arXiv subjects

Özcan Sert

Publications and source records attributed to Özcan Sert.

At least 19 recordsLinked to original sources

arXiv2026

Black Hole Solutions with Scalar Fields and Anisotropic Matter in Non-Minimal $Y(R)F^2$ Gravity

We investigate exact spherically symmetric and static black hole solutions in a non-minimally coupled Einstein--Maxwell theory of the $Y(R)F^2$ type, extended by a minimally coupled real scalar field and an anisotropic matter distribution. The Maxwell field is coupled to the spacetime curvature through an arbitrary function of the Ricci scalar, while the scalar field is described by a kinetic term and a scalar potential. We obtain exact solutions for power-law and logarithmic forms of the non-minimal coupling function and analyze the corresponding spacetime geometries. In particular, we identify a special $β=-1/3$ case for which the general power-law solution becomes singular and derive a new logarithmic metric by solving the field equations independently. The resulting configurations are asymptotically flat and exhibit modified gravitational properties associated with the interplay between the scalar field, anisotropic matter, and non-minimal electromagnetic coupling. We further show that the magnetic solutions admit electrically charged counterparts through an electromagnetic duality transformation, under which the metric and scalar sector remain invariant while the non-minimal coupling function is inverted. The obtained solutions provide a useful framework for investigating black hole horizons, thermodynamic properties, geodesic motion, and astrophysical phenomena such as galactic rotation curves in curvature-dependent electromagnetic theories.

gr-qc↗

arXiv2026

Quantum-Corrected Thermodynamics, Dirac Perturbations, Geodesic Structure, and Topological Phases of Black Holes with Non-Minimal Logarithmic Coupling

We study the thermodynamic and dynamical properties of static, spherically symmetric BHs in Einstein-Maxwell theory modified by a non-minimal $\ln(R)F^{2}$ coupling. The Hawking temperature follows from the Hamilton-Jacobi form of the fermionic tunnelling method for spin-$\tfrac12$ particles, and it carries scale-dependent logarithmic corrections. We then analyze the propagation of massless Dirac fields, compute the quasinormal-mode (QNM) spectrum with the third-order WKB approximation, and read off a quality factor whose balance between oscillation and damping depends on the logarithmic coupling in a mode-dependent way. Moving outward from the horizon, we work out the transmission of the fermionic field and its Hawking emission, and we solve the null and timelike geodesic problems to obtain the photon sphere, the shadow radius, the innermost stable circular orbit (ISCO), the associated zoom-whirl bound orbits, and the orbital and epicyclic frequencies that set the twin-peak quasiperiodic-oscillation (QPO) ratio. A photon-sphere reading of the eikonal QNM frequencies ties the geodesic sector back to the field perturbations. On the thermodynamic side, we build the phase space with quantum-geometric corrections through the Barrow entropy, and we characterize the global phase structure with the topological method, where the winding numbers of the off-shell free energy are governed by the interplay of the fractal Barrow deformation, the electric charge, and the logarithmic coupling. We find that the effective pressure vanishes exactly on the topological defect line, which links the pressure sign to the local stability of each branch.

gr-qc↗

arXiv2025

Quantum-Corrected Thermodynamics and Plasma Lensing in Non-Minimally Coupled Symmetric Teleparallel Black Holes

We investigate the thermodynamic and optical signatures of electrically charged black holes (BHs) in symmetric teleparallel gravity (STPG) with non-minimal electromagnetic coupling, incorporating quantum corrections and plasma dispersion effects. The BH solution, characterized by a coupling parameter $k$, generalizes the Reissner-Nordström spacetime through power-law modifications to electromagnetic terms in the metric function. We implement exponential corrections to the Bekenstein-Hawking entropy of the form $S = S_0 + e^{-S_0}$ and derive quantum-corrected expressions for fundamental thermodynamic quantities including internal energy, Helmholtz and Gibbs free energies, pressure, enthalpy, and heat capacity. Our analysis reveals rich phase transition structures with second-order transitions occurring at critical horizon radii for specific coupling values, demonstrating enhanced thermodynamic instability under strong non-minimal coupling effects. The quantum-corrected Joule-Thomson expansion analysis identifies distinct cooling and heating regimes separated by inversion points that shift systematically with the coupling parameter $k$. We analyze the efficiency of heat engines operating in Carnot cycles, finding that electromagnetic charge enhances thermodynamic performance with efficiency values approaching 99\% for optimal configurations in this geometry. Using the Gauss-Bonnet theorem, we derive analytical expressions for gravitational deflection angles in both vacuum and plasma environments, revealing how non-minimal coupling and plasma dispersion create frequency-dependent lensing signatures that differ substantially from general relativity predictions.

gr-qc↗

arXiv2024

Wormholes in the Non-minimally Coupled Gravity with Electromagnetism

Since the general relativistic approach requires exotic matter with negative energy density, constructing wormholes containing realistic matter is a crucial challenge. Therefore, extending General Relativity to non-minimal cases may be an alternative option. In this paper, we investigate wormholes which are supported by the non-minimally coupled electromagnetic fields to gravity in $Y(R)F^2$ form where $F^2$ is the Maxwell invariant and $Y(R)$ is a function of the Ricci scalar $R$. We consider both electrically and magnetically charged cases. Then we give some exact asymptotically AdS/dS and flat solutions for traversable wormhole geometries. By discussing whether these obtained geometries satisfy the energy conditions and vanishing sound speed condition, we determine stable solutions containing realistic matter for some parameter values.

gr-qc↗

arXiv2023

The non-minimally coupled symmetric teleparallel gravity with electromagnetic field

We construct a symmetric teleparallel gravity model which is non-minimally coupled with electromagnetic field in four dimensions inspired by its Riemannian equivalent. We derive the field equations by taking the variation of this model, which is written here for the first time. Then, we find some classes of spherically symmetric static solutions by the coincident gauge of symmetric teleparallel spacetime.

gr-qc↗

arXiv2021

Gravastars in a Non-minimally Coupled Gravity with Electromagnetism

In this paper we investigate the gravitational vacuum stars which called gravastars in the non-minimally coupled models with electromagnetic and gravitational fields. We consider two non-minimal models and find the corresponding spherically symmetric exact solutions in the interior of the star consisting of the dark energy condensate. Our models turn out to be Einstein-Maxwell model at the outside of the star and the solutions become the Reissner-Nordstr{ö}m solution. The physical quantities of these models are continuous and non-singular in some range of parameters and the exterior geometry continuously matches with the interior geometry at the surface. We calculate the matter mass, the total gravitational mass, the electric charge and redshift of the star for the two models. We notice that these quantities except redshift are dependent of a subtle free parameter, $k$, of the model. We also remark a wide redshift range from zero to infinity depending on one free parameter, $β$, in the second model.

gr-qc↗

arXiv2020

Noether Symmetry Approach to the Non-Minimally Coupled $Y(R)F^2$ Gravity

We use Noether symmetry approach to find spherically symmetric static solutions of the non-minimally coupled electromagnetic fields to gravity. We construct the point-like Lagrangian under the spherical symmetry assumption. Then we determine Noether symmetry and the corresponding conserved charge. We derive Euler-Lagrange equations from this point-like Lagrangian and show that these equations are same with the differential equations derived from the field equations of the model. Also we give two new exact asymptotically flat solutions to these equations and investigate some thermodynamic properties of these black holes.

gr-qc↗

arXiv2019

Inflation of the Universe by the Non-minimal $Y(R)F^2$ Models

The cosmological solutions of the non-minimal $ Y (R)F^2 $ theory which are compatible with FRW space-time are investigated. In order to avoid the isotropy violation of a vector field, it can be considered that the presence of a triplet of vector fields satisfying $SO(3)$ symmetry, or the average of randomly oriented electromagnetic fields over the sufficiently large volume. By considering the symmetry arguments, the inflation driven by the non-minimally coupled vector fields is studied. Then the cosmological solutions and corresponding models are obtained with the power law, hyperbolic and hybrid scale functions.

gr-qc↗

arXiv2019

Anisotropic cosmological solutions to the $Y(R)F^2$ gravity

We investigate anisotropic cosmological solutions of the theory with non-minimal couplings between electromagnetic fields and gravity in $Y(R) F^2$ form. After we derive the field equations by the variational principle, we look for spatially flat cosmological solutions with magnetic fields or electric fields. Then we give exact anisotropic solutions by assuming the hyperbolic expansion functions. We observe that the solutions approach to the isotropic case in late-times.

gr-qc↗

arXiv2018

Anisotropic Stars in the Non-minimal $Y(R)F^2$ Gravity

We investigate anisotropic compact stars in the non-minimal $Y(R)F^2$ model of gravity which couples an arbitrary function of curvature scalar $Y(R)$ to the electromagnetic field invariant $F^2$. After we obtain exact anisotropic solutions to the field equations of the model, we apply the continuity conditions to the solutions at the boundary of the star. Then we find the mass, electric charge, and surface gravitational redshift by the parameters of the model and radius of the star.

gr-qc↗

arXiv2018

Compact Stars in the Non-minimally Coupled Electromagnetic Fields to Gravity

We investigate the gravitational models with the non-minimal $Y(R)F^2$ coupled electromagnetic fields to gravity, in order to describe charged compact stars, where $Y(R) $ denotes a function of the Ricci curvature scalar $R$ and $F^2$ denotes the Maxwell invariant term. We determine two parameter family of exact spherically symmetric static solutions and the corresponding non-minimal model without assuming any relation between energy density of matter and pressure. We give the mass-radius, electric charge-radius ratios and surface gravitational redshift which are obtained by the boundary conditions. We reach a wide range of possibilities for the parameters $k$ and $α$ in these solutions. Lastly we show that the models can describe the compact stars even in the the more simple case $α=3$.

gr-qc↗

arXiv2017

Radiation Fluid Stars in the Non-minimally Coupled $Y(R)F^2$ Gravity

We propose a non-minimally coupled gravity model in $ Y(R)F^2 $ form to describe the radiation fluid stars which have the radiative equation of state between the energy density $ ρ$ and the pressure $p$ as $ρ=3p $. Here $F^2$ is the Maxwell invariant and $Y(R)$ is a function of the Ricci scalar $R$. We give the gravitational and electromagnetic field equations in differential form notation taking the infinitesimal variations of the model. We look for electrically charged star solutions to the field equations under a constraint which eliminating complexity of the higher order terms in the field equations. We determine the non-minimally coupled function $Y(R)$ and the corresponding model which admits new exact solutions in the interior of star and Reissner-Nordstrom solution at the exterior region. Using vanishing pressure condition at the boundary together with the continuity conditions of the metric functions and the electric charge, we find the mass-radius ratio, charge-radius ratio and gravitational surface redshift depending on the parameter of the model for the radiation fluid star. We derive general restrictions for the ratios and redshift of the charged compact stars. We obtain a slightly smaller upper mass-radius ratio limit than the Buchdahl bound $ 4/9 $ and a smaller upper redshift limit than the bound of the standard General Relativistic stars.

gr-qc↗

arXiv2016

Holographic Superconductors with the General $RF^2$ type Couplings

We explore the effects of the general non-minimally coupled $RF^2$-type couplings on the holographic s-wave superconductors numerically in the Schwarzschild-AdS background. We calculate the condensation and conductivity of the model for the coupling parameters $a_1$ and $β$. We obtain that the bigger deviations of the parameter $a_1$ from the minimal case lead to the larger deviations of the gap frequency from the universal value $ω_g/T_c \approx 8$. Moreover the smaller $β$ and $a_1$ cause to gradually stronger and narrower coherence peak.

hep-th↗

arXiv2016

Regular Black Hole Solutions of the Non-minimally Coupled $Y(R)F^2$ Gravity

In this study we investigate regular black hole solutions of the non-minimally coupled $ Y(R)F^2 $ gravity model. We give two regular black hole solutions and the corresponding non-minimal model for both electrically or magnetically charged cases. We calculate all the energy conditions for these solutions.

gr-qc↗

arXiv2013

Symmetric Teleparallel Gravity: Some exact solutions and spinor couplings

In this paper we elaborate on the symmetric teleparallel gravity (STPG) written in a non-Riemannian spacetime with nonzero nonmetricity, but zero torsion and zero curvature. Firstly we give a prescription for obtaining the nonmetricity from the metric in a peculiar gauge. Then we state that under a novel prescription of parallel transportation of a tangent vector in this non-Riemannian geometry the autoparallel curves coincides with those of the Riemannian spacetimes. Subsequently we represent the symmetric teleparallel theory of gravity by the most general quadratic and parity conserving lagrangian with lagrange multipliers for vanishing torsion and curvature. We show that our lagrangian is equivalent to the Einstein-Hilbert lagrangian for certain values of coupling coefficients. Thus we arrive at calculating the field equations via independent variations. Then we obtain in turn conformal, spherically symmetric static, cosmological and pp-wave solutions exactly. Finally we discuss a minimal coupling of a spin-1/2 field to STPG.

gr-qc↗

arXiv2013

Non-minimal $RF^2$-type corrections to holographic superconductor

We study $(2+1)$-dimensional holographic superconductors in the presence of non-minimally coupled electromagnetic field to gravity by considering an arbitrary linear combination of $RF^2$-type invariants with three parameters. Our analytical analysis shows that the non-minimal couplings affect the condensate and the critical temperature.

hep-th↗

arXiv2013

Electromagnetic Duality and New Solutions of the Non-minimally Coupled Y(R)-Maxwell Gravity

Non-minimally coupled Y(R)-Maxwell gravity which have some interesting solutions may be used to understand dark matter, dark energy, the origin of cosmic magnetic field and the evaluation of the universe. We give some new solutions to the model such as spherically symmetric electric, magnetic and dyon solutions. We point out an existence of an electromagnetic duality transformation for the model.

gr-qc↗

arXiv2012

Gravity and Electromagnetism with $Y(R)F^2$-type Coupling and Magnetic Monopole Solutions

We investigate $ Y(R) F^2 $-type coupling of electromagnetic fields to gravity. After we derive field equations by a first order variational principle from the Lagrangian formulation of the non-minimally coupled theory, we look for static, spherically symmetric, magnetic monopole solutions. We point out that the solutions can provide possible geometries which may explain the flatness of the observed rotation curves of galaxies.

gr-qc↗