arXiv subjects

Byon N. Jayawiguna

Publications and source records attributed to Byon N. Jayawiguna.

6 recordsLinked to original sources

arXiv2026

New Universal Relations for Magnetized Neutron Stars

Unlike the neutron-star mass--radius relation, which depends sensitively on the internal stellar structure through the equation of state of dense nuclear matter, certain neutron-star properties obey approximately universal relations that exhibit only weak dependence on the equation of state. In this paper, we explore new universal relations for magnetized neutron stars. We focus on a purely poloidal dipolar magnetic-field configuration and treat the effects of the magnetic field perturbatively to second order in the field strength. After appropriately normalizing the relevant quantities by the stellar mass and the magnetic-field strength at the pole, we first identify an exact universal relation between the magnetic dipole moment and stellar compactness. We then find approximate universal relations among the magnetic dipole moment, magnetically-induced stellar quadrupole moment, and ellipticity, with fractional variations due to the equation of state at the level of O(10%). We support these numerical findings with analytic estimates for Newtonian polytropes, which reproduce the observed behavior. Among the newly discovered relations, the one connecting the magnetic dipole moment and stellar quadrupole moment may be particularly useful for the analysis of gravitational-wave signals from binaries containing magnetized neutron stars.

gr-qc↗

arXiv2025

Slowly Rotating and Tidal Deformation of Nonlocal Modified Tolman VII Star

We investigate the moment of inertia, quadrupole deformation, and tidal deformation within the framework of nonlocal gravity, utilizing the exact modified Tolman-VII (NEMTVII) density model with an isotropic perfect fluid. The Love number~$(k_{2})$ is derived using standard even-parity perturbation theory. Additionally, we explore the observational implications by analyzing the tidal deformability parameter~$( λ_{\textrm{tid}} )$ in comparison with the constraints from GW170817, GW190425, PSR J0348+0432, and PSR J0740+6620. We found that the results are consistent with the tidal constraint when $α\gtrsim 1.6$ with the small $β$. For slowly rotating object, the dimensionless moment of inertia~$( \bar{I} )$, rotational Love parameter~$( \barλ_{\textrm{rot}} )$, and quadrupole moment~$( \bar{Q} )$ are fully determined by the perturbed metric. Our findings reveal that the nonlocal parameter~$( β)$ significantly affects the star radius. For a fixed $β$ and varying $α$, the $I$-Love-$Q$ relations are found to be universal. For varying $β$, the $I$-Love-$Q$ relations become non-universal.

gr-qc↗

arXiv2023

Gravitational Perturbation in Nonlocal Modified Tolman VII Model

In comparison to the original Tolman VII model, Exact Modified Tolman VII (EMTVII) with one additional parameter can increase the compactness of compact object. When the compactness is in the ultracompact regime, the quasinormal modes~(QNMs) of the trapped mode as well as the gravitational echoes become more viable. Starting with the EMTVII model, we introduce nonlocality into the matter sector and analyze the effective potential, the QNMs, and the gravitational echoes of the compact and ultracompact object in the nonlocal model. The nonlocal gravity version of EMTVII~(NEMTVII) is parametrized by the nonlocal parameter~($ β$), modified Tolman VII parameter ($ α$), and the compactness ($ \mathcal{C}$). It is found that the nonlocal profile produces the smeared surface and consequently reduce the compactness. The maximum compactness $\mathcal{C}_{max}=0.4$ occurs when $α=0=β$, i.e., EMTVII with no smearing. For relatively small value of $β= 0.01$ and the compactness $ \mathcal{C} \lesssim 0.2667$~(with $M=2.14$ solar masses, $R=11.835$ km at $α=1.4$), the causality condition and the dominant energy condition~(DEC) are satisfied. The quasinormal modes of the gravitational perturbation are calculated using Bohr-Sommerfeld (BS) fitting and we find that the nonlocality produces less trapped modes than the original (EMTVII) counterpart. At high compactness, gravitational echoes are simulated numerically. Echoes are found to exist in the parameter space where the dominant energy condition and the causality condition are violated.

gr-qc↗

arXiv2020

A Nonsingular Kerr-Sen Black Hole

We present a novel solution describing four dimensional rotating regular charged black hole in the low energy heterotic string theory. This present solution is characterized by its mass, charged, as well as angular momentum. Some aspect including event horizon, ergosphere, and the angular velocity are discussed. It is shown that later, our expression for event horizon and ergosphere cannot be obtained analytically. On the other hand, to ensure whether our solution describe a nonsingular rotating charged black hole, we use two type of scalar invariant; contracted Ricci tensor and Kretschmann scalar. From our result, the inclusion of charge does not alter the regularity of a black hole. We also proposed a natural prescription to have rotating charged black hole solution with a minimal violation of weak energy conditions.

gr-qc↗

arXiv2020

Three Dimensional Black Hole in the Low Energy Heterotic String Theory

We study the BTZ black holes (2+1 dimensional space-time) in the low energy heterotic string theory (BTZ-Sen BH). This concept requires us to include a non-trivial dilaton $ ϕ$ and a 3-form $ H_{μνρ} $ field. By using the Hassan-Sen transformation and BTZ black hole as a seed solution, we obtain the solution in the string frame. Some properties of the black hole solutions are discussed.

gr-qc↗

arXiv2019

Charged black holes in higher-dimensional Eddington-inspired Born-Infeld gravity

We study static (electrically)-charged solutions of Eddington-inspired Born-Infeld (EiBI) theory of gravity in general $D$-dimensional spacetime. We consider both linear (Maxwell) as well as nonlinear electrodynamics for the matter fields. In this particular work, the nonlinear theory we specifically consider is the Born-Infeld electrodynamics. The solutions describe higher-dimensional black holes in EiBI gravity. For the linear Maxwell field, we show that the electric field is still singular for $D>4$. This singularity is cured when EiBI is coupled to the BI electrodynamics. We obtain EiBI-BI black hole solutions in the limit of ${\tildeα}\equiv4κb^2/λ=1$ and $2$. We also investigate their thermodynamical property. It is found that $κ$ imposes a charge screening that makes the corresponding Hawking temperature experiences some sudden jump from charged-type to the Schwarzschild-type at some critical value of $κ$. Thermodynamical stability reveals that the EiBI-BI black holes can exist with smaller horizon than the RN.

gr-qc↗