arXiv subjects

Goksel Daylan Esmer

Publications and source records attributed to Goksel Daylan Esmer.

3 recordsLinked to original sources

arXiv2026

Dynamical Casimir Effect and Vacuum Friction in the Near-Horizon Geometry of a Black Hole

We investigate the Dynamical Casimir Effect (DCE) for a relativistic scalar field confined within a cavity possessing moving boundaries in the (1+1)-dimensional near-horizon geometry of a black hole. By applying a coordinate transformation, we map the moving-boundary problem to an equivalent acoustic metric with static boundaries, allowing for an exact canonical Hamiltonian formulation. We find that the local gravitational redshift fundamentally alters the vacuum structure, and the dynamical boundary motion induces time-dependent mode-mixing. When a boundary moves, it scatters the fluctuations of the ambient Hartle-Hawking state, generating a flux of created particles. Crucially, because the coordinate speed of light relative to the Killing time $t$ vanishes as one approaches the event horizon, we establish that maintaining physical, subluminal boundary motion requires the mechanical oscillation amplitude to scale proportionally with the proper distance to the horizon. Consequently, the effective Mach number of the moving mirror approaches zero in the near-horizon limit. Using a rigorous small-amplitude perturbative expansion and proper canonical operator normalization, we demonstrate that the transition probability into the field is heavily suppressed by a conformal geometric factor. Furthermore, we account for the Bose-enhancement caused by the thermal Hawking bath. While the thermal presence introduces infrared density-of-states enhancement, it remains insufficient to overcome the kinematic damping. Finally, we conclude that the extreme spacetime curvature acts to protect the near-horizon vacuum; the transition probability vanishes as the boundary approaches the event horizon, indicating a geometric and kinematic suppression of particle creation in the strong-gravity limit.

gr-qc↗

arXiv2026

Ergosphere Geometry and Thermodynamic Properties of Boosted Kerr-Taub-NUT Solutions in Kaluza-Klein Theory

We investigate rotating black holes obtained by applying a Kaluza-Klein boost to the Kerr-Taub-NUT spacetime and study the resulting four-dimensional geometry and thermodynamics after dimensional reduction. The boost along the compact direction generates an Einstein-Maxwell-Dilaton black hole in which the electric charge originates purely from higher-dimensional momentum rather than from an independent matter source. We demonstrate that the coordinate location of the stationary limit surface, defined by the condition $g_{tt}=0$ in the Einstein frame, is invariant under the Kaluza-Klein boost. Nevertheless, the boost induces a substantial enlargement of the \emph{physical} ergoregion, as measured by the proper spatial volume on constant-time hypersurfaces, through its modification of the induced spatial metric. We further verify the first law of black-hole thermodynamics with both the electric and magnetic Kaluza-Klein work terms included -- the latter being a genuinely dyonic feature generated by the interplay of the boost with the NUT charge -- and carefully distinguish the seed mass parameter from the asymptotic ADM mass and from the horizon Komar mass. Our results establish a clear separation between boost-invariant horizon thermodynamics and boost-dependent global geometric properties. In particular, higher-dimensional momentum enhances the effective inertial-frame rotation measured by ZAMOs and ergoregion volume without altering the horizon radius, entropy, or temperature, providing a clean geometric signature of extra dimensions in rotating black hole spacetimes.

gr-qc↗

arXiv2013

Hidden Symmetries and Geodesics of Kerr spacetime in Kaluza-Klein Theory

The Kerr spacetime in Kaluza-Klein theory describes a rotating black hole in four dimensions from the Kaluza-Klein point of view and involves the signature of an extra dimension that shows up through the appearance of the electric and dilaton charges. In this paper, we study the separability properties of the Hamilton-Jacobi equation for geodesics and the associated hidden symmetries in the spacetime of the Kerr-Kaluza-Klein black hole. We show that the complete separation of variables occurs only for massless geodesics, implying the existence of hidden symmetries generated by a second rank conformal Killing tensor. Employing a simple procedure built up on an "effective" metric, which is conformally related to the original spacetime metric and admits a complete separability structure, we construct the explicit expression for the conformal Killing tensor. Next, we study the properties of the geodesic motion in the equatorial plane, focusing on the cases of static and rotating Kaluza-Klein black holes separately. In both cases, we obtain the defining equations for the boundaries of the regions of existence, boundedness and stability of the circular orbits as well as the analytical formulas for the orbital frequency, the radial and vertical epicyclic frequencies of the geodesic motion. Performing a detailed numerical analysis of these equations and frequencies, we show that the physical effect of the extra dimension amounts to the significant enlarging of the regions of existence, boundedness and stability towards the event horizon, regardless of the classes of orbits.

gr-qc↗