arXiv subjects

Javlon Rayimbaev

Publications and source records attributed to Javlon Rayimbaev.

At least 19 recordsLinked to original sources

arXiv2026

Kerr-referenced analytical parametrization of rotating black holes in dynamical Chern-Simons gravity

Rotating black holes in dynamical Chern-Simons gravity are known nonperturbatively mainly through numerical solutions, which limits their direct use in strong-field applications. We construct a Kerr-referenced analytical parametrization of the near-general-relativistic numerical branch using a compact radial coordinate, low-order angular multipoles, and continued fractions. The resulting two-parameter family accurately reproduces the numerical metric throughout the validated weak-coupling and moderate-spin domain. Independent off-grid solutions confirm that the parametrization retains its accuracy away from the calibration set. We further assess the model through equatorial light rings, critical impact parameters, and full two-dimensional null-geodesic ray tracing without assuming separability. The resulting shadow observables closely match those obtained from the numerical geometries. This parametrization therefore provides a practical analytical metric for geodesic and strong-field calculations without relying on a slow-rotation expansion.

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arXiv2026

Blandford-Znajek Scaling in a Power-Law Rotating Kalb-Ramond Geometry: Magnetic-Flux Systematics and Bayesian Identifiability

Relativistic jets from spinning black holes offer a possible strong-field probe of gravity through the Blandford-Znajek mechanism. We study the leading jet-power scaling in the four-dimensional power-law rotating Kalb-Ramond geometry introduced by Kumar, Ghosh, and Wang. The metric is used here as a stationary background, without assuming that it constitutes a newly established exact rotating solution. We first examine the deformation at the metric level. For $s=2$ it is absorbed completely by a mass redefinition, whereas for $s>2$ the correction decays more slowly than the usual mass term. Our main benchmark is therefore the nondegenerate $s=3/2$ case, whose correction falls faster than the Kerr mass term; $s=3$ is kept as a secondary comparison. We evaluate the BZ scaling under three magnetic assumptions: fixed total horizon flux, fixed local normal field with the proper horizon area, and a reduced radius-based flux proxy. The resulting trends differ appreciably, showing that the magnetic prescription is itself a leading systematic. For GRO J1655-40 and GRS 1915+105, the marginalized deformation posterior remains close to the horizon-conditioned effective prior for both a uniform prior and a truncated-Gaussian alternative. The jet-only profile likelihood is also nearly flat over the allowed deformation range, with the same qualitative behavior in the $s=3$ test. Thus, within the present setup, the jet-power proxies do not independently determine the Kalb-Ramond deformation. A stronger inference will require better control of the rotating background, source-dependent magnetic flux, non-Kerr spin estimates, and a larger sample.

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arXiv2026

Periodic orbits and gravitational wave signatures from magnetic dipoles around magnetized Kerr black holes

We study periodic orbits and the associated gravitational radiation of a magnetized (uncharged) test particle carrying a magnetic dipole moment with coupling constant beta, moving in the equatorial plane of a rotating, magnetized Kerr black hole immersed in an external asymptotically uniform magnetic field, starting from the effective potential derived for such particles. We compute the marginally bound orbit (MBO) and the innermost stable circular orbit (ISCO) as functions of the black hole spin a and the magnetic coupling beta, and map out the allowed region of the orbital energy-angular momentum (L, E) plane for bound motion. We then classify periodic orbits using the topological zoom-whirl scheme of Levin and Perez-Giz, characterized by three integers (z,w,v) through the rational rotation number q=w+v/z, and construct a family of closed rosette orbits at fixed angular momentum. Using the numerical-kludge, restricted-quadrupole approximation for an extreme-mass-ratio inspiral consisting of a stellar-mass magnetized secondary orbiting a supermassive magnetized Kerr black hole, we compute the time-domain gravitational waveforms h_+(t), h_\times(t) produced by these periodic orbits and their frequency-domain characteristic strain, and compare the latter with the anticipated instrumental sensitivity curves of LISA, Taiji and TianQin. We find that the magnetic coupling \beta systematically shifts the MBO and ISCO outward and lowers their orbital energy and angular momentum, that the zoom-whirl structure of the periodic orbits is imprinted directly on the burst-like morphology of the emitted waveform, and that the resulting gravitational-wave signals fall within the sensitivity band of upcoming space-based detectors for suitably close and massive sources.

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arXiv2026

Circular-orbit dynamics and QPO constraints in static Einstein--scalar--Gauss--Bonnet black holes

Einstein--scalar--Gauss--Bonnet (EsGB) gravity provides a physically motivated framework for testing strong-field deviations from the Schwarzschild geometry through scalar hair. We study neutral-particle circular motion and high-frequency quasi-periodic oscillations (HF-QPOs) in static EsGB black holes described by a continued-fraction metric with a single dimensionless deformation parameter $p$ on the Schwarzschild-connected quadratic-coupling branch. We determine the effective potential, circular-orbit energy and angular momentum, characteristic radii, and orbital and radial epicyclic frequencies, and apply the relativistic precession model to twin-peak QPO data from XTE J1550--564, GRO J1655--40, GRS 1915+105, and M82 X-1. A source-by-source Markov chain Monte Carlo analysis shows that the observed frequency pairs can be reproduced within their uncertainties and that the radial epicyclic frequency carries the main model-level sensitivity to $p$. However, a controlled prior-sensitivity analysis using uniform and truncated Gaussian priors finds that the marginal posterior of $p$ closely follows the adopted prior for all four sources. This reflects the intrinsic underconstraint of fitting three correlated parameters $(M,p,r)$ to two measured frequencies. The inferred intervals therefore represent model-dependent compatibility regions rather than an independent measurement or preferred value of the EsGB deformation. The static results provide a baseline for future rotating and multi-observable tests.

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arXiv2026

Tidal Deformability of Neutron Stars in Bumblebee Gravity: Probing Lorentz Symmetry Breaking with Gravitational Waves

We investigate the tidal properties of static neutron stars in the Neves--Gardim branch of bumblebee gravity, a vector--tensor theory in which a nonzero vacuum expectation value of the bumblebee field spontaneously breaks local Lorentz symmetry. The stellar background is determined from the full modified Tolman--Oppenheimer--Volkoff system, including the term containing $m''(r)$. For a differentiable barotropic equation of state, this system is recast into an algebraically equivalent first-order form without discarding any bumblebee-dependent contribution. Because a complete coupled derivation of static even-parity metric and bumblebee-field perturbations is not presently available for this stellar branch, the tidal sector is treated through an explicit effective metric-deformation prescription: the Hinderer fluid perturbation equation is evaluated on the modified bumblebee background, and the standard surface matching relation is retained as part of the same prescription. We compute the quadrupolar tidal Love number $k_2$ and the dimensionless tidal deformability $\Lambda=(2/3)k_2\mathcal{C}^{-5}$ for the BSk20, BSk21, DD2, and MS1 equations of state over $\ell\in[-0.4,+1.0]$. The general-relativistic limit is recovered at $\ell=0$ to within $0.2\%$ in the benchmark calculations. Within the adopted effective prescription, comparison with the GW170817 binary tidal-deformability bound $\widetilde{\Lambda}\leq720$ yields the EOS-dependent limiting values $\ell_{\max}=+0.25$ (BSk20), $+0.06$ (BSk21), $-0.09$ (DD2), and $-0.25$ (MS1). These tidal limits are conditional on the stated perturbative prescription and should be reassessed when the complete linearised vector--tensor problem becomes available.

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arXiv2026

Role of spin-curvature and magnetic interactions on circular orbits of particles with magnetic monopole around Bardeen black holes

We investigate the dynamics of magnetically charged spinning test particles in the spacetime of the Bardeen regular black hole, sourced by nonlinear electrodynamics and featuring a magnetic monopole charge parameter g. Employing the Mathisson-Papapetrou-Dixon equations supplemented by the Tulczyjew spin condition and extended to include magnetic interactions via the generalized Lorentz force, we derive the effective potential governing the radial motion in the equatorial plane. We analyze the properties of circular orbits, including the location and parameters of the innermost stable circular orbit, and examine how they are modified by the particle's spin s, specific magnetic charge lambda, and the black hole's magnetic charge g. Prograde spin and attractive magnetic interactions reduce the ISCO radius, whereas repulsive interactions and retrograde spin shift it outward. We further impose timelike constraints to exclude unphysical superluminal trajectories, delineating the admissible parameter space. Finally, we explore high-energy particle collisions near the horizon, computing the critical angular momentum and the center-of-mass collision energy. Due to the regular core of the Bardeen spacetime, the Ba\~nados-Silk-West effect is significantly suppressed or capped at finite values, in contrast to singular black hole solutions. These results highlight distinctive phenomenological signatures of regular black holes and offer potential observational probes of nonlinearity in electrodynamics and of magnetic monopoles through accretion processes, extreme-mass-ratio inspirals, and ultra-high-energy particle interactions.

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arXiv2026

Corrected thermodynamics and radiation predictions of modified black bounce compact objects

We study the thermodynamic properties and radiation characteristics of a regular compact object obtained by applying the Simpson-Visser (SV) regularisation to the Schwarzschild modified gravity black hole. The resulting SV-MOG spacetime, whose lapse function involves both the MOG coupling parameter alpha and the black-bounce parameter l, smoothly interpolates between a regular black hole, a one-way wormhole, and a traversable wormhole depending on the parameter l. We derive the Hawking temperature and heat capacity for the black hole branch, identifying second-order phase transitions signaled by sign changes in CV, and, for the horizonless wormhole branch where no causal horizon and hence no genuine Hawking radiation exists we instead construct a physically well-defined effective temperature from the Lyapunov exponent of the unstable photon sphere. Quantum gravitational corrections to the entropy are incorporated via logarithmic terms parameterized by coefficients beta1, beta2, whose theoretically preferred ranges in loop quantum gravity and string theory we discuss, and we show that deviations from the Bekenstein-Hawking area law become significant at small horizon radii. A linear scalar-perturbation analysis further shows that the effective radial potential remains non-negative throughout the black-hole exterior and across the wormhole throat, indicating stability against monopole perturbations independently of the thermodynamic stability inferred from the heat capacity.

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arXiv2026

Gravitational perturbations of a regular T-duality inspired black hole: Quasinormal modes, excitation factors, and time-domain evolution

We study axial gravitational perturbations of the neutral regular black hole generated by a non-local, T-duality-inspired zero-point length and the associated gravitational self-energy. In this geometry, the usual point source is replaced by a regular core, and the zero-point length controls the departure from the Schwarzschild limit. We compute the fundamental quasinormal modes and several overtones using high-order WKB--Pad\'e methods, and we verify the dominant mode via direct time-domain evolution. When the zero-point length is turned on, the real parts of the ADM-scaled frequencies increase for the gravitational modes with $\ell=2,3,4$, so the ringdown oscillates faster than in the Schwarzschild limit. The damping rates change more gradually: they initially increase slightly and then decrease near the largest deformation values considered here. This behavior is consistent with the effective potential, whose barrier becomes higher as the deformation parameter increases. We also compute the corresponding excitation factors and find that their magnitudes vary much less strongly than the quasinormal frequencies.

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arXiv2026

Particle dynamics and quasi-periodic oscillations of a Reissner--Nordstr\"om-like black hole in Kalb--Ramond gravity under an external magnetic test field

We investigate the dynamics of charged test particles and quasi-periodic oscillations around a Reissner--Nordstr\"om-like black hole in Kalb--Ramond (KR) gravity in the presence of an external magnetic test field. The KR background introduces a Lorentz-violating parameter $\ell$, which modifies the spacetime geometry, horizon structure, circular orbits, and characteristic frequencies of particle motion. In contrast to the standard Wald-type prescription, the magnetic-field configuration is constructed from the source-free Maxwell equation on the charged KR background, allowing the magnetic profile to be consistently adapted to the modified geometry. We derive the equations of motion, the effective potential, the conditions for circular orbits, and the orbital and radial epicyclic frequencies of charged particles. The results show that the black-hole charge $Q/M$, the KR parameter $\ell$, the specific particle charge $\epsilon$, and the magnetic coupling $\beta=bM$ jointly affect the innermost stable circular orbit (ISCO) and the quasi-periodic oscillation (QPO) frequencies. We then apply the obtained frequencies to the relativistic precession model, where the upper QPO frequency is identified with the orbital frequency and the lower one with the periastron-precession frequency. Using the observed twin-peak QPO data of GRO J1655--40, XTE J1550--564, and M82 X-1, we perform a Markov chain Monte Carlo analysis to constrain the model parameters. The obtained posterior constraints indicate that the charged KR black-hole model with an external magnetic field can consistently reproduce the observed QPO pairs within the adopted parameter ranges. These findings suggest that QPO observations may serve as a useful phenomenological tool for probing Lorentz-violating black-hole geometries and electromagnetic effects in strong-gravity environments.

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arXiv2026

Eikonal Ringing, Shadows, Lensing, Grey-Body Factors, and Binding Energy of Asymptotically Flat Regular Black Holes in Phantom Dirac-Born-Infeld Gravity

We develop a geodesic-optics description of eikonal quasinormal ringing, blackhole shadows, strong lensing, grey-body factors (GBFs), and the binding energy of massive particles for the asymptotically flat regular black-hole geometry obtained in phantom Dirac-Born-Infeld (DBI) gravity. The null-orbit structure admits an especially compact analytic treatment. The unstable photon orbit remains at the Schwarzschild-like coordinate radius throughout the black-hole branch, while the orbital frequency and Lyapunov exponent coincide exactly. Consequently, eikonal quasinormal modes (QNMs), shadow radius, GBFs, and strong-deflection observables are all governed by a single dimensionless function of the core-size parameter. For timelike circular motion, we derive exact expressions for the specific energy and angular momentum, obtain the innermost stable circular orbit (ISCO) condition in closed implicit form, and show that the ISCO binding efficiency decreases as the regular core grows. We present illustrative plots for the exact geodesic invariants, the corresponding grey-body profiles, and the timelike binding-energy curves. The resulting construction provides an exact one-parameter bridge between the regular black-hole metric and its leading geodesic observables.

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arXiv2026

Greybody Factors, Absorption Cross Sections and Hawking Radiation of Holonomy-Corrected Schwarzschild Black Holes

We study greybody factors, absorption cross sections and Hawking energy-emission rates for minimally coupled massless scalar, electromagnetic and massless Dirac test fields on the loop-quantum-gravity-inspired holonomy-corrected Schwarzschild black hole. The geometry is controlled by a dimensionless holonomy parameter, and the radial wave equations are solved by direct numerical integration with first- and sixth-order WKB estimates as complementary checks. The scalar, electromagnetic and Dirac channels respond differently: the dominant scalar mode becomes more transparent, the electromagnetic threshold shifts slightly upward, and the dominant Dirac mode is only mildly modified. The scalar absorption cross section retains the universal low-frequency limit, the electromagnetic cross section changes mainly in the infrared, and the Dirac cross section develops a strongly suppressed low-frequency tail. Since the Hawking temperature falls monotonically, thermal suppression dominates the radiative output. Thus the holonomy correction enhances low-lying scalar transmission but suppresses Hawking radiation overall, with the electromagnetic sector most strongly quenched and the fermionic sector dominant once $\alpha$ is appreciable.

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arXiv2026

Grey-Body Factors and Thermodynamics of Asymptotically de Sitter Black Holes in Generalized Proca Theory

Generalized Proca theory supplements gravity with a massive vector field whose derivative self-interactions can support black holes carrying primary vector hair. In the asymptotically de Sitter branch considered here, the de Sitter scale is effective: it is generated by the vector sector rather than imposed through a bare cosmological-constant term. We compute grey-body factors and effective absorption cross-sections for massive scalar, electromagnetic, and massless Dirac test fields on this background. The transmission curves are obtained from a sixth-order WKB barrier calculation and are compared with the quasinormal-mode reconstruction; the two descriptions mostly agree, with small visible differences at lower mutlipoles. Increasing the scalar mass raises and broadens the scalar barrier, suppresses transmission at fixed frequency, and shifts efficient transmission to higher frequencies. The couplings considerably affect the grey-body factors and black hole thermodynamics.

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arXiv2026

Bardeen spacetime as quantum corrected black hole: Grey-body factors and quasinormal modes of gravitational perturbations

We study axial gravitational perturbations of the asymptotically flat Bardeen spacetime interpreted as a string-T-duality-inspired quantum-corrected Schwarzschild black hole. Starting from the anisotropic-fluid background, we derive the Regge--Wheeler-type master equation and the corresponding effective potential, and compute quasinormal modes with high-order WKB--Pad\'e and time-domain methods. We show that increasing the quantum-correction scale $\ell_0$ raises and shifts the barrier inward, causing the black hole to ring at higher frequencies and decay more slowly. The same deformation suppresses low-frequency transmission, shifts the onset of grey-body factors to larger frequencies, and reorganizes the partial and total absorption cross-sections. Overall, the results identify a clear and consistent imprint of short-distance regularization on both ringdown and scattering observables.

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arXiv2026

A First-Order Eikonal Framework for Quasinormal Modes, Shadows, Strong Lensing, and Grey-Body Factors in a Scalarized Black-Hole Metric

We construct an analytic geodesic-optics description of quasinormal ringing, black-hole shadows, strong lensing, and grey-body factors for the static spherical metric introduced in [Bakopoulos, et. al. arXiv:2310.11919]. Working in a weak-hair regime, we derive closed first-order formulas for the photon-sphere radius, orbital frequency, and Lyapunov exponent. These invariants are then employed within the Schutz--Will WKB approach to obtain eikonal quasinormal frequencies, mapped to shadow and strong-deflection observables through exact identities for static spherical geometries, and used to build a closed analytic form for the transmission probability. At leading eikonal order, these relations are controlled by null geodesics and are therefore spin-universal for test scalar/electromagnetic/gravitational sectors, up to subleading corrections. Besides the standard ringdown--shadow correspondence, we present three additional results: (i) an explicit quality-factor correction, (ii) limiting core-size expansions that show when damping ratios are nearly insensitive to the scalarized core, and (iii) a comparative study of grey-body factors for moderate multipoles and several core-size ratios. The resulting construction provides a concise one-parameter connection from the metric function to ringdown, lensing, and scattering observables.

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arXiv2026

Josephson Effects in Slowly Rotating Spacetimes

We investigate Josephson phenomena in a slowly rotating stationary spacetime, emphasizing the distinct roles of gravitational redshift and rotational frame dragging motivated by [10.1007/JHEP02(2026)006]. Using a covariant formulation based on gauge-invariant phase dynamics and conserved currents within a $3+1$ decomposition, we analyze both AC and DC Josephson effects and interferometric configurations. Restricting attention to linear order in the rotation parameter $a$, and working in the Eulerian/ZAMO frame, we show that in the slow-rotation slicing adopted here the lapse function agrees with its static (Schwarzschild-type) form up to $\mathcal{O}(a^2)$, while rotational effects enter through the shift vector. Consequently, redshift effects on Josephson frequencies and DC critical currents remain unchanged relative to the non-rotating case at $\mathcal{O}(a)$. The AC Josephson relation retains its redshifted structure when expressed in terms of proper voltages and reduces to the standard flat-spacetime form when formulated in terms of asymptotic (Killing-time) observables. Likewise, the DC critical current measured at infinity scales with a single power of the lapse function and is unaffected by rotation at linear order in the absence of azimuthal condensate momentum. Rotational effects become relevant only in configurations sensitive to spatial phase transport or to synchronization with respect to the global time coordinate. In particular, RF-driven interferometric setups can acquire Sagnac-type phase offsets associated with frame dragging, whereas the DC fluxoid constraint remains unshifted at linear order in the present approximation. Our results provide a clean separation between lapse-driven redshift effects and shift-driven rotational contributions in Josephson physics and furnish a consistent framework for superconducting circuits in stationary spacetimes.

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arXiv2026

Ringing Regularity: Gravitational Perturbations and Quasinormal Modes of Einasto-Supported Black Holes

We investigate axial gravitational perturbations and quasinormal modes of regular black holes supported by an Einasto distribution of matter. Halo matter not only removes the central singularity but also modifies the quasinormal spectrum. We show that the resulting quasinormal spectrum deviates systematically from the Schwarzschild case, with shifts in both oscillation frequencies and damping rates that grow with the halo scale parameter and the Einasto index. In near-extremal configurations, the damping rate can be significantly suppressed, leading to long-lived modes. The effects of regularity and environmental factors on the spectrum are found to be substantially larger than the estimated numerical uncertainty, as confirmed independently by high-order WKB calculations with Pad\'e resummation and time-domain integration.

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arXiv2026

Two types of quasinormal modes of Casadio-Fabbri-Mazzacurati brane-world black holes

Using the convergent Leaver method, we investigate the quasinormal modes of a massive scalar field propagating in the background of the Casadio--Fabbri--Mazzacurati (CFM) brane-world black hole. We show that the spectrum exhibits two distinct types of modes, depending on their behavior as the field mass increases. In one class, the real oscillation frequency decreases and eventually approaches zero, while in the other the damping rate tends to vanish. When either the real or imaginary part of the frequency reaches zero, the corresponding mode disappears from the spectrum, and the first overtone replaces it. The emergence of modes with a vanishing real part at certain critical values of the field mass is a distinctive feature of the CFM spectrum.

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arXiv2026

Telling tails and quasi-resonances in the vicinity of Dymnikova regular black hole

We investigate quasinormal modes, late-time tails, and grey-body factors for massive scalar perturbations in the background of the Dymnikova regular black hole. By applying both the time-domain integration and the WKB method with Pad\'e improvements, we show that the spectrum of massive fields differs qualitatively from the massless case. The oscillation frequency of the dominant mode grows with the field mass $\mu$, while the damping rate decreases, suggesting the existence of quasi-resonances at sufficiently large $\mu$. In the time domain, the late-time signal exhibits oscillatory tails with a power-law envelope, whose decay rate matches analytic expectations. Grey-body factors are also computed, showing strong suppression of radiation when mass is increased. Taken together, these results indicate that massive fields provide distinctive signatures of regular black holes and may serve as probes of near-horizon quantum corrections in the Dymnikova geometry.

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