supported by an anisotropic effective fluid with constant closure parameters $(w_r,w_t)$. From the unreduced axial system and its principal symbol, we identify the sector of parameter space that supports a regular horizon, asymptotic flatness, and hyperbolic odd-sector evolution. Within this closure the admissible branch lies at negative $w_r$, while the commonly used positive-$w_r$ family fails the background regularity test and is kept only as a numerical comparison branch. On static admissible backgrounds the odd sector is exactly equivalent to Einstein gravity coupled to a frozen effective anisotropic fluid, so the physical axial spectrum is governed by a single gauge-invariant master equation. For the anchored branch $(w_r,w_t)=(-0.2,0.15)$ we compute the fundamental axial $\ell=2$ quasinormal mode with an exact Chebyshev solve. The mass-normalized spectrum differs from Schwarzschild by about $22\%$, whereas no statistically resolved direct $α$-dependence appears within the conservative spectral envelope over $0\le α/M^2\le 0.3$. We also construct a coupled physics-informed neural network for the unreduced two-field eigenproblem and use it to benchmark the inadmissible comparison branch. A closure-level audit of the anchored family shows positive diagnostic combinations associated with the null, weak, and dominant energy conditions, denominator safety in the modified balance law, and an effective exterior mass fraction of about $20\%$, while indicating that the constant-$(w_r,w_t)$ model should be read as an effective anisotropic stress rather than as a microphysical fluid. Within this closure, the main observable imprint in axial ringdown comes from the existence of the matter-supported branch itself, not from direct variation of the trace coupling.

gr-qc↗

arXiv2026

A cosmology-to-ringdown EFT consistency map for scalar-tensor gravity

We construct an effective-field-theory bridge from late-time scalar-tensor cosmology to black-hole ringdown observables. Starting from a cosmology-conditioned EFT posterior, we lift Jordan-frame FLRW data through a finite covariant jet, transport the result to the arbitrary-background EFT for black-hole perturbations with a timelike scalar, and project it onto parity-resolved quasinormal-mode response kernels. The cosmological layer is a deterministic compressed likelihood built from BAO-like distances, growth summaries, low-redshift tensor-speed information, stability filters, and posterior samples for the ringdown pushforward. The detector layer uses Bayesian time-domain injections, one-, two-, and three-mode recovery models, analytic marginalization over linear sine/cosine amplitudes, remnant-calibration covariance products, and start-time variations. The transported posterior shows that FLRW tensor-speed deformations inherited from cosmology are driven far below ringdown detectability, whereas operators that vanish on homogeneous FLRW backgrounds can remain active in the anisotropic near zone of a black hole. For a literature-calibrated Hayward branch, we specify the prior measure, separate directly admissible points from a proxy continuation, and propagate both to detector-whitened consistency modes. The resulting framework turns cosmological viability into black-hole spectroscopy priors while keeping the strong-field completion explicit rather than assumed.

gr-qc↗

arXiv2023

Ricci Inverse Anisotropic Stellar Structures

This paper offers novel quintessence compact relativistic spherically symmetrical anisotropic solutions under the recently developed Ricci inverse gravity Amendola et al., 2020), by employing Krori and Barua gravitational potentials, $Ar^2=ν(r), ~\&~Br^2+C=μ(r)$ (with A, B, and C being real constants). For this objective, a specific explicit equation of state, connecting energy density and radial pressure, i.e., $p_r=ωρ$, such that $0<ω<1$, has been utilized with an anisotripic fluid source. Ricci inverse field equations are used to find the exclusive expressions of the energy density, radial and tangential stresses, and the quintessence energy density, the critical physical attributes reflecting the exceptional conduct of extremely dense matter configuration. For the observatory source stars $Her X-1$, $SAX J 1808.4-3658$ and $4U 1820-30$, all the important physical quantities like energy densities, tangential and radial pressures, energy conditions, gradients, anisotropy, redshift and mass-radius functions, and stellar compactness have been worked out and analyzed graphically. It has been concluded that all of the stellar formations under consideration remain free from any undesirable central singularity and are stable.

gr-qc↗

arXiv2023

$f(\mathcal{G},\mathrm{\textit{T}})$ Gravity Bouncing Universe with Cosmological Parameters

In recent few years, the Gauss-Bonnet $f(\mathcal{G},\mathrm{\textit{T}})$ theory of gravity has fascinated considerable researchers owing to its coupling of trace of the stress-energy tensor $T$ with the Gauss-Bonnet term $\mathcal{G}$. In this context, we focuss ourselves to study bouncing universe with in $f(\mathcal{G},\mathrm{\textit{T}})$ gravity background. Some important preliminaries are presented along with the discussion of cosmological parameters to develop a minimal background about $f(\mathcal{G},\mathrm{\textit{T}})$ theory of gravity. The exact bouncing solutions with physical analysis are provided with the choice of two equation of state parameters. It is shown that the results do agree with the present values of deceleration, jerk and snap parameters. Moreover, it is concluded that the model parameters are quite important for the validity of conservation equation (as the matter coupled theories do not obey the usual conservation law).

gr-qc↗

arXiv2021

Charged Anisotropic Finch-Skea-Bardeen Spheres

This manuscript explores the compact geometries by employing Karmarkar condition with the charged anisotropic source of matter distribution. For this purpose, we consider an explicit model by indulging $\mathrm{g}_{rr}$ metric potential obeying the Karmarkar condition. Moreover, we ansatz the time metric co-efficient following the approach by Adler. The crucial aspect of present investigation is the implication of the Bardeen model as an outer spacetime. Implementation of Bardeen approach turns out to be very interesting as this corresponds to the magnetic mono-pole gravitational remnants emerging from some particular non-linear electrodynamics. Detailed analysis supported by their corresponding plots of the profiles of the pressure profiles, energy density, charged density, anisotropy function, electric field attributes, energy bounds, redshift function, compactness parameter, stability and adiabatic index has been provided. It is important to mention here that our obtained solutions are physically viable and are well stable.

gr-qc↗

arXiv2021

Traversable wormholes in the extended teleparallel theory of gravity with matter coupling

This study explores the Gaussian and the Lorentzian distributed spherically symmetric wormhole solutions in the $f(τ, T)$ gravity. The basic idea of the Gaussian and Lorentzian noncommutative geometries emerges as the physically acceptable and substantial notion in quantum physics. This idea of the noncommutative geometries with both the Gaussian and Lorentzian distributions becomes more striking when wormhole geometries in the modified theories of gravity are discussed. Here we consider a linear model within $f(τ,T)$ gravity to investigate traversable wormholes. In particular, we discuss the possible cases for the wormhole geometries using the Gaussian and the Lorentzian noncommutative distributions to obtain the exact shape function for them. By incorporating the particular values of the unknown parameters involved, we discuss different properties of the new wormhole geometries explored here. It is noted that the involved matter violates the weak energy condition for both the cases of the noncommutative geometries, whereas there is a possibility for a physically viable wormhole solution. By analyzing the equilibrium condition, it is found that the acquired solutions are stable. Furthermore, we provide the embedded diagrams for wormhole structures under Gaussian and Lorentzian noncommutative frameworks. Moreover, we present the critical analysis on an anisotropic pressure under the Gaussian and the Lorentzian distributions.

gr-qc↗

arXiv2021

Anisotropic spheres via embedding approach in $\mathcal{R}+β\mathcal{R}^{2}$ gravity with matter coupling

The manifesto of the current article is to investigate the compact anisotropic matter profiles in the context of one of the modified gravitational theories, known as $f(\mathcal{R}, \mathcal{T})$ gravity, where $\mathcal{R}$ is a Ricci Scalar and $\mathcal{T}$ is the trace of the energy-momentum tensor. To achieve the desired goal, we capitalized on the spherical symmetric space-time and utilized the embedding class-1 solution via Karmarkar's condition in modeling the matter profiles. To calculate the unidentified constraints, Schwarzschild exterior solution along with experimental statistics of three different stars LMC X-4, Cen X-3, and EXO 1785-248 are taken under consideration. For the evaluation of the dynamical equations, a unique model $f(\mathcal{R}, \mathcal{T})=\mathcal{R}+β\mathcal{R}^2+λ\mathcal{T}$ has been considered, with $β$ and $λ$ being the real constants. Different physical aspects have been exploited with the help of modified dynamical equations. Conclusively, all the stars under observations are realistic, stable, and are free from all singularities.

gr-qc↗

arXiv2020

Bardeen Stellar Structures with Karmarkar Condition

Current study is focussed to discuss the existence of a new family of compact star solutions by adopting the Karmarkar condition in the background of Bardeen black hole geometry. For this purpose, we consider static spherically symmetric spacetime with anisotropic fluid distribution in the presence of electric charge. We consider a specific model of $g_{rr}$ metric function, to describe a new family of solutions which satisfies the Karmarkar condition. Further, we investigate the interior solutions for two different models of compact stars with observational mass and radii, i.e., $(M=1.77M_{\odot}, \;R_{b}=9.56km)$ and $(M=1.97M_{\odot}, \;R_{b}=10.3km)$. It is found that these solutions fulfill all the necessary conditions for a charged star. Through graphical discussion, it is noticed that our calculated solutions are physically arguable with a best degree of accuracy for $n\in[1.8,7)$, where parameter $n$ is involved in the model under discussion. However, it is perceived that the presented model violates all the physical conditions for $n\in\{2,4,6\}$. Finally, it is concluded that the parameter $n$ has a strong impact on the obtained solutions in the context of Bardeen stellar structures.

gr-qc↗

arXiv2018

Stellar Hydrostatic Equilibrium Compact Structures in $f(\mathcal{G},T)$ Gravity

In this paper, stellar hydrostatic equilibrium configuration of the compact stars (neutron stars and strange stars) has been studied for $f(\mathcal{G},T)$ gravity model, with $\mathcal{G}$ and $T$ being the Gauss-Bonnet invariant and the trace of energy momentum tensor, respectively. After having derived the hydrostatic equilibrium equations for $f(\mathcal{G},T)$ gravity, the fluid pressure for the neutron stars and the strange stars has been computed by implying two equation of state models corresponding to two different existing compact stars. For the $f(\mathcal{G},T)=α{\mathcal{G}^n+λ{T}}$ gravity model, with $α$, $n$, and $λ$ being some specific constants, substantial change in the behavior of the physical attributes of the compact stars like the energy density, pressure, stellar mass, and total radius has been noted with the corresponding change in $λ$ values. Meanwhile, it has been shown that for some fixed central energy density and with increasing values of $λ$, the stellar mass both for the neutron stars and the strange stars increases, while the total stellar radius $R$ exhibits the opposite behavior for both of the compact stars. It is concluded that for this $f(\mathcal{G},T)$ stellar model, the maximum stellar mass can be boosted above the observational limits.

physics.gen-ph↗

arXiv2018

Gravastars in $f(\mathcal{G},T)$ Gravity

This work proposes a stellar model under Gauss-Bonnet $f(\mathcal{G}, T)$ gravity with the conjecture theorised by Mazur and Mottola, well known as the gravitational vacuum stars (gravastars). By taking into account the $f(\mathcal{G},T)$ stellar model, the structure of the gravastar with its exclusive division of three different regions namely, (i) the core interior region (ii) the junction region (shell), and (iii) the exterior region, has been investigated with reference to the existence of energy density, pressure, ultra-relativistic plasma, and repulsive forces. The different physical features like, the equation of the state parameter, length of the shell, entropy, energy-thickness relation of the gravastar shell model have been discussed. Also, some other physically valid aspects have been presented with the connection to non-singular and event-horizon free gravastar solutions, which in contrast to a black hole solution, might be stable without containing any information paradox.

gr-qc↗

arXiv2017

Emerging Anisotropic Compact Stars in $f(\mathcal{G},T)$ Gravity

The possible emergence of compact stars has been investigated in the recently introduced modified Gauss-Bonnet $f(\mathcal{G},T)$ gravity, where $\mathcal{G}$ is the Gauss-Bonnet term and ${T}$ is the trace of the energy-momentum tensor. Specifically, for this modified $f(\mathcal{G}, T)$ theory, the analytic solutions of Krori and Barua have been applied to anisotropic matter distribution. To determine the unknown constants appearing in Krori and Barua metric, the well-known three models of the compact stars namely 4U1820-30, Her X-I, and SAX J 1808.4-3658 have been used. The analysis of the physical behavior of the compact stars has been presented and the physical features like energy density and pressure, energy conditions, static equilibrium, stability, measure of anisotropy, and regularity of the compact stars, have been discussed.

gr-qc↗

arXiv2017

Effects of quantum statistical pressure and exchange correlation on the low frequency electromagnetic waves in degenerate Fermi-Dirac pair-ion plasma

The low frequency, long wavelength electromagnetic waves, viz, shear Alfven wave in quantum electron-positron-ion magneto plasmas, have been examined using quantum magneto hydrodynamic model. In this model, we have considered electrons and positrons are to be magnetized as well as degenerate whereas ions are magnetized but classical. We have also included the effects of exchange correlation terms which appear entirely the dynamic equations of electrons and positrons. The whole treatment is done using multi-fluid model. Our object is to study the shear Alfvén waves propagating in above said system of plasma. For that we have derived the modified dispersion relation of the shear Alfvén waves. Results are relevant to the terrestrial laboratory astrophysics.

physics.plasm-ph↗

arXiv2017

Some Exact Solutions in $f(\mathcal{G},T)$ Gravity via Noether Symmetries

This paper is devoted to investigate the recently proposed modified Gauss-Bonnet $f(\mathcal{G},T)$ gravity, with $\mathcal{G}$, the Gauss-Bonnet term, coupled with ${T}$, the trace of energy-momentum tensor. We have used the Noether symmetry methodology to discuss some cosmologically important $f(\mathcal{G},T)$ gravity models with anisotropic background. In particular, the Noether symmetry equations for modified $f(\mathcal{G},T)$ gravity are reported for locally rotationally symmetric Bianchi type $I$ universe. Explicitly, two models have been proposed to explore the exact solutions and the conserved quantities. It is concluded that the specific models of modified Gauss-Bonnet gravity may be used to reconstruct $Λ$CDM cosmology without involving any cosmological constant.

gr-qc↗

arXiv2017

Noether Symmetry Approach in $f(\mathcal{G},T)$ Gravity

We explore the recently introduced modified Gauss-Bonnet gravity [1], $f(\mathcal{G},T)$ pragmatic with $\mathcal{G}$, the Gauss-Bonnet term, and ${T}$, the trace of the energy-momentum tensor. Noether symmetry approach has been used to develop some cosmologically viable $f(\mathcal{G},T)$ gravity models. The Noether equations of modified gravity are reported for flat FRW universe. Two specific models have been studied to determine the conserved quantities and exact solutions. In particular, the well known deSitter solution is reconstructed for some specific choice of $f(\mathcal{G},T)$ gravity model.

physics.gen-ph↗