arXiv subjects

Zainab Malik

Publications and source records attributed to Zainab Malik.

15 recordsLinked to original sources

arXiv2026

Long-lived massive scalar modes, grey-body factors, and absorption cross sections of the Reissner--Nordstr\"om-like brane-world black hole

We study quasinormal modes, including the quasi-resonant regime, grey-body factors, and absorption cross sections of a massive scalar field in a Reissner--Nordstr\"om-like brane-world black hole endowed with a tidal-charge parameter induced by extra-dimensional effects. Combining semiclassical WKB calculations with time-domain evolution, we determine the range of parameters for which the effective potential keeps the single-barrier shape needed for a reliable quasinormal-mode and scattering analysis. We find that increasing positive tidal charge lowers the barrier, drives the spectrum closer to the quasi-resonant regime, and enhances transmission and absorption, whereas increasing the field mass or multipole number makes the barrier less transparent and shifts absorption to higher frequencies. Our results indicate the onset of an arbitrarily long-lived quasinormal-mode regime. At the same time, this behavior cannot be followed directly in the time-domain profiles, because the asymptotic tails set in too early and mask the late-time ringing.

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arXiv2026

Analytic Quasinormal Spectrum of Effective de Sitter Space in Generalized Proca Theory

Quasinormal modes describe the relaxation of perturbed black holes and relate ringdown observables to the background geometry. In this work we study the problem in a de Sitter setting within a generalized Proca branch that generates an effective positive cosmological constant and admits an exact de Sitter vacuum. Using this vacuum, we derive closed expressions for scalar mode frequencies and identify the change in damping behavior between light and heavy fields. The resulting formulas show explicitly how the theory parameters determine the de Sitter-like part of the spectrum.

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arXiv2026

Thermodynamic, Optical, and Orbital Signatures of Regular Asymptotically Flat Black Holes in Quasi-Topological Gravity

This study provides an analytic and numerical characterization of a class of regular, asymptotically flat black holes described by a deformed static spherical metric. The model is grounded in a four-dimensional non-polynomial quasi-topological framework in which higher-curvature corrections remain dynamically nontrivial while the static spherical sector retains a reduced-order structure, enabling tractable black-hole solutions with regular cores. Starting from the existence conditions of horizons and regularity, the allowed parameter domain and the extremal bound are derived. Hawking temperature, shadow radius, photon-ring Lyapunov exponent, and ISCO binding efficiency are then analyzed across the physically allowed parameter space. We further extend the analysis to Novikov--Thorne thin-disk accretion by deriving the flux kernel, effective-temperature profile, and bolometric luminosity scaling, and by providing representative numerical datasets for these quantities. A coherent trend emerges: increasing the deformation parameter drives the solution away from Schwarzschild behavior, reducing temperature, shadow size, and photon-orbit instability rate while enhancing orbital binding efficiency and accretion luminosity; increasing the exponent $ν$ suppresses deformation effects and restores Schwarzschild-like observables. These results provide a compact phenomenological map linking horizon structure, thermodynamics, optical signatures, dynamical instability, and thin-disk accretion diagnostics in this regular black-hole family.

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arXiv2026

Analytic Expressions for Quasinormal Modes of a Regular Black Hole Sourced by a Dehnen-Type Halo

Using an expansion beyond the eikonal regime, we derive relatively compact and accurate analytic expressions for the gravitational quasinormal modes of an asymptotically flat black hole supported by a Dehnen-type dark-matter halo. The spacetime admits a simple analytic metric describing a supermassive black hole embedded in a galactic environment, with the lapse function $f(r)=1-\frac{2 M r^{2}}{(r+a)^{3}}.$ The parameter $a$ sets the characteristic scale of the surrounding halo and controls the regularization of the central region. The axial gravitational sector splits into two distinct channels, referred to as the "up" and "down" perturbations, which are not isospectral.

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arXiv2025

Long-lived quasinormal modes and grey-body factors of supermassive black holes with a dark matter halo

We study quasinormal modes and grey-body factors of a massive scalar field in the background of a Schwarzschild black hole surrounded by a spherically symmetric galactic dark matter halo. The background metric, recently obtained as an analytic generalization of the Schwarzschild geometry, depends on the halo velocity parameter $V_{c}$ and the core radius $a$. Using the sixth- and seventh-order WKB methods with Pade approximants, supported by time-domain integration and Prony analysis, we compute the fundamental quasinormal frequencies and transmission coefficients. The results show that the real part of the frequency slightly increases while the damping rate decreases with growing field mass $\mu$, leading to longer-lived oscillations. The influence of the dark matter halo parameters is found to be negligible for astrophysically realistic values, confirming the robustness of Schwarzschild-like ringdown signatures. Grey-body factors decrease with increasing field mass and multipole number, while the effect of the halo parameters remains small.

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arXiv2025

Gravitational perturbations of the Hayward spacetime and testing the correspondence between quasinormal modes and grey-body factors

The paper studies axial gravitational perturbations of the Hayward black hole, a regular geometry that also arises as an effective solution in asymptotically safe gravity. By computing grey-body factors with the 6th-order WKB method and comparing them to predictions based on the quasinormal modes, the correspondence between transmission coefficients and quasinormal spectra is verified. Quantum corrections, parametrized by $γ$, are shown to suppress both the grey-body factors and the absorption cross-section, while the correspondence remains accurate at the percent level for low multipoles and essentially exact for higher ones.

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arXiv2025

Bonanno-Reuter regular black hole: quasi-resonances, grey-body factors and absorption cross-sections of a massive scalar field

We study quasinormal modes of a massive scalar field in the background of the regular, quantum-corrected Bonanno-Reuter black hole, which arises from the renormalization group improvement of the Schwarzschild solution within the framework of asymptotically safe gravity. The analysis is performed in both the time and frequency domains. We find that increasing the mass of the field leads to a strong suppression of the damping rate, and extrapolation to larger masses indicates the emergence of arbitrarily long-lived oscillations, or quasi-resonances. In the time domain, the late-time decay follows an asymptotic behavior that differs from the power-law tails of the classical Schwarzschild case. Furthermore, we compute the grey-body factors and absorption cross-sections for the massive scalar field and show that the grey-body factors decrease as the field mass increases, effectively shifting the emitted radiation spectrum toward higher frequencies.

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arXiv2025

Grey-Body Factors for Scalar and Dirac Fields in the Euler-Heisenberg Electrodynamics

We study grey-body factors of neutral scalar and Dirac fields in the background of charged black holes arising in the Einstein--Euler--Heisenberg (EEH) theory. The Euler--Heisenberg corrections, which represent nonlinear electrodynamical effects due to vacuum polarization, modify the effective potential barrier surrounding the black hole and thereby affect the transmission probabilities for Hawking quanta. Using the sixth-order WKB method, and verifying our results against the recently proposed correspondence between grey-body factors and quasinormal modes, we compute the frequency-dependent grey-body spectra for various values of the black hole charge and EEH coupling. We find that the nonlinear coupling systematically lowers the effective potential barrier, enhancing the transmission probability. This work represents the first step toward incorporating nonlinear QED effects into the study of Hawking evaporation, focusing here on neutral test fields.

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arXiv2025

Long-Lived Quasinormal Modes of Brane-Localized Reissner-Nordström--de Sitter Black Holes

We study the quasinormal modes of a massive scalar field propagating on the Reissner-Nordström--de Sitter (RNdS) black hole black hole background on a 3+1-dimensional brane embedded in a higher-dimensional world. Using the WKB method supplemented with Padé approximants and validated by time-domain integration via the Prony method, we compute the dominant quasinormal frequencies for a wide range of black hole and field parameters. We show that the presence of the cosmological constant, black hole charge, and bulk dimensionality significantly affect the oscillation frequencies and damping rates of the scalar perturbations. In particular, we observe the emergence of long lived modes and slowly decaying oscillatory tails in the regime of large field mass. The results demonstrate good agreement between the frequency- and time-domain methods, reinforcing the reliability of the semi-analytic approach in this context.

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arXiv2025

Perturbations and Quasinormal Modes of the Dirac Field in Effective Quantum Gravity

Recently, two models of quantum-corrected Schwarzschild-like black holes were developed within Effective Quantum Gravity, and the spectra of bosonic perturbations have been analyzed in several recent studies. In this work, we investigate the quasinormal modes of a massless Dirac field perturbations around these black holes. By employing the higher-order WKB method and time-domain integration, we achieved consistency between the two approaches within their common range of validity. This concordance enables us to distinguish the two quantum-corrected black hole models from each other and from their Schwarzschild limit through their quasinormal spectra. In addition, we find approximate analytic expressions for quasinormal modes and grey-body factors in the form of expansion beyond the eikonal limit.

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arXiv2024

Correspondence between quasinormal modes and grey-body factors for massive fields in Schwarzschild-de Sitter spacetime

Recently, a correspondence between quasinormal modes and grey-body factors of black holes has been established. This correspondence is known to be exact in the eikonal regime for a large class of asymptotically flat black holes and approximate when the multipole number $ \ell $ is small. In this work, we demonstrate that there exists a regime where the correspondence holds with unprecedented accuracy even for the lowest multipole numbers: specifically, for perturbations of massive fields in the background of asymptotically de Sitter black holes, provided the field mass is not very small. We also fill the gap in the existing literature via finding the grey-body factors of a massive scalar field in the Schwarzschild- de Sitter background, when $μM/m_{P}$ is not small.

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arXiv2024

Quasinormal modes and grey-body factors of Morris-Thorne wormholes

Using the fact that, for a broad class of Morris-Thorne wormholes, the maximum of the effective potential is located at the throat, we derive accurate analytic WKB expressions for the quasinormal modes and grey-body factors of various traversable wormholes. In the eikonal limit, these analytic expressions acquire a compact form and satisfy the correspondence between the quasinormal modes and the radii of the wormhole shadows.

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arXiv2024

Analytical QNMs of fields of various spin in the Hayward spacetime

By employing an expansion in terms of the inverse multipole number, we derive analytic expressions for the quasinormal modes (QNMs) of scalar, Dirac, and Maxwell perturbations in the Hayward black hole (BH) background. The metric has three interpretations: as a model for a radiating BH, as a quantum-corrected BH owing to the running gravitational coupling in the Asymptotically Safe Gravity, and as a BH solution in the Effective Field Theory. We show that the obtained compact analytical formulas approximate QNMs with remarkable accuracy for $\ell > 0$.

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arXiv2024

Quasinormal Modes of Dilaton Black Holes: Analytic approximations

We have derived precise analytic expressions for the quasinormal modes of test scalar, and Dirac fields in the background of the dilaton black hole. To achieve this, we employ the higher-order WKB expansion in terms of $1/\ell$. A comparison between the analytic formulas and time-domain integration reveals that the analytic approach generally yields more accurate results than the numerical results previously published using the lower-order WKB approach. We demonstrate that in the eikonal regime, test fields adhere to the correspondence between null geodesics and eikonal quasinormal modes.

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arXiv2024

Quasinormal modes of the bumblebee black holes with a global monopole

We compute quasinormal modes of test fields around spherically symmetric black holes with a global monopole in bumblebee gravity. The frequency of oscillation and the damping rate exhibit significant decreasing as the global monopole parameter is increased. An intriguing observation arises in the extreme limit, where the quasinormal modes manifest a form of universal behavior: the actual oscillation frequency remains unaltered despite variations in the Lorentz symmetry breaking (LSB) parameter. Our calculations are conducted through two distinct methods, both of which yield results that align remarkably well. Furthermore, we derive an analytical formula for quasinormal modes within the eikonal approximation and beyond it. In the limits of either vanishing deficit angle or bumblebee parameters, the compact and sufficiently accurate analytic expressions for quasinormal modes are obtained.

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