arXiv subjects

İzzet Sakallı

Publications and source records attributed to İzzet Sakallı.

At least 55 records · Page 3Linked to original sources

arXiv2025

Particle Dynamics and Thermal Properties in Kalb-Ramond ModMax Black Holes: Theoretical Predictions for Observational Tests of Exotic Physics

We present a comprehensive theoretical study of geodesic motion and thermodynamic behavior in Kalb--Ramond (KR) black hole (BH) spacetimes sourced by ModMax electrodynamics. Both neutral and charged test particle dynamics are investigated, highlighting how the Lorentz symmetry breaking (LSB) parameter $\ell$, the ModMax nonlinearity parameter $γ$, and the discrete branch parameter $ζ$ significantly modify orbital structures compared to classical Schwarzschild and Reissner--Nordström (RN) solutions. Effective potential analysis reveals notable shifts in the innermost stable circular orbit (ISCO): ordinary branches allow stable orbits closer to the horizon, while phantom branches shift them outward by factors of 5--10. For charged particles, the combined influence of modified gravity and nonlinear electromagnetic fields may induce chaotic trajectories in certain regimes. On the thermodynamic side, we derive full expressions for Hawking temperature, entropy, and Helmholtz free energy. Ordinary branches exhibit divergent specific heat indicating second-order phase transitions, whereas phantom branches yield consistently negative specific heat, implying thermal instability. Phantom BHs are found to possess higher Hawking temperatures and show distinct thermodynamic phase structures, including Hawking--Page-type transitions. Observational features such as BH shadows and gravitational lensing are explored, revealing parameter-dependent changes in photon sphere radii and deflection angles. Notably, the deflection angle analysis via the Gauss--Bonnet theorem method (GBTm) shows opposite-sign electromagnetic corrections for phantom versus ordinary branches, suggesting potential observational discriminants.

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arXiv2025

Photon Deflection and Magnification in Kalb-Ramond Black Holes with Topological String Configurations

This theoretical investigation examines gravitational lensing phenomena in Schwarzschild-like black holes (BHs) within Kalb-Ramond (KR) gravity frameworks incorporating cosmic string (CS) and cloud of strings (CoS) topological configurations. We develop comprehensive analytical methodologies for investigating photon deflection angles and magnification characteristics in both Schwarzschild-like BHs in KR gravity pierced by CSs (SKRCS) and Schwarzschild-like BHs in KR gravity with CoS (SKRCoS) spacetime geometries through dual approaches: perturbative expansions yielding approximate solutions and exact elliptic integral formulations providing complete mathematical descriptions across parameter spaces. For CS configurations characterized by Lorentz violation (LV) and CS parameters, deflection angles exhibit systematic modifications through composite geometric factors, while CoS geometries demonstrate distinct deflection characteristics incorporating additional topological parameters that fundamentally alter light propagation dynamics. Magnification analysis reveals distinctive critical curve positioning modifications and amplitude scaling relationships enabling observational discrimination between exotic BH scenarios and conventional spacetime geometries. Strong field analysis utilizing established mathematical frameworks establishes logarithmic divergence coefficients characterizing fundamental scaling behavior in photon sphere proximity regimes. Observational constraints from Solar System precision tests restrict LV parameters within stringent bounds, while galactic-scale observations permit expanded parameter ranges for CS and CoS configurations.

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arXiv2025

Geodesics, Scalar Fields, and GUP-Corrected Thermodynamics of Charged BTZ-like Black Holes in Bopp-Podolsky Electrodynamics

In Ref. [1], the spacetime geometry generated by compact objects in $(2+1)$-dimensional Bopp-Podolsky electrodynamics is derived. Using a perturbative approach, the authors derived a charged BTZ-like black hole solution and computed corrections up to second order in a perturbative expansion valid far from the horizon. In this work, we investigate the same circularly symmetric three-dimensional charged BH solution pierced by disclinations. We begin by analyzing the motion of photons within this spacetime, focusing on how the geometric parameters influence the effective potential governing null geodesic motion. The corresponding equations of motion are derived, and the resulting orbital dynamics are explored through graphical methods to show the influence of key parameters including the BH mass $M$, electric charge $Q$, cosmological constant $Λ$, and BP coupling parameter $b^2$. Extending our analysis to wave dynamics, we examine the propagation of massless scalar fields in the BH solution by solving the Klein-Gordon equation. Through suitable coordinate transformations, we derive a Schrödinger-like equation with an effective potential that encodes the influence of the topological defect and electromagnetic corrections. Additionally, we investigate quantum gravitational effects by applying the Generalized Uncertainty Principle (GUP) to derive a GUP-corrected Hawking temperature, revealing systematic suppression of thermal radiation that could lead to stable BH remnants. Finally, we compute Keplerian frequencies for circular orbits, demonstrating how the interplay between charge, nonlinear electrodynamics, and disclination parameters creates distinctive observational signatures that could potentially test modified gravity theories in strong-field regimes.

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arXiv2025

Regular Magnetically Charged Black Holes from Nonlinear Electrodynamics: Thermodynamics, Light Deflection, and Orbital Dynamics

We investigate the thermodynamic properties, light deflection, and orbital dynamics of regular magnetically charged black holes (NRCBHs) arising from nonlinear electrodynamics (NED) coupled to general relativity. The metric function $f(r)$ ensures complete regularity at the origin while maintaining asymptotic flatness, with the extremal magnetic charge limit reaching $q_{\text{ext}} \approx 2.54M$, significantly exceeding the Reissner-Nordström value. Using the quantum tunneling framework, we derive the Hawking temperature and incorporate generalized uncertainty principle (GUP) corrections, showing $T_{\text{GUP}} = (f'(r_h)/4π)\sqrt{1-2βm_p^2}$. The weak deflection of light is analyzed through the Gauss-Bonnet theorem (GBT), revealing charge-dependent behavior where large $q$ values lead to negative deflection angles due to electromagnetic repulsion. Plasma effects further modify the deflection through the refractive index $n(r) = \sqrt{1 - ω_p^2(r)f(r)/ω_0^2}$. Keplerian motion analysis demonstrates that the angular velocity $Ω(r)$ exhibits charge-sensitive maxima related to quasi-periodic oscillations (QPOs) in accretion disks. Finally, we examine Joule-Thomson expansion (JTE) properties, finding that the coefficient $μ_J$ indicates cooling behavior for higher charges and larger event horizons. Our results provide comprehensive insights into the observational signatures of NRCBHs, with implications for gravitational lensing, X-ray astronomy, and tests of nonlinear electromagnetic theories in strong gravitational fields.

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arXiv2025

Observable signatures of Black Holes with Hernquist Dark Matter Halo having a cloud of strings: From Geodesics to Shadow

We present a comprehensive theoretical investigation of a novel black hole (BH) spacetime: a Schwarzschild BH embedded in a Hernquist-type dark matter halo (HDMH) and surrounded by a cloud of cosmic strings (CSs) -- collectively termed the Schwarzschild-HDMH with CS (SHDMHCS) configuration. By analyzing the spacetime geometry, we explore how key parameters -- the core radius and halo density of the dark matter, along with the string tension -- affect the geodesic motion of both massless and massive particles. Our results reveal that the combined influence of HDMH and CSs modifies the effective potentials for null and timelike geodesics, leading to distinct dynamical behavior compared to standard Schwarzschild geometry. We perform a perturbative analysis for scalar (spin-0), electromagnetic (spin-1), and Dirac (spin-1/2) fields, deriving the associated effective potentials and showing how both the dark halo and CSs alter field propagation and potential barriers. The shadow of the BH is studied in detail: we derive analytical expressions for photon sphere and shadow radii, finding that CSs tend to enlarge the shadow, while HDMH properties tend to shrink it. The combined effects of these parameters significantly influence the shadow's shape and size, producing potentially observable signatures. Our results establish that the SHDMHCS configuration yields distinct observational imprints detectable by present and forthcoming astrophysical instruments. This framework provides new tools for probing exotic matter distributions via gravitational wave observations, orbital dynamics, and high-resolution black hole imaging, offering a pathway to distinguish such configurations from simpler BH models in realistic environments.

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arXiv2025

The effect of pressure anisotropy on quark stars structure in the Starobinsky model

The structure and stability of quark stars (QSs) made of interacting quark matter are discussed in this study, taking color superconductivity and perturbative QCD corrections into account. By combining this EoS with the Tolman-Oppenheimer-Volkoff (TOV) equations, we explore the mass-radius ($M-R$) relations of QSs. The analysis is conducted within the framework of $R^2$ gravity, where the gravity model is described by $f(R) = R + a R^2$. Our primary goal is to investigate how variations in the $R^2$ gravity parameter $a$ affect the mass-radius and mass-central density ($M-ρ_c$) relationships of QSs. Furthermore, we study the dynamical stability of these stars by analyzing the impact of anisotropy parameters $β$ and the interaction parameter $λ$ derived from the EoS, on their stability. Our results demonstrate that the presence of pressure anisotropy plays a significant role in increasing the maximum mass of QSs, with potential implications for the existence of super-massive pulsars. These findings are in agreement with recent astronomical observations, which suggest the possibility of neutron stars exceeding $2M_{\odot}$.

hep-th↗

arXiv2025

Fingerprints of Loop Quantum Gravity Black Holes with Quintessence Field

In this study, we investigate a static, spherically symmetric black hole (BH) within the framework of Loop Quantum Gravity (LQG) surrounded by quintessence field. Our comprehensive analysis shows that the interplay between quantum corrections and exotic matter produces unique spacetime features, most notably a triple-horizon structure for specific parameter combinations. We derive the metric function incorporating both LQG parameters ($α$, $B$) and quintessence parameters ($c$, $w$), analyzing its implications for horizon structure through embedding diagrams. We examine null and timelike geodesics, calculating photon spheres, effective potentials, and orbital dynamics. Our study demonstrates how quantum and quintessence parameters affect BH shadow size and shape, offering potential observational signatures. Through scalar perturbation analysis, we compute quasinormal modes (QNMs) frequencies, confirming the stability of these hybrid BHs while identifying distinctive spectral characteristics. Finally, using the Gauss-Bonnet (GB) theorem modified approach, we derive an analytical expression for gravitational deflection angles, showing a hierarchical structure of contributions from classical, quintessence, and quantum effects at different distance scales.

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arXiv2025

Geodesics and scalar perturbations of deformed AdS-Schwarzschild black hole with a global monopole surrounded by a quintessence field

We conduct a comprehensive investigation of a deformed AdS-Schwarzschild black hole with a global monopole surrounded by a quintessence field. Our analysis focuses on the geodesic motion of both null and timelike particles, enabling precise determination of the photon sphere and quantification of forces acting on photon particles. We systematically examine how the deformation parameter, control parameter, global monopole parameter, and quintessence field parameter influence the energy, angular momentum, and angular velocities of test particles in circular orbits within the equatorial plane. Additionally, we derive and analyze the perturbative potentials for scalar and electromagnetic fields, demonstrating how these parameters modify their structural profiles. Through time-domain integration, we explore the evolution of scalar and electromagnetic perturbations, revealing distinct phases of transient behavior and quasinormal ringing. Finally, we investigate the emission rates of this black hole, establishing connections between its shadow radius and thermal characteristics. Our findings reveal that the global monopole parameter, deformation parameter and quintessence field enhance black hole stability by reducing emission rates, while the control parameter, which helps avoid central singularities, accelerates evaporation by increasing emission.

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arXiv2025

Magnetized Letelier black hole in AdS spacetime

In this study, we investigate the motion of charged, neutral, and light-like particles in a magnetized black hole solution surrounded by a cloud of strings in an anti-de Sitter (AdS) background. This spacetime admits several well-known solutions as special cases, including the Letelier-AdS black hole, the Melvin spacetime, and the Schwarzschild-AdS black hole. We demonstrate that key parameters characterizing the geometry-such as the cloud of strings parameter, the magnetic field strength, and the AdS radius-significantly affect the trajectories of these particles. Our analysis shows that increasing the cloud of strings parameter weakens the gravitational influence, while the magnetic field introduces additional attractive components that can destabilize particle orbits. We examine the photon sphere and calculate the black hole shadow, showing that the shadow radius decreases with increasing magnetic field parameter but increases with the cloud of strings parameter. These findings provide potential observables for distinguishing between different black hole models in realistic astrophysical environments.

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arXiv2025

White dwarfs in regularized 4D Einstein-Gauss-Bonnet gravity

White dwarfs (WDs), as the remnants of low to intermediate-mass stars, provide a unique opportunity to explore the interplay between quantum mechanical degeneracy pressure and gravitational forces under extreme conditions. In this study, we examine the structure and macroscopic properties of WDs within the framework of 4D Einstein-Gauss-Bonnet (4DEGB) gravity, a modified theory that incorporates higher-order curvature corrections through the Gauss-Bonnet coupling constant $α$. Using the modified Tolman-Oppenheimer-Volkoff (TOV) equations tailored for 4DEGB gravity, we analyze the hydrostatic equilibrium of WDs modeled with a realistic equation of state (EoS). Our findings reveal that the inclusion of the Gauss-Bonnet (GB) term significantly influences the mass-radius ($M-R$) relation, allowing for deviations from the Chandrasekhar mass limit. In particular, we observe that such stars become more compact and slightly smaller with the increase of the parameter $α$. For WDs with $\vertα\vert \leq 500\, \rm km^2$, the impact of 4DEGB gravity appears to be negligible. However, a larger range for $α$ allows for appreciable changes in the $M-R$ diagram, mainly in the high-central-density region. Furthermore, we explore the role of anisotropic pressures, quantified by the parameter $β$, on such systems and demonstrate their impact on stability and compactness. For sufficiently large values of $\vertβ\vert$ keeping negative $β$ with a large and positive $α$, there exists a second stable branch according to the classical stability criterion $dM/dρ_c >0$. These results suggest that anisotropic WDs in 4DEGB gravity exhibit unique characteristics that distinguish them from their general relativistic counterparts, offering a novel testing ground for modified gravity theories in astrophysical settings.

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arXiv2025

Geometric and Thermodynamic Properties of Frolov Black Holes with Topological Defects

We investigated a modified Frolov black hole (BH) model that incorporates both a global monopole (GM) and a cosmic string (CS) to explore the interplay between non-singular BH regularization and topological defect effects. In our study, we derived a spacetime metric characterized by a regulated core through a length scale parameter $α$ and introduced additional modifications via the GM parameter $η$ and the CS parameter $a$, which collectively alter the horizon structure and causal geometry of the BH. We analyzed the thermodynamic properties by deriving expressions for the mass function, Hawking temperature, and entropy, and found that the inclusion of GM and CS significantly deviates the BH entropy from the conventional Bekenstein-Hawking area law, while numerical investigations showed that the shadow radius exhibits contrasting behaviors: the Frolov parameters tend to reduce the shadow size whereas the topological defects enhance it. Furthermore, we examined the dynamics of scalar and electromagnetic perturbations by solving the massless Klein-Gordon equation in the BH background and computed the quasinormal modes (QNMs) using the WKB approximation, which confirmed the BH's stability and revealed that the oscillation frequencies and damping rates are strongly dependent on the parameters $α$, $q$, $η$, and $a$. Our results suggest that the distinct observational signatures arising from this composite BH model may provide a promising avenue for testing modified gravity theories in the strong-field regime.

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arXiv2025

Gravitational Lensing Phenomena of Ellis-Bronnikov-Morris-Thorne Wormhole with Global Monopole and Cosmic String

In this paper, we theoretically investigate gravitational lensing within the space-time framework of traversable wormholes, focusing on the combined effects of a global monopole and a cosmic string. Specifically, we examine the Ellis-Bronnikov-Morris-Thorne wormhole metric and analyze how these topological defects influence photon trajectories. By considering the weak-field limit, we derive analytical expressions for the photon deflection angle, highlighting how factors such as the wormhole throat radius, the global monopole charge, and the cosmic string influence the gravitational lensing phenomenon. We also examine the weak-field limit of lensing phenomena for a zero wormhole throat radius and derive an analytical expression for the deflection angle of photon light in this scenario.

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arXiv2025

Reconciling the Weak Gravity and Weak Cosmic Censorship Conjectures in Einstein-Euler-Heisenberg-AdS Black Holes

The potential conflict between the Weak Gravity Conjecture (WGC) and the Weak Cosmic Censorship Conjecture (WCCC) poses a significant challenge in general relativity. The WCCC serves as a fundamental assumption ensuring the coherence of gravitational theory. This study investigates the reconciliation of the WGC and the WCCC by examining Einstein-Euler-Heisenberg-AdS black holes in four-dimensional spacetime. By imposing specific constraints on the metric parameters, we demonstrate that the WGC and the WCCC can coexist harmoniously. Detailed analyses of Einstein-Euler-Heisenberg-AdS black holes for $ Q > M $ validate the simultaneous fulfillment of the two conjectures, particularly in scenarios where $ q^2/m^2 \geq \left(Q^2 / M^2\right)_{\text{e}} $. The electromagnetic self-interaction parameter $ μ$ plays a crucial role in achieving this compatibility. Our findings establish that Einstein-Euler-Heisenberg-AdS black holes provide a robust framework for harmonizing the WGC and the WCCC. In particular, for exceedingly small values of ($μ$)-or, equivalently, when the condition ($μ\ll \ell$) is satisfied-the structure of our black hole transitions in a way that distinctly reveals its compatibility with the WGC. This study also explores the compatibility of the WGC and the WCCC with photon spheres. It examines parameter spaces that satisfy both conjectures, ensuring event horizons and photon spheres while maintaining black hole properties. Key results demonstrate that small $ μ$ values preserve WCCC adherence and validate WGC through photon sphere characteristics.

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arXiv2025

Lorentz Symmetry Violation in Charged Black Hole Thermodynamics and Gravitational Lensing: Effects of the Kalb-Ramond Field

This study investigates the consequences of Lorentz symmetry violation in the thermodynamics and gravitational lensing of charged black holes coupled to the Kalb-Ramond field. We first explore the impact of Lorentz-violating parameters on key thermodynamic properties, including the Hawking temperature, entropy, and specific heat, demonstrating significant deviations from their Lorentz-symmetric counterparts. Our analysis reveals that the Lorentz-violating parameter b induces modifications in phase transitions and stability conditions, offering novel insights into black hole thermodynamics. Additionally, the influence of Lorentz symmetry breaking on gravitational lensing is examined using modifications to the Rindler-Ishak method, showing that these effects enhance the bending of light near compact objects. Our findings, derived within the framework of the standard model extension and bumblebee gravity models, suggest that Lorentz-violating corrections could lead to observable astrophysical phenomena, providing potential tests for deviations from Einstein's theory of relativity.

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arXiv2025

Ayón-Beato-García black hole in AdS space-time surrounded by quintessence: geodesic, shadow and thermodynamics

In this study, we present a novel exact solution to the gravitational field equations, known as the Ayón-Beato-García black hole solution, set against the backdrop of anti-de Sitter space and surrounded by a quintessence field. This solution serves as an interpolation between three distinct anti-de Sitter black hole configurations, namely, the Ayón-Beato-García, Schwarzschild-Kiselev, and the standard Schwarzschild black hole solutions. The first aspect of our investigation focuses on the geodesic motion of particles, where we explore how the black hole's space-time geometry-incorporating the effects of nonlinear electrodynamics, the quintessence field, and the curvature radius-influences the dynamics of both massless and massive particles near the black hole. To further enrich our analysis, we extend the study to include the perturbative dynamics of a massless scalar field within the black hole solution, placing special emphasis on the scalar perturbative potential. Subsequently, we focus into the phenomenon of black hole shadows, examining how various parameters, such as the nonlinear electrodynamics, the curvature of space-time and the presence of the quintessence field, impact the size and shape of the shadow cast by the black hole. In the final segment of our study, we shift our attention to the thermodynamics of the black hole solution. We compute several essential thermodynamic quantities, including the Hawking temperature, specific heat capacity, and Gibbs free energy, analyzing how these properties evolve in response to changes in the various parameters that define the space-time geometry, which in turn affect the gravitational field when compared to the traditional black hole

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arXiv2025

Motions of Test Particles in Gravitational Field, Perturbations and Greybody Factor of Bardeen-like AdS Black Hole with Phantom Global Monopoles

We investigate the dynamics of test particles, perturbations, and greybody factors within the framework of a Bardeen-like AdS black hole (BH) with a phantom global monopole. This study explores the interactions between nonlinear electrodynamics, the energy scale of symmetry breaking, and space-time topology. We analyze the geodesic motion of null and time-like particles, deriving effective potentials that describe their trajectories. Utilizing the Regge-Wheeler potential, we calculate the quasinormal modes (QNMs) for scalar, vector, and tensor perturbations, applying the sixth-order WKB approximation. Our findings highlight how the Bardeen-like parameter ($\mathrm{b}$) and the energy scale of symmetry breaking, characterized by the parameter ($η$), influence the QNM spectra, with potential implications for gravitational wave observations. We also examine greybody factors, focusing on the transmission and reflection coefficients for scalar and axial fields, and employ semi-analytic techniques to derive precise bounds. Furthermore, we assess the thermodynamic stability of the BH, emphasizing the role of these parameters in phase transitions and stability criteria.

hep-th↗

arXiv2025

Shadow properties and orbital dynamics around an effective quantum-modified black hole surrounded by quintessential dark energy

In this study, we investigate black holes (BHs) surrounded by a quintessence field (QF) within the framework of effective quantum gravity (EQG). We analyze the spacetime metric characterized by quantum correction parameter $ξ$ and quintessence parameters $(c,w)$, revealing a rich three-horizon structure whose properties depend on both quantum effects and dark energy. Our main focus is on understanding the observational signatures and dynamical behavior of these modified BHs. We derive analytical expressions for the photon sphere and shadow radius for various values of the state parameter, finding that quintessence fields increase the shadow radius while quantum corrections decrease it-a distinctive interplay that creates potentially observable effects. Using Event Horizon Telescope data from M87*, we establish constraints on the quantum correction parameter, showing that the allowable range for $ξ$ increases with the quintessence parameter $c$. We conduct a comprehensive analysis of null and timelike geodesics, demonstrating how quantum corrections enhance interactions between photons and the gravitational field while modifying the energy, angular momentum, and stability properties of massive particle orbits. Our investigation extends to periodic orbits characterized by zoom-whirl behavior, finding that quintessence allows such orbits to occur at lower energies compared to purely quantum-corrected BHs. We further analyze scalar perturbations and their effective potentials, which reveal how both quantum and quintessence effects shape the response characteristics of these BHs. Throughout our study, we find that quantum corrections and quintessence frequently produce counteracting effects on observables that could provide simultaneous tests of quantum gravity theories and dark energy models through future high-precision astronomical observations.

gr-qc↗

arXiv2025

Photon spheres, gravitational lensing/mirroring, and greybody radiation in deformed AdS-Schwarzschild black holes with phantom global monopole

In this study, we investigate the geodesic structure, gravitational lensing/mirroring phenomena, and scalar perturbations of deformed AdS-Schwarzschild black holes with global monopoles, incorporating both ordinary and phantom configurations. We introduce a modified black hole metric characterized by a deformation parameter $α$, a control parameter $β$, and a symmetry-breaking scale parameter $η$, which collectively influence the spacetime geometry. Through comprehensive geodesic analysis, we determine the photon sphere radius numerically for various parameter configurations, revealing significant differences between ordinary and phantom global monopoles. The stability of timelike circular orbits is assessed via the Lyapunov exponent, demonstrating how these parameters affect orbital dynamics. Our gravitational lensing analysis, employing the Gauss-Bonnet theorem, reveals a remarkable gravitational mirroring effect in phantom monopole spacetimes at high AdS curvature radii, where light rays experience negative deflection angles-being repelled rather than attracted by the gravitational field. Furthermore, we analyze massless scalar perturbations and derive the corresponding greybody factors, which characterize the transmission of Hawking radiation through the effective potential barrier surrounding the black hole. Our numerical results indicate that phantom global monopoles substantially modify both gravitational lensing/mirroring properties and the radiation spectrum compared to ordinary monopoles. The presence of the deformation parameter $α$ introduces additional complexity to the system, leading to distinct thermodynamic behavior that deviates significantly from the standard AdS-Schwarzschild solution.

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