arXiv subjects

Shokhzod Jumaniyozov

Publications and source records attributed to Shokhzod Jumaniyozov.

7 recordsLinked to original sources

arXiv2026

Quasi-periodic oscillations in Letelier black holes within Kalb-Ramond gravity embedded in a uniform external magnetic field

We investigate the dynamics of charged test particles around a Letelier black hole, i.e. a black hole surrounded by a cloud of strings (CoS), in Kalb-Ramond (KR) gravity, immersed in an external, asymptotically uniform magnetic field aligned with the symmetry axis. The geometry depends on the CoS parameter and on the Lorentz-violating KR parameter only through a single combination of the two, so that the two effects can compensate each other and the Schwarzschild metric is recovered when both parameters are equal. Because the spacetime is not Ricci flat, the Wald potential is not a solution of the Maxwell equations; we show that the regular source-free magnetic test field is given in closed form by a Gauss hypergeometric function of the radial coordinate, which reduces to the Wald solution in the Schwarzschild limit. Using this exact field we derive the equations of motion, the effective potential, the circular orbits, the innermost stable circular orbit (ISCO), representative escaping, captured and curled trajectories, and the orbital, radial and vertical epicyclic frequencies in closed form; all frequency expressions are cross-checked against direct numerical integration of the full equations of motion. Within the relativistic precession model, we perform a Markov chain Monte Carlo (MCMC) analysis of the twin-peak high-frequency quasi-periodic oscillations (QPOs) of GRO J1655-40, XTE J1550-564 and GRS 1915+105 for four nested models, complemented by nested sampling to compute Bayesian evidences and to weight the two (Larmor and anti-Larmor) magnetic modes of the posterior. The Schwarzschild model is excluded for GRO J1655-40 and XTE J1550-564, with a difference in the Akaike information criterion of about 110.

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arXiv2026

Magnetically charged spinning particles around a regular black hole: constraints on the monopole charge from quasi-periodic oscillations

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. Using the Mathisson-Papapetrou-Dixon equations with the Tulczyjew spin condition, extended by the Coulomb-like force between the particle's magnetic charge and the monopole, we derive the effective potential for equatorial motion and analyze circular orbits, the innermost stable circular orbit (ISCO), superluminality constraints and high-energy collisions. Solving the ISCO conditions perturbatively around Schwarzschild, we obtain exact coefficients, r_{\rm ISCO}, and show that the magnetic coupling λg shifts r_{\rm ISCO} only at higher order while it changes the ISCO energy and angular momentum at first order. We compute radiative efficiencies (up to \simeq 8\% in the explored range, against 5.72\% for Schwarzschild) and the orbital and radial epicyclic frequencies, including the ISCO and the 3:2 resonance, whose frequency at fixed mass is shifted by 5--11\% for g/M=0.5--0.7.

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arXiv2026

Probing black holes surrounded by Dust field in Quantum Fluctuation Modified Gravity with twin-peak QPOs

We study a static, spherically symmetric black hole solution surrounded by a dust field within quantum fluctuation modified gravity, in which the quantum-fluctuation parameter $α$ and the dust-field strength parameter $K$. The horizon structure reveals the two parameters acting in opposite directions: strengthening $K$ draws the inner and outer horizons together until they merge into a single extremal horizon, while a larger $α$ restores the Schwarzschild limit; the same opposing trend extends to the effective potential and the characteristic circular-orbit radii -- the innermost stable circular orbit, the marginally bound orbit, and the marginal circular orbit -- which shift inward with $K$ and outward with $α$, and to the Keplerian and radial epicyclic frequencies of massive test particles. From these frequencies we build three twin-peak quasi-periodic oscillation models -- relativistic precession, warped-disk, and epicyclic-resonance -- along with their $3{:}2$, $4{:}3$, and $5{:}4$ resonance radii, all following the same $K$-$α$ trend. Testing all three models against twin-peak QPO data from two stellar-mass (GRO~J1655$-$40, XTE~J1550$-$564) and two intermediate-mass (M82~X$-$1, NGC~1313~X$-$1) sources through a Markov Chain Monte Carlo analysis places best-fit constraints, at the $2σ$ level, of $K\in(0,0.5)$ and $α\in(0.3,0.6)$ across all sources and models.

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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

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 βsystematically 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

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--Padé 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

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 $Λ=(2/3)k_2\mathcal{C}^{-5}$ 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 $\widetildeΛ\leq720$ 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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