arXiv subjects

Akbar Davlataliev

Publications and source records attributed to Akbar Davlataliev.

7 recordsLinked to original sources

arXiv2026

Probing scalarized wormholes through quasi-periodic oscillations and spinning particle dynamics

We investigate the dynamics of test particles in a three-parameter scalarized wormhole spacetime within Einstein-scalar field theory. For spinless particles, we derive the orbital and epicyclic frequencies and compute twin-peak QPO spectra using the ER3 and ER4 resonance models. The scalar coupling parameter $g_s$ shifts the innermost stable circular orbit to larger radii and systematically modifies the characteristic 3:2 resonance condition. Extending to spinning particles via the Mathisson-Papapetrou-Dixon formalism, we find that spin-curvature coupling significantly alters the effective potential and innermost stable circular orbit parameters. The maximum physically admissible spin increases monotonically with the scalar coupling. Analysis of particle collisions near the wormhole throat reveals that both scalar coupling and relative spin orientation determine collision energetics, with anti-aligned spin configurations producing substantially higher energies. Our results suggest that the combined effects of scalar coupling and spin-curvature interaction leave distinct imprints on QPO frequencies and collision processes, potentially providing observable signatures for distinguishing scalarized wormholes from standard black holes.

gr-qc↗

arXiv2026

Cosmological Constraints on Minimal Cubic Galileon Models in Teleparallel Gravity

Cubic Galileon cosmological models provide a well-motivated framework for investigating late-time cosmic acceleration beyond the standard $Λ$CDM paradigm. In this work, we study observational constraints on cubic Galileon models within the teleparallel gravity framework, where deviations from the standard teleparallel equivalent of general relativity are encoded through the model parameter $b_1$. We consider two scalar-field potentials, namely quadratic and exponential potentials, and analyze four representative scenarios: quadratic and exponential potentials with $b_1$ treated as a free parameter, together with the corresponding cases in which $b_1=2$ is fixed. Using the $\text{Pantheon}^+$ Type Ia supernova sample, cosmic chronometer measurements, SH0ES information, and baryon acoustic oscillation data, we constrain the cosmological and model parameters and compare the observational viability of the different scenarios. We find that the considered teleparallel cubic Galileon models can accommodate the late-time expansion history, although the statistical preference depends on the choice of potential and on whether $b_1$ is fixed or varied. In particular, the fixed-$b_1$ model with a quadratic potential provides the most competitive fit among the Galileon scenarios when BAO data are included, showing a lower $χ^2_{\min}$ than $Λ$CDM and comparable support according to the AIC criterion. However, the BIC criterion continues to favor the minimal $Λ$CDM model because of the larger parameter space of the extended models. These results suggest that teleparallel cubic Galileon cosmologies remain phenomenologically viable, while a stronger claim regarding the Hubble tension requires further consistency tests.

gr-qc↗

arXiv2026

Spherically-symmetrical vacuum solution in Freund-Nambu scalar-tensor gravity

Scalar--tensor theories of gravity provide a natural extension of general relativity and may predict naked singularities as alternative compact objects. In this work, we investigate a novel exact solution within the Freud--Nambu scalar--tensor gravity framework, generalizing the Janis--Newman--Winicour (JNW) naked singularity spacetime through the introduction of a parameter $q$ coupled to a real scalar field $φ$ with mass $μ$. Although the metric remains identical to the JNW solution, the scalar field profile is modified, providing a parametrized deformation of this class of spacetimes. We analyze particle dynamics in this background, including a direct linear coupling between the test particle and the scalar field characterized by the parameter $g_s$. The influence of these parameters on astrophysical observables is studied through the specific angular momentum, the innermost stable circular orbit (ISCO), and the radiative efficiency of accretion. We also derive the epicyclic frequencies governing oscillatory motion and explore their implications for quasi-periodic oscillations (QPOs) in black hole binaries. Within the epicyclic resonance model, the upper and lower QPO frequencies depend sensitively on the parameters $n$, $g_s$, and $q$. To constrain the model, we perform a Markov Chain Monte Carlo analysis using twin-peak QPO data from the microquasars XTE~J1550--564 and GRS~1915+105. The resulting black hole masses agree with previous estimates and provide the first observational constraints on the parameters $q$ and $g_s$, indicating that modified gravity effects may leave detectable imprints on strong-field astrophysical phenomena.

gr-qc↗

arXiv2026

Effect of gravitational lensing around black hole in dark matter halo in the presence of plasma

This article is devoted to the investigation of the observational properties of the Schwarzschild black hole (BH) surrounded by a dark matter (DM) halo. Our study commences with a brief review of spacetime, including the horizon structure and curvature invariants, which are the Ricci scalar, the square of the Ricci tensor, and the Kretschmann scalar. Subsequently, we explore the massive and massless particle dynamics around the Schwarzschild BH surrounded by a dark matter halo, including the innermost stable circular orbit (ISCO) and photon sphere radii. It was found that the radius of the ISCO increases under the influence of the spacetime parameters. Additionally, we investigate the weak gravitational lensing with the assumption that the BH is surrounded by a uniform and non-uniform plasma. Finally, we examine the impact of a plasma on the BH shadow and employ Event Horizon Telescope (EHT) observational data to constrain the BH's parameters.

gr-qc↗

arXiv2024

Long-lived quasinormal modes and asymptotic tails of regular Schwarzschild-like black holes in the presence of a magnetic field

We analyze the evolution of perturbations of a (charged) massive scalar field near a regular Simpson-Visser black hole, allowing for a non-zero external magnetic field. We show that the damping rate of the quasinormal frequencies is strongly suppressed by both the magnetic field and the mass term, with indications that arbitrarily long-lived modes, or quasi-resonances, may exist in the spectrum. In the time domain, the quasinormal ringing transitions into slowly decaying oscillatory tails, which are qualitatively distinct from the massive tails observed in the absence of a magnetic field. For nonzero multipole and azimuthal numbers, the power-law envelope characteristic of cases without a magnetic field transforms into an oscillatory envelope that cannot be easily fitted with a simple analytical formula.

gr-qc↗

arXiv2024

Exploring a Novel Feature of Ellis Spacetime: Insights into Scalar Field Dynamics

We have studied neutral and charged massive particles dynamics in Ellis spacetime in the presence of the external scalar field. Focusing on the circular motion of massive particles, the impact of an external scalar field on the Innermost Stable Circular Orbit (ISCO) position is analyzed, revealing a non-linear relationship with the scalar field parameter. Perturbation techniques are employed to investigate oscillatory motion near stable orbits in the Ellis spacetime, yielding analytical expressions for radial and angular oscillations. The throat of the wormhole has been constrained by comparing theoretical and observational results for fundamental frequencies of particles from quasars. Finally, scalar and gravitational perturbations in the Ellis spacetime have been studied. It is shown that the equation for the scalar profile function is fully independent from the tensor functions, and the solution can be represented in terms of the confluent Heun function. However, it has been shown that equations for the tensor profile functions strongly depend on the scalar profile functions in the Ellis spacetime, and they are reduced to the Regge-Wheeler-Zerilli equation. Finally, numerical solutions to the Regge-Wheeler-Zerilli equation for the radial functions in the Ellis spacetime have been presented.

gr-qc↗

arXiv2024

Influence of scalar field in massive particle motion in JNW spacetime

In this paper, we investigated the motion of massive particles in the presence of scalar and gravitational fields, particularly focusing on the Janis-Newman-Winicour (JNW) naked singularity solution. It is shown that the innermost stable circular orbit (ISCO) radius strongly depends on scalar coupling parameter. Additionally, we explored the radiation reaction effects on particle dynamics, incorporating a reaction term into the motion equations. Numerical simulations indicated minimal impact on particle trajectories from radiation reaction. We also examined the oscillatory motion of particles around compact objects in the JNW spacetime, focusing on radial and vertical oscillations. Our analysis indicated that the scalar field's coupling parameter and the spacetime deformation parameter $n$ significantly alter the fundamental frequencies of these oscillations. Furthermore, we studied quasi-periodic oscillations (QPOs) in X-ray binaries, using the relativistic precession (RP) model to analyze upper and lower frequency relationships. Our results indicated that increasing parameters ($n$ and $g_s$) shifts the frequency ratio of 3:2 QPOs closer to the naked singularity, with $n$ decreasing and $g_s$ increasing both frequencies. Finally, we analyzed QPO data from selected four X-ray binary systems using Markov Chain Monte Carlo (MCMC) analysis to constrain JNW parameters. Our findings provided insights into the mass, coupling and deformation parameter for each system, enhancing our understanding of compact object dynamics in strong gravitational fields.

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