Tekin Dereli

We investigate the thermodynamic and optical properties of Einstein-Born-Infeld-Anti-de Sitter (EBI-AdS) black holes (BHs). Our study derives the Hawking temperature using the standard surface gravity method and examines quantum corrections through both the Generalized Uncertainty Principle (GUP) and exponential entropy modifications, revealing enhanced thermal radiation and possible remnant formation scenarios. The gravitational redshift analysis disentangles the contributions of mass, cosmological constant, electromagnetic charge, and Born-Infeld (BI) nonlinear corrections, with the latter scaling as a ⁴ /r ⁶ and therefore becoming significant only in the near-horizon regime. Using the Gauss-Bonnet theorem, we compute the weak deflection angle of light in both vacuum and plasma media and show that dispersive effects may either enhance or suppress nonlinear electrodynamic signatures depending on the observational setup. In the extended phase-space formalism, where the BH mass is interpreted as enthalpy, the thermodynamic analysis reveals phase structures characterized by heat-capacity transitions between positive and negative regions, indicating local stability and instability depending on the parameter space. We further analyze BH heat engines operating in rectangular cycles and find efficiencies in the range η ~ 0.11–0.21, corresponding to approximately 30–61% of the associated Carnot efficiencies, consistent with other AdS BH systems. A comparison with Johnson's framework shows that BI-induced corrections to the heat-engine efficiency are typically of order 10 ^-12 for standard parameter choices, although they become appreciable in the strong-field regime where r _h ≲ 1.5 in Planck units. Finally, the plasma-lensing analysis reveals frequency-dependent refractive modifications encoded in the plasma parameter, thereby offering an additional observational channel for testing nonlinear electromagnetic effects in black-hole environments.

Linearized Einstein–Weyl equations are solved precisely in the context of sandwich gravitational waves. The neutrino’s energy-momentum depends on the geometry and composition of the gravitational pulse when it is scattered. Since the background remains unchanged at the test field level, the neutrino’s energy density will exhibit fluctuations between positive and negative extremes when traversing the sandwich wave. These variations could provide insights into the behavior of models concerning neutrino oscillations.

We study a six dimensional Kaluza Klein theory with spacetime topology M4×S2 and analyze the gauge sector arising from dimensional reduction. Using normalized Killing vectors on S2, we explicitly construct the reduced Yang Mills action and determine the corresponding gauge kinetic matrix. Despite the SO(3) isometry of S2, we show that only two physical gauge elds propagate in four dimensions. The gauge kinetic matrix therefore has rank two and possesses a single zero eigenvalue. We demonstrate that this degeneracy is a direct consequence of the coset structure S2 ≃ SO(3)/SO(2) and re ects a non dynamical gauge direction rather than an inconsistency of the reduction. Our results clarify the geometric origin of gauge degrees of freedom in Kaluza Klein reductions on coset spaces.

The metric tensor field equations for the general quadratic curvature gravity in four spacetime dimensions are derived by making use of the algebra of the exterior forms defined on the pseudo-Riemannian manifolds and the identities satisfied by the Riemann curvature tensor. The linearized metric field equations are formulated in terms of the perturbation 1-form fields.