Searcharxiv⌕ Search

arXiv subjects

S. V. Bolokhov

Publications and source records attributed to S. V. Bolokhov.

At least 19 recordsLinked to original sources
arXiv2026

Quasinormal modes in the field of a dyon-like dilatonic black hole corresponding to $A_1 + A_1$ Toda chain

We explore the quasinormal modes of a massless test scalar field in the gravitational background of a non-extremal dilatonic dyonic black hole. The dyon-like black hole solution is considered within a four-dimensional gravitational model that includes two scalar fields and two 2-forms. It is governed by two dilatonic coupling vectors $\vecλ_s$ (with $s=1,2$) that satisfy $\vecλ_1 = \vecλ_2 = \vecλ$ and $\vecλ^2 = 1/2$. We derive and examine the quasinormal modes of a massless scalar test field in the eikonal limit. These modes are governed by the solution parameters $μ> 0$, $P_1 > 0$, and $P_2 > 0$. In the two limiting scenarios -- namely $P_1 = P_2 = 0$ and $P_1 = P_2 = P > 0$ -- our results reduce exactly to the known (eikonal) quasinormal spectra for the Schwarzschild and Reissner-Nordström black holes, respectively. Numerical higher-order WKB analysis of quasinormal frequencies for two lower levels (for various values of parameters) is also presented.

gr-qc↗
arXiv2026

Long-lived quasinormal modes of Asymptotically de Sitter Black Holes in Generalized Proca Theory

Massive scalar perturbations of asymptotically de Sitter black holes in generalized Proca theory display a sharp interplay between primary hair, horizon structure, and field mass. Using high-order WKB calculations supplemented by time-domain evolution, we analyze representative black-hole backgrounds and compare the full black-hole spectrum with the exact pure de Sitter benchmark. We show that increasing the scalar mass drives the frequencies into a simple large-mass regime in which the real part grows linearly while the damping rate approaches a nonzero geometry-dependent constant, so true quasi-resonances do not occur within the regime studied here. We also identify how the spectrum shifts with black-hole size and Proca hair, derive a compact analytic large-$μ$ formula, and comment on the implications of the de Sitter-like sector for strong cosmic censorship in the charged three-horizon regime.

gr-qc↗
arXiv2026

Massive Scalar Quasinormal Modes, Greybody Factors, and Absorption Cross Section of a Parity-Symmetric Beyond-Horndeski Black Hole

We study quasinormal modes, greybody factors, and the absorption cross section of a massive scalar field in the asymptotically flat parity-symmetric beyond-Horndeski black-hole background. The scalar mass raises the asymptotic level of the effective potential and can eliminate its barrier peak, thereby changing both the ringing spectrum and the scattering characteristics relative to the massless case. Using Padé-improved high-order WKB calculations together with time-domain evolution, we find that the damping rate decreases strongly as the field mass increases, indicating the approach to long-lived quasi-resonant states for representative parameter families. At the same time, in the large-mass regime these weakly damped modes become progressively harder to isolate in the time domain, because the oscillatory massive tails are expected to dominate on the Koyama--Tomimatsu scale $μ_s t\gg μ_s M$, which is comparatively early when $M=1$ and $μ_s$ is not small. The time-domain profiles also exhibit the transition from quasinormal ringing to an oscillatory late-time tail. Interpreting the same effective potential semiclassically, we show that increasing the scalar mass suppresses low-frequency transmission and shifts the onset of efficient absorption to higher frequencies, while larger deviations from the Schwarzschild limit enhance the absorption cross section. These results show that the competition between long-lived modes and rapidly dominant massive tails makes the massive sector an especially subtle and sensitive probe of the interplay between field mass and geometric deformation in this class of black holes.

gr-qc↗
arXiv2026

Scattering of scalar, electromagnetic, and Dirac fields in an asymptotically flat regular black hole supported by primordial dark matter

We study grey-body factors and absorption cross sections for massless scalar, electromagnetic, and Dirac fields in the exact asymptotically flat regular black-hole geometry supported by a phantom Dirac--Born--Infeld scalar. In the black-hole branch all three sectors are governed by single-barrier effective potentials, which allows a direct 6th-order WKB treatment of the scattering problem and a comparison with the recent quasinormal-mode/grey-body-factor correspondence. We show that increasing the regularity parameter lowers the barriers, shifts transmission to lower frequencies, and enhances the absorption cross sections in all three sectors. By comparing the direct WKB grey-body factors with those reconstructed from the lowest quasinormal modes, we explicitly test the QNM/GBF correspondence and find good agreement, typically at the level of $10^{-2}$ or better.

gr-qc↗
arXiv2026

On gravitating dyonic configurations in nonlinear electrodynamics

We consider static, spherically symmetric configurations of nonlinear electromagnetic fields with Lagrangians $L(f)$, where $f = F_{μν} F^{μν}$, in general relativity (GR) and other metric theories of gravity. The corresponding exact solutions are well known in the framework of GR in cases where only an electric charge ($q_e$) or a magnetic charge ($q_m$) are present, but only a few solutions in particular examples of $L(f)$ are known for dyonic systems with both nonzero $q_e$ and $q_m$. We study the properties of such systems in the special case of equal electric and magnetic charges and, assuming a correct Maxwell limit of $L(f)$, show that there always exists such a configuration of the electromagnetic field that the invariant $f$ is zero in the whole space. It leads to the existence of the corresponding families of solutions both in GR in the presence of other sources of gravity (like fluids or scalar fields) and in a wide range of extended theories of gravity (e.g., scalar-tensor and $F(R)$ gravity), in which the nonlinear electromagnetic field behaves in an especially simple manner.

gr-qc↗
arXiv2026

Quasi-resonances in the vicinity of Einstein-Maxwell-dilaton black hole

We study massive scalar quasinormal spectra of charged Einstein--Maxwell--dilaton black holes by combining high-order WKB--Padé calculations with time-domain evolution. The two approaches show close agreement in the regime where both methods are reliable, allowing controlled tracking of spectral trends across different charges and dilaton couplings. We find that increasing scalar-field mass can strongly suppress damping for several branches, signaling an approach to quasi-resonant, very long-lived oscillations. Although WKB is not expected to determine modes extremely close to the real-frequency axis with high precision, the onset of this regime is clear and appears for multiple dilaton couplings, with additional near-resonant behavior in lower-multipole sectors. The dilaton-induced shifts are substantially larger than the estimated numerical uncertainty, indicating that quasi-resonances are a robust physical signature relevant for ringdown spectroscopy in scalar-extended gravity.

gr-qc↗
arXiv2026

Quasinormal Modes and Grey-Body Factors of Scalar, Electromagnetic and Dirac Fields Around Einasto-Supported Regular Black Holes

We study quasinormal modes and grey-body factors of scalar, electromagnetic and Dirac test fields for a black hole surrounded by matter distributed according to the Einasto density profile. The quasinormal spectrum is calculated using the high-order WKB method with Padé approximants and checked by the time-domain integration. For small values of the Einasto index $\tilde n=1/2$ and $\tilde n=1$, the fundamental modes remain close to their Schwarzschild values, while for $\tilde n=5$ the oscillation frequency increases and the damping rate decreases as the halo parameter grows. Grey-body factors are much less sensitive to the halo environment: the main effect is a mild suppression at low frequencies caused by a moderate increase of the effective potential near the horizon. At higher frequencies the transmission probabilities remain close to the Schwarzschild case.

gr-qc↗
arXiv2025

Revisiting black holes in dark-matter halos: on consistent solutions to the Einstein equations

A number of recent papers have claimed to construct solutions of Einstein's equations describing black holes surrounded by dark-matter halos with empirically motivated density profiles such as the Navarro-Frenk-White, Burkert, Einasto, pseudo-isothermal, and solitonic distributions. We show that the approach used to obtain many of these metrics generically does not lead to the correct solutions to the Einstein equations for the matter sources they purport to represent. This issue originates from applying the Newtonian relation between the tangential velocity and the enclosed mass directly within a relativistic framework, followed by the ad hoc assumption $g(r)=f(r)$ for the metric functions. This procedure leads to an anisotropic fluid with $P_r=-ρ$ and $P_t=-rρ'/2-ρ$, whose density differs from the claimed halo profile and often becomes non-physical near the horizon, violating the weak energy condition. As a result, the obtained spacetimes do not describe black holes embedded in known galactic halos but rather distinct anisotropic configurations unrelated to the intended matter distribution. We demonstrate this problem on several representative examples from the literature, including metrics based on the NFW, Burkert, Einasto, solitonic, pseudo-isothermal, and Dehnen-(1,4,5/2) profiles, as well as the case of the NGC~4649 halo. For each case, the correct Einstein-consistent form of the metric and the associated physical interpretation are provided. Our analysis clarifies the limits of validity of the Newtonian approximation near compact objects and establishes a consistent framework for constructing dark-matter-inspired black-hole geometries within General Relativity.

gr-qc↗
arXiv2025

Quasinormal ringing of a regular black hole sourced by the Dehnen-type distribution of matter

We study quasinormal modes of test scalar, electromagnetic, and Dirac fields in the background of a new analytic regular black-hole solution obtained as an exact solution of the Einstein equations sourced by a Dehnen-type matter distribution in [R. A. Konoplya, A. Zhidenko, arXiv:2511.03066]. The metric is asymptotically flat and characterized by a simple lapse function $f(r)=1-2 M r^{2}/(r+a)^{3}$, where $M$ is the ADM mass and $a$ represents the characteristic scale of the surrounding dark-matter halo that regularizes the central region. The effective potentials for all perturbing fields possess the standard single-barrier form, ensuring linear stability and the applicability of the WKB formalism. The quasinormal frequencies are computed using the sixth- and ninth-order WKB methods with Padé corrections and verified by time-domain integration, both approaches showing excellent agreement. The parameter $a$ leads to a moderate increase in the real oscillation frequency, while the damping rate remains almost unchanged, producing only small corrections to the Schwarzschild spectrum. Since such deviations become appreciable only for unrealistically dense halos, our results confirm that the quasinormal spectrum of astrophysical black holes is safely unaffected by ordinary galactic dark-matter environments.

gr-qc↗
arXiv2025

Photon spheres near black holes in a model with anisotropic fluid

The semi-review paper studies the null geodesics which appear for black hole solutions in the gravitational $4d$ model with anisotropic fluid. The equations of state for the fluid and solutions itselves depend upon integer parameter $q = 1, 2, ...$: $p_r = -ρc^2 (2q-1)^{-1}, \quad p_t = - p_r$, where $ρ$ is the mass density, $c$ is speed of light, $p_r$ and $p_t$ are pressures in radial and transverse to radial directions, respectively. The circular null geodesics are explored and the master equation for radius $r_*$ of photon sphere is outlined as well as the proposition on existence and uniqueness of the solution to master equation obeying $r_* > r_h$, where $r_h$ is horizon radius. The relations for spectrum of quasinormal modes for a test massless scalar field in the eikonal approximation are overviewed and compared with cyclic frequencies of circular null geodesics. The shadow angles are explored.

gr-qc↗
arXiv2025

Gravitational quasinormal modes of the Hayward spacetime

We study gravitational quasinormal modes of the Hayward spacetime, a regular black-hole geometry that also admits an interpretation as an effective quantum-corrected solution within asymptotically safe gravity. Using both the higher-order WKB method supplemented with Pade approximants and time-domain integration with Prony analysis, we obtain accurate spectra for axial perturbations and explore the impact of the quantum parameter $γ$. We find that increasing $γ$ systematically raises the oscillation frequencies while reducing the damping rates, making the ringdown longer lived. For the first overtone, the effect of $γ$ is noticeably stronger than for the fundamental mode, providing an indication of the so-called outburst of overtones previously observed for test fields, and pointing to the particular sensitivity of subdominant modes to near-horizon quantum corrections. In addition, the analytic approximation for quasinormal modes are obtained in the form of expansion beyond the eikonal limit.

gr-qc↗
arXiv2025

Gravitational Quasinormal Modes and Grey-Body Factors of Bonanno-Reuter Regular Black Holes

We study gravitational perturbations of the Bonanno--Reuter quantum-corrected black hole arising in the asymptotic safety scenario, focusing on QNMs and grey-body factors. Assuming the RG parameter $\tildeω$ is fixed to its phenomenologically motivated value, we treat the interpolation parameter $γ$ as free and investigate how it modifies the black hole's response to axial gravitational perturbations. Quasinormal frequencies are computed using the sixth-order WKB method with Padé approximants, and their dependence on $γ$ and the black hole mass $M$ is analyzed. We find that the Schwarzschild limit is rapidly recovered for large $M$ or large $γ$, while significant deviations arise in the quantum regime. The accuracy of the WKB results is confirmed by time-domain integration of the wave equation. Comparison of grey-body factors computed via both the WKB method and the quasinormal mode correspondence are in a good concordance. Our findings indicate that quantum corrections can leave significant imprints in the ringdown and radiation spectra, while preserving consistency with classical results in the appropriate limit.

gr-qc↗
arXiv2025

Overtones' outburst and Hawking evaporation of Kazakov-Solodukhin quantum corrected black hole

The Kazakov-Solodukhin black hole metric represents a spherically symmetric deformation of the Schwarzschild solution due to quantum-gravity corrections. Assuming the absence of nonspherical deformations of the metric, this problem was solved nonperturbatively. In this study, we investigate the intensity of Hawking radiation in the background of such quantum-corrected black holes and the behavior of their quasinormal modes (QNM). Our findings indicate that while the geometry and such classical characteristics as the fundamental QNM frequencies or the shadow radius are only slightly altered, the Hawking radiation and the frequencies of QNM overtones of sufficiently small black holes change much more significantly. This Hawking radiation enhancement arises due to much larger grey-body factors, while the Hawking temperature remains unaffected. The effect becomes significant at the latest stage of black hole evaporation.

gr-qc↗
arXiv2025

Review of analytic results on quasinormal modes of black holes

We present a concise review of known analytic results for quasinormal modes of black holes and related spacetimes. Our emphasis is on those regimes where the perturbation equations admit exact or perturbative solutions, providing insights complementary to numerical or semi-analytic approaches. We discuss solvable cases in lower-dimensional spacetimes, algebraically special modes, and exact results in higher-curvature gravity theories. Particular attention is given to the eikonal regime and its correspondence with null geodesics, as well as to beyond-eikonal approximations based on inverse multipole expansions in parametrized metrics. We review analytic solutions obtained in the near-extremal limit of Schwarzschild - de Sitter black holes, in the regime of large field mass, and in pure de Sitter and anti - de Sitter spacetimes, where boundary conditions play a crucial role. While not exhaustive, this overview highlights the diversity of techniques and physical insights made possible by analytic treatments of quasinormal spectra.

gr-qc↗
arXiv2024

Circumventing Quantum Gravity: Black Holes Evaporating into Macroscopic Wormholes

Recently, metrics that describe regular black holes, extreme black holes, or traversable wormholes have been widely discussed. These spacetimes, appearing in scenarios such as the brane world, are contingent on the values of the parameters, with each metric encompassing all three objects. We are considering various known models for these black hole/wormhole interpolating spacetimes and showing that, starting from the macroscopic black holes, all of them must evaporate into macroscopic wormholes, thus avoiding existential problems related to the final stages of black hole evaporation and issues of quantum gravity and black hole remnants. For this purpose, we are calculating the energy emission rates of black holes and the appropriate lifetimes. We argue that some of our conclusions should hold regardless of the specific model, as long as it permits an extremal black hole state with zero temperature at a particular value of the coupling constant.

gr-qc↗
arXiv2024

A regular center instead of a black bounce

The widely discussed ``black-bounce'' mechanism of removing a singularity at $r=0$ in a spherically symmetric space-time, proposed by Simpson and Visser, consists in removing the point $r=0$ and its close neighborhood, resulting in emergence of a regular minimum of the spherical radius that can be a wormhole throat or a regular bounce. Instead, it has been recently proposed to make $r=0$ a regular center by properly modifying the metric, still preserving its form in regions far from $r=0$. Different algorithms of such modifications have been formulated for a few classes of singularities. The previous paper considered space-times whose Ricci tensor satisfies the condition $R^t_t =R^r_r$, and regular modifications were obtained for the Schwarzschild, Reissner-Nordström metrics, and two examples of solutions with magnetic fields obeying nonlinear electrodynamics (NED). The present paper considers regular modifications of more general space-times, and as examples, modifications with a regular center have been obtained for the Fisher (also known as JNW) solution with a naked singularity and a family of dilatonic black holes. Possible field sources of the new regular metrics are considered in the framework of general relativity (GR), using the fact that any static, spherically symmetric metric with a combined source involving NED and a scalar field with some self-interaction potential. This scalar field is, in general, not required to be of phantom nature (unlike the sources for black bounces), but in the examples discussed here, the possible scalar sources are phantom in a close neighborhood of $r=0$ and are canonical outside it.

gr-qc↗
arXiv2024

Late time decay of scalar and Dirac fields around an asymptotically de Sitter black hole in the Euler-Heisenberg electrodynamics

We compute the quasinormal modes of massive scalar and Dirac fields within the framework of asymptotically de Sitter black holes in Euler-Heisenberg non-linear electrodynamics. We pay particular attention to the regime $μM/m_{P}^2 \gg 1$, where $μ$ and $M$ denote the masses of the field and the black hole, respectively, and $m_{P}$ represents the Planck mass, covering a range from primordial to large astrophysical black holes. Through time-domain integration, we demonstrate that, contrary to the asymptotically flat case, the quasinormal modes also dictate the asymptotic decay of fields. Employing the 6th order WKB formula, we derive a precise analytic approximation for quasinormal modes in the regime $μM/m_{P}^2 \gg 1$ without resorting to expansion in terms of the inverse multipole number. This analytic expression takes on a concise form in the limit of linear electrodynamics, represented by the Reissner-Nordström black holes.

gr-qc↗