arXiv subjects

K. N. Singh

Publications and source records attributed to K. N. Singh.

4 recordsLinked to original sources

arXiv2026

Holographic dark energy as a source for slowly rotating wormholes: Implications for null geodesics and shadows

In this work, we explore for the first time slowly rotating traversable wormholes embedded in holographic dark energy. We focus on three representative holographic dark energy models -- Rényi, mixed, and Moradpour -- and construct the wormhole shape functions directly from these energy density profiles using a Teo-type rotating wormhole metric. This allows us to examine the wormhole geometry in detail, including throat structure, the flaring-out condition for safe traversal, and violations of the null energy condition. To capture the effects of different redshift behaviors, we consider three smooth hyperbolic redshift functions -- Sinh, Cosh, and Tanh -- and study how they influence photon motion, null geodesics, effective potentials, photon-sphere locations, and Lense-Thirring precession caused by wormhole rotation. Our analysis shows that cuspy Rényi profiles produce tighter photon orbits and stronger asymmetry, while smoother mixed and Moradpour profiles allow more circular paths and weaker frame-dragging effects. Finally, we calculate the shadows cast by these wormholes, finding that Rényi-supported wormholes generate smaller, asymmetric shadows, whereas mixed and Moradpour-supported wormholes produce larger, nearly circular silhouettes. Altogether, this study provides a detailed theoretical picture of photon dynamics, shadow morphology, and relativistic effects in slowly rotating wormholes within realistic holographic dark energy environments, offering potential guidance for observational signatures of these exotic objects.

gr-qc↗

arXiv2026

Probing geometrically perturbed strange stars with minimal decoupling using millisecond pulsar timing observations

We construct a gravitationally decoupled anisotropic strange star model using the minimal geometric deformation approach with a MIT bag equation of state and an additional source sector controlled by a deformation parameter $β$ and a radial perturbation scale $Ψ$ through $g(r)=\sin(Ψr^{2})$. The resulting Einstein system is consistently split into seed and $θ$-sectors and matched to an exterior Schwarzschild geometry. The model is constrained by high-mass pulsars: PSR J0740+6620 $(2.08\pm0.07\,M_\odot)$, PSR J1810+1744 $(2.13\pm0.04\,M_\odot)$, PSR J1959+2048 $(2.18\pm0.09\,M_\odot)$, and PSR J2215+5135 $(2.28^{+0.10}_{-0.09}\,M_\odot)$. It reproduces these objects with predicted radii $R \approx 11.3$--$12.9$ km. The maximum mass reaches $M_{\max} \approx 2.28\,M_\odot$ for $β= 3\times 10^{-3}$ and $Ψ\approx 0.03\,\text{km}^{-2}$, while for $β= 10^{-3}$ the configuration yields $M_{\max} \approx 2.12\,M_\odot$ with $R \approx 12.2$ km. The central density lies in $ρ_c \approx (2.4$--$3.1)\times 10^{-4}\,\text{km}^{-2}$, decreasing smoothly to $ρ_s \approx 2.0\times 10^{-4}\,\text{km}^{-2}$. The anisotropy increases from zero at the center to $Δ\approx (0.25$--$0.45)\times 10^{-4}\,\text{km}^{-2}$ near the surface, generating additional outward support that enhances compactness by $\sim 15\%$. The compactness parameter spans $C \approx 0.17$--$0.22$, safely below the Buchdahl limit, while the surface redshift reaches $z_s \approx 0.25$--$0.38$. The condition $dM/dρ_c > 0$ is satisfied throughout, confirming dynamical stability. Overall, $β$ enhances the maximum mass by up to $\sim 15\%$, while $Ψ$ introduces controlled oscillatory structure without violating observational constraints, producing stable ultra-compact stars consistent with current pulsar data.

gr-qc↗

arXiv2023

The effect of gravitational decoupling on constraining the mass and radius for the secondary component of GW190814 and other self-bound strange stars in f(Q)-gravity theory

Inspired by the conundrum of the gravitational event, GW190814 which brings to light the coalescence of a 23 $ M_{\odot}$ black hole with a yet to be determined secondary component, we look to modelling compact objects within the framework of $f(\mathcal{Q})$ gravity by employing the method of gravitational decoupling. We impose a quadratic equation of state (EOS) for the interior matter distribution which in the appropriate limit reduces to the MIT bag model. The governing field equations arising from gravitational decoupling bifurcates into the $ρ=θ^0_0$ and $p_r=θ^1_1$ sectors leading to two distinct classes of solutions. Both families of solutions are subjected to rigorous tests qualifying them to describe a plethora of compact objects including neutron stars, strange stars and the possible progenitor of the secondary component of GW190814. Using observational data of mass-radius relations for compact objects LMC X-4, Cen X-3, PSR J1614-2230 and PSR J0740+6620 we show that it is possible to generate stellar masses and radii beyond 2.0 $ M_{\odot}$ for neutron stars. Our findings reveal that the most { suitable and versatile model in this framework is the quadratic EOS}, which accounts for a range of low mass stars as well as typical stellar candidates describing the secondary component of GW190814.

gr-qc↗

arXiv2019

A generalized Finch-Skea class one static solution

In the present article, we discuss relativistic anisotropic solutions of the Einstein field equation for the spherically symmetric line element under the class I condition. To do so we apply the embedding class one technique using Eisland condition. Within this approach, one arrives at a particular differential equation that links the two metric components $e^ν$ and $e^λ$. In order to obtain the full space-time description inside the stellar configuration we ansatz the generalized form of metric component $g_{rr}$ corresponding to the Finch-Skea solution. Once the space-time geometry is specified we obtain the complete thermodynamic description i.e. the matter density $ρ$, the radial, and tangential pressures $p_r$ and $p_t$, respectively. Graphical analysis shows that the obtained model respects the physical and mathematical requirements that all ultra-high dense collapsed structures must obey. The $M-R$ diagram suggests that the solution yields stiffer EoS as parameter $n$ increases. The $M-I$ graph is in agreement with the concepts of Bejgar et al. \cite{bej} that the mass at $I_{max}$ is lesser by few percent (for this solution $\sim 3\%$) from $M_{max}$. This suggests that the EoSs is without any strong high-density softening due to hyperonization or phase transition to an exotic state.

physics.gen-ph↗