arXiv subjects

Alexey Dubinsky

Publications and source records attributed to Alexey Dubinsky.

16 recordsLinked to original sources

arXiv2026

Wave and particle probes of a regular T-duality-inspired black hole with gravitational self-energy

Recently it was shown that a non-local T-duality-inspired smearing of the point mass introduces a finite zero-point length, while the regularized Newtonian gravitational self-energy is promoted to an additional source for the spacetime. The result is a nonsingular black-hole geometry whose ADM mass contains a finite self-energy contribution and whose extremal Planck-scale remnant sector has been proposed as a possible dark-matter component. We study how this spacetime would affect two familiar physical signals: the ringing of a massive scalar field and the motion of particles and light near the horizon. The zero-point length smooths the central region and changes the strong-field potential outside the horizon. On the wave side, we find that making the scalar field heavier increases the oscillation frequency and makes the damping weaker, a behavior associated with long-lived ringing. On the particle side, increasing the zero-point length makes the photon orbit and the innermost stable circular orbit more compact in physical mass units. The corresponding shadow becomes smaller, the photon-ring frequency becomes larger, and the orbital binding energy increases. These results show that the same regularizing correction leaves related imprints in wave propagation, black-hole shadows and circular-orbit physics.

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arXiv2026

From Ringdown to Lensing: Analytic Eikonal Modes of Quasi-Topological Regular Black Holes

We develop an analytic eikonal description of perturbations for four-dimensional regular black holes in quasi-topological gravity. Using first-order Schutz--Will WKB together with a small-coupling expansion and a large-$\ell$ expansion, we obtain closed quasinormal-mode formulas with explicit dependence on the black-hole parameters $(M,\mu,\nu,\alpha)$. We then map the same geodesic invariants $(\Omega_{\text{ph}},\lambda_{\text{ph}})$ to shadow and strong-lensing observables, deriving an explicit QNM--shadow--lensing correspondence. In this way, ringdown frequencies, shadow scale, and strong-deflection observables are unified in one analytic scheme for this quasi-topological family.

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arXiv2026

Scattering of a scalar field in the four-dimensional quasi-topological gravity

We study grey-body factors for a massless scalar field in the spacetime of regular black holes arising in four-dimensional non-polynomial quasi-topological gravity. We consider two representative metrics that capture the typical features of regular geometries. Using the WKB method, we compute the transmission probabilities and analyze their dependence on the regularization parameter. The grey-body factors are found to deviate only slightly from the Schwarzschild case, indicating that the scattering properties are largely insensitive to near-horizon regularization of the geometry. The correspondence between quasinormal modes and grey-body factors is shown to be sufficiently accurate for higher multipole numbers.

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arXiv2025

Long-lived modes and grey-body factors of massive fields in quantum-corrected (Hayward) black holes

We study the dynamics of a massive scalar field in the background of the Hayward black hole, which can be interpreted both as a regular spacetime and as an effective geometry arising from Asymptotically Safe gravity. The quasinormal spectrum and grey-body factors are computed using the WKB method with Pad\'e improvements and confirmed through time-domain integration followed by Prony analysis. We find that the mass of the field significantly suppresses the damping rate of quasinormal oscillations, giving rise to long-lived modes that continuously approach arbitrarily long-lived states (quasi-resonances) at certain critical field masses. In the time domain, the standard exponentially decaying ringdown is replaced by oscillatory tails with a power-law envelope. The corresponding grey-body factors reveal a pronounced shift of the transmission peak toward higher frequencies and a suppression of the low-frequency part of the spectrum. Finally, we show that the correspondence between quasinormal modes and grey-body factors remains valid for massive fields, being highly accurate for large multipole numbers and gradually losing precision as either the field mass increases or the multipole number decreases.

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arXiv2025

Scattering and Absorption of Standard Model Fields by Brane-Localized Schwarzschild--de Sitter Black Holes

We investigate the propagation and absorption of Standard Model fields -- scalar, electromagnetic, and Dirac -- on a 3+1-dimensional brane embedded in a higher-dimensional Schwarzschild--de Sitter (SdS) spacetime. Using the effective four-dimensional projection of the Tangherlini metric, we compute grey-body factors (GBFs) and absorption cross-sections for each spin sector by means of the sixth-order WKB method and, independently, via the recently proposed correspondence between quasinormal modes (QNMs) and transmission coefficients. The results demonstrate that the cosmological constant and field mass crucially affect the transmission probabilities: increasing $\Lambda$ lowers the potential barrier and enhances the transparency of the geometry, while a larger field mass $\mu$ suppresses low-frequency emission and shifts the absorption spectrum to higher energies. For all fields, the QNM--GBF correspondence proves reliable to within about one percent for multipoles $\ell \ge 2$, while the correspondence remains less accurate for the lowest multipoles. The total absorption cross-sections exhibit the expected transition from the low-frequency suppression to the geometric-optics regime. Overall, these findings provide quantitative insight into the interplay between dimensionality, cosmological expansion, and black-hole radiation on the brane.

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arXiv2025

Gravitational perturbations of Dymnikova black holes: grey-body factors and absorption cross-sections

We study axial gravitational perturbations of the Dymnikova regular black hole, an asymptotically flat spacetime in which the Schwarzschild singularity is replaced by a de Sitter core. Using the WKB method with Pad\'e approximants, we compute grey-body factors, and absorption cross-sections, and test the recently proposed correspondence between quasinormal frequencies and transmission coefficients. We find that variations of the quantum parameter $l_{\rm cr}$ affect the effective potential only near the horizon, leading to minor deviations of grey-body factors and absorption cross-sections from the Schwarzschild case. As a result, the Hawking radiation spectrum is governed mainly by the modified Hawking temperature, with grey-body factors providing only subleading corrections. Unlike higher quasinormal overtones, which are highly sensitive to near-horizon deformations, the grey-body factors remain robust, a feature explicitly confirmed for the Dymnikova geometry. The correspondence between quasinormal modes and grey-body factors holds in our case with high accuracy for multipoles $\ell \geq 2$.

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arXiv2025

Black Holes Immersed in Galactic Dark Matter Halo

We analyze the quasinormal modes (QNMs) of scalar, electromagnetic, and Dirac test fields in the background of a black hole immersed in a galactic dark matter halo. The analytic black hole solution considered here is sourced by a physically motivated halo density profile that leads to a flat galactic rotation curve. Using the sixth-order WKB method with Pad\'e approximants, we compute the QNM spectra for various field spins and parameter values, and provide numerical data in tabulated form. In addition to the numerical analysis, we derive analytic expressions for the quasinormal frequencies in the eikonal limit and beyond, by means of an expansion in inverse powers of the multipole number. We also calculate the Unruh temperature perceived by a static observer in the halo-modified spacetime. Our results demonstrate that the presence of the dark matter halo leads to observable modifications in the QNM spectra only if the density or compactness of the galactic halo is extraordinary high, so that quasinormal ringing a reliable observable for testing the black hole geometry, even in the presence of galactic environments.

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arXiv2025

Long-Lived Quasinormal Modes and Quasi-Resonances around Non-Minimal Einstein-Yang-Mills Black Holes

Using accurate computational methods, we compute the quasinormal frequencies of a massive scalar field propagating near a black hole in the framework of non-minimal Einstein-Yang-Mills theory with a non-zero cosmological constant. We show that increasing the mass of the scalar field significantly decreases the damping rate of the quasinormal modes for both asymptotically flat and de Sitter black holes. However, in the de Sitter case, arbitrarily long-lived modes can exist, whereas in the asymptotically flat case, the damping rate never vanishes completely. In the limit of quasi-resonances, we observe a kind of universal behavior where the frequencies do not depend on the coupling constant. Applying the time-domain integration of perturbation equations we show that even when the effective potential has a negative gap, the scalar field is stable and the perturbations decay in time. In the regime of large mass of the field we obtain the analytic formula for quasinormal modes.

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arXiv2024

Grey-body factors for gravitational and electromagnetic perturbations around Gibbons-Maeda-Garfinkle-Horovits-Strominger black holes

While grey-body factors for a test scalar field in stringy black holes described by the renowned Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS) solution have been analyzed in the literature, no such analysis exists for gravitons, likely due to the complexity of the perturbation equations. In this study, we utilize known data on quasinormal modes and the relationship between quasinormal modes and grey-body factors to derive these factors for gravitational and electromagnetic perturbations of the dilaton black hole. Our findings indicate that grey-body factors are significantly suppressed by the dilaton parameter as the black hole's charge approaches its extreme value. The iso-spectrality between axial and polar channels of perturbations is broken in the presence of the dilaton field, which leads to different grey-body factors for different types of perturbations.

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arXiv2024

Analytic expressions for grey-body factors of the general parametrized spherically symmetric black holes

In light of the recently discovered connection between grey-body factors and quasinormal ringing, we derive analytic expressions for the grey-body factors of generic parametrized spherically symmetric and asymptotically flat black holes. These expressions are presented as expansions in terms of the inverse multipole number and the coefficients of the parametrization. The obtained analytic formulas serve as good approximations whenever the deviation from the Schwarzschild geometry is not very large. We demonstrate that the primary parameter determining the grey-body factors is the deviation of the event horizon radius from its Schwarzschild value, while the higher-order coefficients of the parametrization, which govern the near-horizon geometry, are much less significant. This finding is consistent with recent observations that grey-body factors are considerably more stable against small deformations of the near-horizon geometry than quasinormal modes.

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arXiv2024

Analytic expressions for quasinormal modes of the general parametrized spherically symmetric black holes and the Hod's proposal

Using an expansion in terms of the inverse multipole number and the WKB approach, we derive an analytic expression for generic parametrized spherically symmetric and asymptotically flat black holes described by the Rezzolla-Zhidenko spacetime, in the regime when deviations from the Schwarzschild geometry are relatively small, i.e., when the coefficients of the parametrization are small. As an application of this analytic formula, we demonstrate that such generic black holes satisfy Hod's proposal, which constrains the damping rate of the least damped mode in relation to the Hawking temperature.

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arXiv2024

Quantum gravitational corrections to the Schwarzschild spacetime and quasinormal frequencies

Quantum gravitational corrections to the entropy of the Schwarzschild black hole, derived using the Wald entropy formula within an effective field theory framework, were presented in [X. Calmet, F. Kuipers Phys.Rev.D 104 (2021) 6, 066012]. These corrections result in a Schwarzschild spacetime that is deformed by the quantum correction. However, it is observed that the proposed quantum-corrected metric describes not a black hole, but a wormhole. Nevertheless, further expansion of the metric function in terms of the quantum correction parameter yields a well-defined black hole metric whose geometry closely resembles that of a wormhole. We also explore methods for distinguishing between these quantum-corrected spacetimes based on the quasinormal frequencies they emit. We show that while the fundamental mode deviates from the Schwarzschild limit only mildly, the first few overtones deviate at a strongly increasing rate, creating a characteristic ``sound'' of the event horizon.

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arXiv2024

Quasinormal modes of charged black holes in Asymptotically Safe Gravity

We calculate quasinormal modes of scalar and neutrino perturbations around the charged black hole in Asymptotically Safe Gravity. We show that the charge and coupling constant change the quasinormal spectrum considerably. We show that previous calculations of scalar quasinormal modes in this background [F. Javed, Phys. Dark Univ., 44, 101450 (2024)] suffer from a large numerical error exceeding the effect, that is, the deviations of the frequencies from their Schwarzschild limits. In the high frequency (eikonal) limit an explicit analytic formula for quasinormal modes is derived, which confirms the correspondence between the null circular geodesics and eikonal quasinormal frequencies.

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arXiv2024

Overtones of black holes via time-domain integration

We show that first several overtones could calculated by the time-domain integration method for asymptotically de Sitter black holes already at the lowest multipole numbers of gravitational and electromagnetic perturbations. This is not possible for asymptotically flat black holes, for which extraction of frequencies with the Prony method is usually possible with reasonable accuracy only for the fundamental mode. The reason for much better efficiency in the de Sitter case is absence of power-law tails: the quasinormal modes dominate the signal not only at the intermediate stage, but also at asymptotically late times.

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arXiv2024

Asymptotic decay and quasinormal frequencies of scalar and Dirac fields around dilaton-de Sitter black holes

We study the decay of Dirac and massive scalar fields at asymptotically late times in the background of the charged asymptotically de Sitter dilatonic black holes. It is shown that the asymptotic decay is exponential and oscillatory for large and intermediate mass of the field, while for zero and small mass it is pure exponential without oscillations. This reflects the dominance of quasinormal modes of the empty de Sitter spacetime at asymptotically late times. We also show that the earlier WKB calculation of the massive scalar field spectrum does not allow one to find the fundamental mode with reasonable accuracy.

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arXiv2024

Telling late-time tails for a massive scalar field in the background of brane-localized black holes

We examine perturbations of a massive scalar field around spherically symmetric, brane-localized black holes. Although the ringdown and asymptotic tails of various brane-world black holes have been extensively studied, there has been no analysis of the massive late-time tails for the simplest Schwarzschild-like, brane-localized black hole to date. We demonstrate that after the ringdown phase, two stages of oscillatory tails emerge - intermediate and asymptotic. The asymptotic decay law is distinct from those associated with Schwarzschild or Reissner-Nordstrom solutions.

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