This study presents a novel interpretation of complexity in the formalism of <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi mathvariant='script'>T</mi><mo>)</mo></mrow></math> gravity, where <italic>R</italic> specifies the Ricci scalar, <math altimg='si2.svg'><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub></math> is written as matter Lagrangian that describes characteristics of the matter fields, and <math altimg='si3.svg'><mi mathvariant='script'>T</mi></math> represents the trace of energy-momentum tensor. We commence with the contemplation of the inner sector as a cylindrical configuration having anisotropic matter and linked with the exterior region through a hypersurface. We determine the modified field equations associated with <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi mathvariant='script'>T</mi><mo>)</mo></mrow></math> gravity and assume the preliminarily established relations between the conformal tensor and the intrinsic curvature. We consider the generally employed mathematical expressions for Tolman mass and C-Energy and evaluate their relationship with the conformal tensor. The structural scalars are calculated from orthogonal splitting of Riemann tensor, out of which <italic>Y<inf>TF</inf></italic> is categorized as complexity factor for the inferred fluid composition. It is important to specify that the complexity factor is eradicated in the framework of uniform matter configuration and also in the scenario when anisotropic terms are canceled with each other. Significant results related to the Weyl scalar, Tolman mass, and the complexity factor are derived in <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi mathvariant='script'>T</mi><mo>)</mo></mrow></math> gravity. The vanishing complexity constraint is considered in order to deal with the modified field equations that have extra degrees of freedom and to find particular solutions corresponding to the specific models.

Pakistan

A. Rehman

Azerbaijan

M. Yousaf

Uzbekistan

Bekzod Rahmatov

Javlon Rayimbaev

Munisbek Akhmedov

Complexity evaluation related to the cylindrically symmetric anisotropic matter in <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi mathvariant='script'>L</mi><mi>m</mi></msub><mo>,</mo><mi mathvariant='script'>T</mi><mo>)</mo></mrow></math> theory

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 Padé 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 <italic>&#956;</italic>, while the damping rate decreases, suggesting the existence of quasi-resonances at sufficiently large <italic>&#956;</italic>. 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.

Czechia

Bekir Can Lütfüoğlu

Fayzullo Shayimov

Ikram Davletov

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

We investigate the influence of a scalar field on particle dynamics and electromagnetic phenomena in the spacetime of a gravitational compact object described by the Fisher-Janis-Newman-Winicour (FJNW) solution. The motion of test particles is analyzed using the Hamilton-Jacobi formalism, with particular attention to the innermost stable circular orbit (ISCO). We further explore photon motion and black hole shadows, deriving analytic expressions for the photon sphere radius and critical impact parameter. Applying these results to Event Horizon Telescope (EHT) observations of M87 and Sgr A, we show that the predicted shadow sizes remain consistent with the measured values within the 1 <italic>&#963;</italic> confidence interval, thereby constraining the scalar parameter. In addition, we obtain the analytical solution of Maxwell&#8217;s equations for the vector potential produced by a stationary current loop in the FJNW background. The resulting magnetic field exhibits a uniform structure in the interior region, reminiscent of the Wald solution, while in the exterior region it behaves like a dipolar field. We find that the external magnetic field strength decreases with increasing scalar parameter, in contrast to the tidal charge scenario of relativistic stars.

Bobur Turimov

Sardor Murodov

Khurshida Khaknazarova

Sulton Usanov

Murodbek Vapayev

Zebo Avezmuratova

Magnetic field by current loop in the Janis-Newman-Winicour spacetime

We investigate the astrophysical properties of the rotating Kazakov-Solodukhin (KS) black hole, a quantum-corrected extension of the Schwarzschild solution that removes the central singularity via an effective mass function. Extending the KS solution to the rotating case, we analyze its geodesic structure and explore the influence of the quantum correction parameter on observable quantities. In particular, we study the effective mass profile, the ergoregion, and photon motion, and compute the black hole shadow. Comparing the resulting shadows with the classical Kerr solution, we find that quantum corrections tend to enlarge the shadow radius and alter its shape. Using these theoretical predictions, we further constrain the parameter space of the rotating KS black hole by confronting the shadow properties with Event Horizon Telescope (EHT) observations of M87* and Sgr A*. Our results demonstrate that high-resolution black hole imaging provides a promising avenue for probing semiclassical modifications of general relativity.

Islom Egamberdiev

Otabek Umarov

Shavkat Karshiboev

Yunus Turaev

Astrophysical signatures of rotating Kazakov-Solodukhin black holes: shadows and constraints from EHT observations

In this work, we explore the physical and observational properties of a static, spherically symmetric black hole solution in scalar–tensor–vector gravity (STVG), also known as modified gravity (MOG), in the presence of perfect fluid dark matter (PFDM). We analyze the motion of magnetized and neutral particles, focusing on the effective potential, innermost stable circular orbits (ISCO), and energy extraction efficiency via the Novikov–Thorne accretion model. Our results show that the MOG parameter $$\alpha $$ and the PFDM parameter $$\lambda $$ significantly influence the particle dynamics, stability conditions, and the efficiency of energy extraction. We also investigate thermodynamic quantities such as Hawking temperature, entropy, heat capacity, and Gibbs free energy, and find that PFDM and MOG parameters critically affect the black hole’s thermal stability and phase transitions. Additionally, we study gravitational lensing in uniform and non-uniform plasma environments and compute light deflection angles modified by both MOG and PFDM effects. Finally, we analyze the shadow cast by the black hole and compare it with Event Horizon Telescope (EHT) observations of M87* and Sgr A*, providing constraints on the MOG and PFDM parameters. Our results suggest that while general relativity remains a good approximation, small deviations due to modified gravity and surrounding dark matter effects cannot be ruled out.

Sirojiddin Saydullayev

Isomiddin Nishonov

Muysin Dusaliyev

Obid Xoldorov

Sunnatillo Urinov

Black hole surrounded by perfect fluid dark matter in STV gravity: particle dynamics, thermodynamics, gravitational weak lensing and EHT tests