arXiv subjects

Beyhan Puliçe

Publications and source records attributed to Beyhan Puliçe.

11 recordsLinked to original sources

arXiv2026

Black Hole Shadow and Light Deflection in Generalized Heisenberg-Euler Nonlinear Electrodynamics

We study the optical properties of electrically charged black holes sourced by generalized Heisenberg-Euler nonlinear electrodynamics (NLED) in the second-order formalism. Using the exact parametric form of the static spherically symmetric solution, we analyze the photon sphere, the black hole shadow, and the light deflection angle, and compare the results with those of the Reissner-Nordström and Schwarzschild cases. We find that the photon sphere and shadow radii decrease with increasing charge and increase with black hole mass, while NLED effects become significant mainly near extremality. By confronting the dimensionless shadow radius with the Event Horizon Telescope (EHT) bounds from Sgr A* and M87*, we derive phenomenological upper limits on the charge, with Sgr A* providing the stronger constraint. We further show that, for fixed impact parameter and charge, the deflection angle is systematically larger than in the corresponding Reissner-Nordström spacetime, and that the critical impact parameter is shifted to larger values. Our results show that NLED corrections produce observable modifications in the optical properties of charged black holes, especially close to extremality.

gr-qc↗

arXiv2026

Spinning Particle Dynamics and Observational Redshift around an Asymptotically Flat Symmergent Black Hole

We investigate timelike particle dynamics, collision energetics, and photon frequency shifts in the perturbative variable-scalar curvature branch of asymptotically flat symmergent gravity. The low-energy vacuum action contains an $R^{2}$ correction whose coefficient is set by the boson--fermion imbalance of the underlying quantum field theory. At linear order, the exterior geometry is conformal to Schwarzschild spacetime through a radial mode satisfying a linear equation. We retain an independent boundary-condition-dependent amplitude and restrict the analysis to the perturbative domain. The two signs of the symmergent parameter $γ$ yield distinct profiles: $γ>0$ gives a Yukawa-suppressed deformation, whereas $γ<0$ produces an oscillatory inverse-radius deformation. We derive radial equations, effective potentials, circular-orbit and marginal-stability conditions for neutral, electrically charged, and spinning massive particles. Charged particles are treated in the test-field approximation, while spinning particles obey the Mathisson--Papapetrou--Dixon equations with the Tulczyjew condition. We also compute the center-of-mass energy of neutral-particle collisions and the frequency shifts of photons emitted tangentially by circular geodesic sources and detected by a static observer at infinity. The redshift and blueshift factors satisfy $(1+z_{+})(1+z_{-})=1/A(r_e)$, directly linking their product to the lapse function at emission. The $γ>0$ branch yields smooth, short-range deviations from Schwarzschild dynamics, whereas the $γ<0$ branch can generate oscillatory radial bands admitting circular-orbit solutions whose stability must be tested independently. These observables provide complementary probes of the variable-curvature sector, although their quantitative interpretation also depends on the deformation amplitude and, for the oscillatory branch, its phase.

gr-qc↗

arXiv2026

Spinning Particles around Einstein-Geometric Proca AdS Compact Objects

We investigate the dynamics of spinning test particles in the vicinity of Einstein--geometric Proca (EGP) Anti-de Sitter (AdS) compact objects, which arise from metric-Palatini gravity extended by the antisymmetric part of the affine curvature. Using the Mathisson-Papapetrou-Dixon (MPD) equations with the Tulczyjew spin supplementary condition, we derive the effective potential and analyze the equatorial motion of spinning particles. The influence of the model parameters $q_{1}$, $q_{2}$, and the Proca mass parameter $σ$ on the innermost stable circular orbits (ISCO), superluminal spin bounds, and orbital stability is systematically explored. Our results show that increasing $q_{1}$ and $q_{2}$ reduces the ISCO radius, angular momentum, and energy, while spin orientation introduces significant modifications to orbital behavior. We further examine head-on collisions of spinning particles near the horizon and demonstrate how the center-of-mass energy depends on spin and the EGP theory parameters. The study reveals that Einstein-geometric Proca AdS black holes may act as efficient particle accelerators, with distinctive features absent in Schwarzschild or standard AdS backgrounds. These findings provide new insights into the interplay between spin dynamics, modified gravity, and strong-field compact object physics.

gr-qc↗

arXiv2026

The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106, https://www.cost.eu/actions/CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.

hep-ph↗

arXiv2025

Thermodynamics of Einstein-Geometric Proca AdS compact objects

In this study we explore metric-Palatini gravity extended by the antisymmetric component of the affine curvature. This gravitational theory results in general relativity plus a geometric Proca field. Building on our previous work, where we constructed its static spherically symmetric solutions in the Anti-de Sitter (AdS) background (Eur. Phys. J. C 83(4):318, 2023), we conduct a comprehensive analysis of the system's thermodynamics. We examine the thermodynamic properties of the Einstein-Geometric Proca AdS compact objects, focusing on the Hawking temperature, enthalpy, heat capacity, entropy, and Gibbs free energy. Particular attention is given to the dependence of the Hawking temperature, enthalpy, and heat capacity on the uniform potential $q_{1}$ and the electromagnetic-type charge $q_{2}$. Through numerical analysis we compute the entropy and Gibbs free energy and investigate how these quantities vary with the model parameters.

gr-qc↗

arXiv2024

Quasinormal Modes and Greybody Factors of Charged Symmergent Black Hole

In this paper, we investigate quasinormal modes (QNMs) and greybody factors within the framework of Symmergent gravity, an emergent gravity model with an $R + R^2$ curvature sector. Building on our previous work on static spherically-symmetric solutions [Class. Quant. Grav. 40 (2023) 19, 195003], we explore the effects of the key parameters, including the quadratic curvature coupling parameter $c_{\rm O}$ and the vacuum energy parameter $α$. For both scalar and electromagnetic perturbations, an increase in $α$ leads to a nearly linear rise in both oscillation frequencies and damping rates. The other parameter $c_{\rm O}$ affects the QNMs spectrum nonlinearly. Additionally, the charge $Q$ of the black hole introduces nonlinear behavior, where higher charges amplify the black hole's electromagnetic field, resulting in increased oscillation frequencies and faster stabilization. These findings enhance our understanding of charged black hole stability and gravitational wave astrophysics. Further, the analysis of greybody factors reveals that increasing $α$, $c_{\rm O}$, and $Q$ reduces the absorption of radiation, with electromagnetic perturbations reaching maximum absorption at slightly lower frequencies compared to scalar perturbations.

gr-qc↗

arXiv2024

Constraints on Metric-Palatini Gravity from QPO Data

In this work, we study metric-Palatini gravity extended by the antisymmetric part of the affine curvature. This gravity theory leads to general relativity plus a geometric Proca field. Using our previous construction of its static spherically-symmetric AdS solution [Eur. Phys. J. C83 (2023) 4, 318], we perform a detailed analysis in this work using the observational quasiperiodic oscillations (QPOs) data. To this end, we use the latest data from stellar-mass black hole GRO J1655-40, intermediate-mass black hole in M82-X1, and the super-massive black hole in SgA* (our Milky Way) and perform a Monte-Carlo-Markov-Chain (MCMC) analysis to determine or bound the model parameters. Our results shed light on the allowed ranges of the Proca mass and other parameters. The results imply that our solutions can cover all three astrophysical black holes. Our analysis can also be extended to more general metric-affine gravity theories.

gr-qc↗

arXiv2024

Asymptotically-Flat Black Hole Solutions in Symmergent Gravity

Symmergent gravity is an emergent gravity model with an $R+R^2$ curvature sector and an extended particle sector having new particles beyond the known ones. With constant scalar curvature, asymptotically flat black hole solutions are known to have no sensitivity to the quadratic curvature term (coefficient of $R^2$). With variable scalar curvature, however, asymptotically-flat symmergent black hole solutions turn out to explicitly depend on the quadratic curvature term. In the present work, we construct asymptotically-flat symmergent black holes with variable scalar curvature and use its evaporation, shadow, and deflection angle to constrain the symmergent gravity parameters. Concerning their evaporation, we find that the new particles predicted by symmergent gravity, even if they do not interact with the known particles, can enhance the black hole evaporation rate. Concerning their shadow, we show that statistically significant symmergent effects are reached at the $2\,σ$ level for the observational data of the Event Horizon Telescope (EHT) on the Sagittarius A* supermassive black hole. Concerning their weak deflection angle, we reveal discernible features for the boson-fermion number differences, particularly at large impact parameters. These findings hold the potential to serve as theoretical predictions for future observations and investigations on black hole properties.

gr-qc↗

arXiv2023

Constraints on charged Symmergent black hole from shadow and lensing

In this paper, we report on exact charged black hole solutions in symmergent gravity with Maxwell field. Symmergent gravity induces the gravitational constant $G$, quadratic curvature coefficient $c_{\rm O}$, and the vacuum energy $V_{\rm O}$ from the flat spacetime matter loops. In the limit in which all fields are degenerate in mass, the vacuum energy $V_{\rm O}$ can be expressed in terms of $G$ and $c_{\rm O}$. We parametrize deviation from this limit by a parameter ${\hat α}$ such that the black hole spacetime is dS for ${\hat α} < 1$ and AdS for ${\hat α} > 1$. In our analysis, we study horizon formation, shadow cast and gravitational lensing as functions of the black hole charge, and find that there is an upper bound on the charge. At relatively low values of charge, applicable to astronomical black holes, we determine constraints on $c_{\rm O}$ and ${\hat α}$ using the EHT data from Sgr. A* and M87*. We apply these constraints to reveal how the shadow radius behaves as the observer distance $r_O$ varies. It is revealed that black hole charge directly influences the shadow silhouette, but the symmergent parameters have a tenuous effect. We also explored the weak field regime by using the Gauss-Bonnet theorem to study the weak deflection angle caused by the M87* black hole. We have found that impact parameters comparable to the actual distance $D = 16.8$ Mpc show the potential detectability of such an angle through advanced astronomical telescopes. Overall, our results provide new insights into the behavior of charged black holes in the context of symmergent gravity and offer a new way to test these theories against observational data.

gr-qc↗

arXiv2023

Probing Geometric Proca in Metric-Palatini Gravity with Black Hole Shadow and Photon Motion

Extended metric-Palatini gravity, quadratic in the antisymmetric part of the affine curvature, is known to lead to the general relativity plus a geometric Proca field. The geometric Proca, equivalent of the non-metricity vector in the torsion-free affine connection, qualifies to be a distinctive signature of the affine curvature. In the present work, we explore how shadow and photon motion near black holes can be used to probe the geometric Proca field. To this end, we derive static spherically symmetric field equations of this Einstein-geometric Proca theory, and show that it admits black hole solutions in asymptotically AdS background. We perform a detailed study of the optical properties and shadow of this black hole and contrast them with the observational data by considering black hole environments with and without plasma. As a useful astrophysical application, we discuss constraints on the Proca field parameters using the observed angular size of the shadow of supermassive black holes M87$^*$ and Sgr A$^*$ in both vacuum and plasma cases. Overall, we find that the geometric Proca can be probed via the black hole observations.

gr-qc↗

arXiv2020

A Family-nonuniversal $U(1)^\prime$ Model for Excited Beryllium Decays

Excited beryllium has been observed to decay into electron-positron pairs with a $6.8~σ$ anomaly. The process is properly explained by a 17 MeV proto-phobic vector boson. In present work, we consider a family-nonuniversal $U(1)^{\prime}$ that is populated by a $U(1)^{\prime}$ gauge boson $Z^\prime$ and a scalar field $S$, charged under $U(1)^{\prime}$ and singlet under the Standard Model (SM) gauge symmetry. The SM chiral fermion and scalar fields are charged under $U(1)^{\prime}$ and we provide them to satisfy the anomaly-free conditions. The Cabibbo-Kobayashi-Maskawa (CKM) matrix is reproduced correctly by higher-dimension Yukawa interactions facilitated by $S$. The vector and axial-vector current couplings of the $Z^\prime$ boson to the first generation of fermions do satisfy all the bounds from the various experimental data. The $Z^\prime$ boson can have kinetic mixing with the hypercharge gauge boson and $S$ can directly couple to the SM-like Higgs field. The kinetic mixing of $Z^\prime$ with the hypercharge gauge boson, as we show by a detailed analysis, generates the observed beryllium anomaly. We find that beryllium anomaly can be properly explained by a MeV-scale sector with a minimal new field content. The minimal model we construct forms a framework in which various anomalous SM decays can be discussed.

hep-ph↗