arXiv subjects

Reggie C. Pantig

Publications and source records attributed to Reggie C. Pantig.

At least 37 records · Page 2Linked to original sources

arXiv2026

Josephson's effect in the Schwarzschild background

We develop a fully covariant, analytic framework for Josephson phenomena in static curved spacetimes and specialize it to the Schwarzschild exterior. The formulation rests on two invariant elements: the gauge-invariant condensate momentum that governs phase dynamics and the conserved current whose hypersurface flux encodes transport for an observer at infinity. Using the timelike Killing field to relate proper and asymptotic quantities, we derive a redshifted AC Josephson law in which the asymptotic phase-evolution rate is proportional to the difference of redshifted voltage drops, i.e. to $V_i^\infty \equiv α_i V_i^{\rm proper}$; equivalently, it depends on $α_i V_i^{\rm proper}$ for local control. Under RF drive specified at infinity, the Shapiro-step loci are invariant (expressed in asymptotic voltages) while propagation phases set any apparent lobe translation. For DC transport, a short-junction solution on a static slice yields the proper current-phase relation; mapping to asymptotic observables gives a single-power redshift scaling of critical currents, $I_{c,\infty}\propto αI_c^{\rm proper}$, whereas power scales as $P_\infty\propto α^2 P_{\rm proper}$. In a "vertical" dc-SQUID with junctions at different radii, gravity does not shift the DC interference pattern at linear order; it produces a small envelope deformation and an amplitude rescaling. Gravity does not alter the local Josephson microphysics; it reshapes the clocks and energy accounting that define measurements at infinity. The resulting predictions are gauge- and coordinate-invariant, operationally stated in terms of an experimenter who can control (proper vs. asymptotic bias), and remain analytic from the weak-field regime to the near-horizon limit.

hep-th↗

arXiv2026

Semi-Analytic Trajectory Analysis of Light in Generic Static Spacetimes

We study a unified semi-analytical framework to study null geodesics and weak-field light deflection in generic static, spherically symmetric spacetimes of the form $ds^2 = -α(r,δ)\,dt^2 + γ(r,δ)\,dr^2 + β(r,δ)\,dΩ_2^2,$ where $α$, $β$, and $γ$ encode model-dependent deviations from Schwarzschild gravity inspired from [Phys.Rev.D 112 (2025) 12, 124072]. Starting from the exact first-order orbit equation, we derive a compact master equation for the impact-parameter-dependent trajectory $u(φ)\equiv 1/r(φ)$ and obtain a model-independent expression for the bending angle $α(b)$ in terms of generic metric functions and their derivatives. This master equation is then solved semi-analytically by three complementary techniques: (i) the homotopy perturbation method (HPM), (ii) the variational iteration method (VIM), and (iii) a calibrated impulse (single-kick) approximation expressed directly in terms of the effective gravitational potential. As nontrivial test beds we consider a scalar-hairy Reissner-Nordström-like black hole where the scalar hair enters as $Q_s$ in an effective charge parameter. Then we derive closed-form expressions for the deflection angle, identify the leading scalar-hair, and compare the accuracy and convergence properties of HPM, VIM, and the impulse method against the standard Schwarzschild limits. Our results show that the generic formulation in $(α,β,γ)$ can efficiently accommodate a broad class of modified gravity black hole solutions. We further supplement the analytic treatment with a compact numerical results against the exact null-geodesic integral near the photon sphere in order to delineate the practical range of validity of the three approximation schemes.

gr-qc↗

arXiv2026

Boundary-only weak deflection angles from isothermal optical geometry

We develop a boundary only method for computing weak gravitational deflection angles at finite source and receiver distances within the Gauss-Bonnet theorem formulation of optical geometry. Exploiting the fact that the relevant equatorial optical manifold is two dimensional, we introduce isothermal (conformal) coordinates in which the optical metric is locally conformal to a flat reference metric and the Gaussian curvature reduces to a Laplacian of the conformal factor. Such an identity converts the curvature area term in the Gauss-Bonnet theorem into a pure boundary contribution via Green/Stokes-type relations, yielding a deflection formula that depends only on boundary data and controlled closure terms. The residual normalization freedom of the isothermal radius is isolated as an additive freedom in the conformal factor and is shown to leave physical observables invariant, eliminating the need for orbit dependent calibration prescriptions. We explicitly implement the boundary only formalism in weak deflection, where the leading bending reduces to elementary one-dimensional integrals evaluated on a flat reference ray in the conformal plane, with finite distance dependence entering solely through endpoint data. We validate the construction by reproducing finite distance weak deflection for Schwarzschild, deriving the leading finite distance charge correction for Reissner-Nordström, and applying the same boundary only framework to the Kottler (Schwarzschild-de Sitter) geometry as a representative non-asymptotically flat test case, recovering the standard finite distance expansion including the explicit $\mathcal{O}(Λ)$ and mixed $\mathcal{O}(ΛM)$ contributions to the total deflection angle.

gr-qc↗

arXiv2026

Reference-renormalized curvature-primitive Gauss-Bonnet formalism for finite-distance weak gravitational lensing in static spherical spacetimes

We develop a reference-renormalized (photon-sphere-free) normalization scheme for Gauss-Bonnet gravitational lensing at finite distance in static, spherically symmetric spacetimes. The method treats the curvature primitive used to reduce the Gauss-Bonnet curvature-area integral as a quantity defined only modulo an additive constant (an additive gauge freedom). We fix this gauge by matching to a physically chosen reference optical geometry in an outer regime where the physical geometry approaches that reference, thereby defining a unique renormalized discrepancy primitive $\mathcal{P}_e(r)$ by reference subtraction. The resulting master formula yields the Ishihara-Li finite-distance deflection angle without invoking any circular null orbit, while remaining fully compatible with orbit-normalized prescriptions whenever a suitable photon sphere exists (the two gauges differ only by a constant shift and give identical $α$). In asymptotically flat settings the canonical reference is Minkowski, while in Kottler-type backgrounds the canonical reference is de Sitter within the static patch, making the operational fiducial explicit. We validate the method by reproducing Ishihara's finite-distance weak-deflection formulas for Schwarzschild, Reissner-Nordström, and Kottler spacetimes, including the mixed $r_gΛ$ term in the Kottler case within the static-patch fiducial. We also present a demonstrative example in which orbit normalization is genuinely inapplicable because no circular null orbit exists in the physical optical region (the Janis-Newman-Winicour spacetime for $γ\le \tfrac12$). The result is a unified, geometrically transparent route to finite-distance lensing that preserves compatibility with orbit-normalized prescriptions whenever those apply.

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arXiv2026

Horizon brightened acceleration radiation from massive vector fields

In this paper, we develop a quantum-optical treatment of acceleration radiation for atoms freely falling into a Schwarzschild black hole when the ambient field is a massive spin-1 (Proca) field. Building on the HBAR framework of Scully and collaborators, we analyze two detector realizations: a charged-monopole current coupling and a physical electric-dipole coupling, both within a cavity that isolates a single outgoing Schwarzschild mode prepared in the Boulware state. Using a near-horizon stationary-phase analysis, we show that the thermal detailed-balance factor governing excitation versus absorption is universal and depends only on the near-horizon Rindler coordinate transformation. At the same time, the absolute spectra acquire distinctive Proca signatures: a hard mass threshold, polarization-dependent prefactors, and axial/polar graybody transmissions. Promoting single-pass probabilities to escaping rates yields a master equation whose steady state is geometric and whose entropy flux obeys an horizon brightened acceleration radiation-style area-entropy relation identical in form to the scalar case, with all vector-field specifics entering through the radiative area change. Our results provide a controlled pathway to probe longitudinal versus transverse responses, mass thresholds, and the role of polarization-resolved graybody transmission in acceleration radiation. More precisely, we derive the universal near-horizon kernel and show how the Proca transmission data enter the escaping probabilities, rates, and entropy flux; a dedicated numerical computation of the axial/polar graybody profiles is left for future work. This sets the stage for extensions to rotating backgrounds, alternative exterior states, and detector-engineering strategies.

gr-qc↗

arXiv2026

Josephson Effects in Slowly Rotating Spacetimes

We investigate Josephson phenomena in a slowly rotating stationary spacetime, emphasizing the distinct roles of gravitational redshift and rotational frame dragging motivated by [10.1007/JHEP02(2026)006]. Using a covariant formulation based on gauge-invariant phase dynamics and conserved currents within a $3+1$ decomposition, we analyze both AC and DC Josephson effects and interferometric configurations. Restricting attention to linear order in the rotation parameter $a$, and working in the Eulerian/ZAMO frame, we show that in the slow-rotation slicing adopted here the lapse function agrees with its static (Schwarzschild-type) form up to $\mathcal{O}(a^2)$, while rotational effects enter through the shift vector. Consequently, redshift effects on Josephson frequencies and DC critical currents remain unchanged relative to the non-rotating case at $\mathcal{O}(a)$. The AC Josephson relation retains its redshifted structure when expressed in terms of proper voltages and reduces to the standard flat-spacetime form when formulated in terms of asymptotic (Killing-time) observables. Likewise, the DC critical current measured at infinity scales with a single power of the lapse function and is unaffected by rotation at linear order in the absence of azimuthal condensate momentum. Rotational effects become relevant only in configurations sensitive to spatial phase transport or to synchronization with respect to the global time coordinate. In particular, RF-driven interferometric setups can acquire Sagnac-type phase offsets associated with frame dragging, whereas the DC fluxoid constraint remains unshifted at linear order in the present approximation. Our results provide a clean separation between lapse-driven redshift effects and shift-driven rotational contributions in Josephson physics and furnish a consistent framework for superconducting circuits in stationary spacetimes.

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arXiv2026

Shadow Ringing of Black Holes from Photon Sphere Quasinormal Modes

The recent convergence of gravitational-wave (GW) observations and black hole imaging provides complementary probes of strong-gravity dynamics. While the black hole shadow is typically modeled as a static feature, a dynamically perturbed spacetime in its ringdown phase must induce temporal modulations in the shadow's apparent size and shape. We develop a theoretical framework within linear perturbation theory to investigate this shadow ringing effect for a Schwarzschild black hole. By modeling the geometry as a small, mode-selected quasinormal mode (QNM) perturbation, we treat the shadow boundary as an instantaneous separatrix of null geodesics. We derive a first-order, gauge-invariant mapping between the metric perturbation $h_{μν}$ and the displacement of the shadow boundary, $δR(φ,t)$. By perturbing the effective potential for null geodesics near the unstable photon sphere ($r=3M$), we derive mode-resolved transfer coefficients that quantify how the QNM imprints itself onto the shadow. We predict that the shadow boundary oscillates coherently at the QNM's real frequency $ω_{\rm Re}$ with an exponential damping rate set by $|ω_{\rm Im}|$. Furthermore, the azimuthal structure of the modulation encodes the spherical harmonic content $(\ell,m)$ of the driving QNM, providing a novel, geometric signature for QNM spectroscopy.

hep-th↗

arXiv2026

Gauss-Bonnet lensing of spinning massive particles in static spherically symmetric spacetimes

We extend the finite-distance Jacobi-metric Gauss-Bonnet framework of Li \textit{et al}. [10.1103/PhysRevD.101.124058] to massive test particles carrying intrinsic spin. At pole-dipole order, the Mathisson-Papapetrou-Dixon dynamics generically drives the spatial ray away from Jacobi geodesics, so the standard Gauss-Bonnet construction must be reformulated to accommodate a non-geodesic particle boundary. Working in the aligned-spin planar sector with the Tulczyjew-Dixon spin supplementary condition and retaining terms linear in the spin, we derive a spin-generalized deflection identity in which the spin dependence enters through a single additional boundary functional: the geodesic-curvature integral of the physical ray in the Jacobi manifold. We show that Li's circular-orbit boundary choice remains fully compatible with this generalization and continues to collapse the Gaussian-curvature surface term to an effective one-dimensional integral. We then provide an implementation-ready weak-field recipe that relates the required geodesic curvature directly to the MPD spin-curvature force, enabling systematic perturbative evaluation without introducing model-dependent definitions of asymptotic angles. As applications, we validate the Schwarzschild limit, including the expected linear-in-spin weak-field scaling, and compute leading spin corrections for Reissner-Nordström and Kottler (Schwarzschild-de Sitter) geometries with finite source and receiver distances. In Kottler, we show that the constant-curvature part of the cosmological constant does not generate a linear-in-spin MPD force under the Tulczyjew-Dixon condition; nevertheless, the finite-distance spin correction acquires an explicit $Λ$-dependence through the Jacobi-metric prefactor entering the Gauss-Bonnet boundary functional, in addition to the Weyl-driven (mass-sourced) contribution.

gr-qc↗

arXiv2026

Horizon-Brightened Acceleration Radiation and Optical Signatures of Generic Regular Black Holes from Nonlinear Electrodynamics

We investigate horizon-brightened acceleration radiation (HBAR) and optical signatures for a broad class of regular black holes sourced by nonlinear electrodynamics. The spacetimes considered are static, spherically symmetric, and nonsingular, and they include Bardeen-like, and Hayward-like regular black-hole limits as spacial cases. We characterize the horizon structure and thermodynamics properties, and we compute key optical observables by determining the photon-sphere location and the corresponding shadow size as seen by distant observers, including controlled perturbative limits and full numerical solutions. Using angular-size constraints for SgrA* and M87* from the Event Horizon Telescope and the GRAVITY collaboration, we perform a Markov Chain Monte Carlo analysis to infer the admissible parameter ranges of the model and to quantify degeneracies among the black-hole mass and nonlinear-electrodynimcs parameters. On the quantum side, we develop the near-horizon reduction relevant for HBAR, showing that the dominant sector governing the detector response exhibits conformal behavior and leads to a thermal excitation spectrum governed by the horizon temperature. We formulate a Lindblad master-equation description of the radiation field, identify the thermal steady state, and derive an HBAR entropy-energy relation consistent with a Clausius-type first law. Finally, we establish a Wien-type displacement law for the HBAR spectrum, expressing the peak wavelength in terms of the horizon thermodynamics, thereby providing an additional observable link between nonlinear electrodynamics, regularity, and near-horizon quantum radiation.

gr-qc↗

arXiv2026

Radial Integral Reformulation of the Gauss-Bonnet Weak Deflection Angle at Finite Distance

We develop a radial integral reformulation of finite distance gravitational lensing in optical geometry for static, spherically symmetric spacetimes. Starting from the Gauss-Bonnet characterization of the finite distance deflection angle, we adopt the Li-type curvature primitive identity [https://doi.org/10.1103/PhysRevD.101.124058] [2006.13047], which reduces the curvature-area contribution to a one-dimensional integral evaluated along the physical light ray. We then remove the remaining implicit orbit dependence by an explicit change of variables using the null first integrals, converting the Li line integral from $ϕ$-integration to $r$-integration and splitting the trajectory at the turning point (closest approach). The resulting formula expresses the deflection angle as a sum of two radial integrals over $[r_0,r_S]$ and $[r_0,r_R]$ plus the finite distance angular bookkeeping term, with a transparent normalization/cancellation structure for the curvature primitive. In Schwarzschild gauge, we provide a weak-field evaluation toolkit that reduces the computation to reusable families of standard radial integrals and gives compact expressions for the endpoint incidence angles in the optical metric. Worked examples include Schwarzschild and Kottler (Schwarzschild-de Sitter) spacetimes and a black hole immersed in perfect-fluid dark matter with a finite halo. For the finite-halo model we derive closed-form leading weak-deflection expressions for mixed endpoint configurations (source/receiver inside or outside the halo), illustrating the modularity of the radial Gauss-Bonnet pipeline.

gr-qc↗

arXiv2026

Finite Distance Corrections to Vacuum Birefringence in Strong Gravitational and Electromagnetic Fields

We study polarization dependent photon propagation in static, spherically symmetric spacetimes permeated by strong magnetic fields, with the aim of quantifying how finite emission and detection radii modify vacuum birefringence signals. Working in the geometric optics limit of NLED, we formulate the two polarization modes as null geodesics of distinct effective (optical) metrics. We then develop a controlled weak-coupling expansion that cleanly separates the standard gravitational deflection from the birefringent contribution induced by the electromagnetic nonlinearity. Using a finite distance Gauss-Bonnet construction on the associated optical manifolds, we derive a general expression for the differential bending angle in which the source and observer are kept at arbitrary radii, thereby extending the usual scattering-at-infinity treatment. As benchmark applications, we specialize our results to the Euler-Heisenberg effective action of quantum electrodynamics (QED) and to Born-Infeld electrodynamics. We find that the observable birefringence is generically reduced by finite-distance truncation of the curvature flux, and we provide explicit correction series suitable for data analysis. For magnetar-motivated dipole-like falloff, the same geometric truncation can reduce the predicted polarization-dependent deflection at the order-tens-of-percent level for surface/near-surface emission; in a simple one-sided (outward-only) benchmark the suppression can approach 1/2 for near-limb rays. Since realistic dipole magnetospheres are axisymmetric rather than spherically symmetric, we present this as an illustrative scaling estimate and leave a fully axisymmetric treatment to future work. Our results furnish a necessary finite-distance calibration for interpreting current and future X-ray polarimetry measurements and for placing unbiased constraints on strong-field QED and broader NLED parameters.

gr-qc↗

arXiv2026

Acceleration Radiation of Freely Falling Atoms: Nonlinear Electrodynamic Effects

Motivated by the work of Scully \textit{et al.} [ \textcolor{blue}{Proc. Nat. Acad. Sci. 115, 8131 (2018)}] and Camblong \textit{et al.}[ \textcolor{blue}{Phys. Rev. D 102, 085010 (2020)}], we investigate horizon-brightened acceleration radiation (HBAR) for freely falling two-level atoms in the geometry of a Bardeen regular black hole. Building on the quantum-optics approach to acceleration radiation and its near-horizon conformal quantum mechanics (CQM) structure, we show that the dominant physics is again governed by an inverse-square potential in the radial Klein-Gordon equation, with an effective coupling fixed by the Bardeen surface gravity. Using geodesic expansions and a near-horizon CQM reduction of the scalar field, we derive the excitation probability for atoms falling through a Boulware-like vacuum in the presence of a stretched-horizon mirror. The resulting spectrum is Planckian in the mode frequency, with a temperature determined by the Bardeen Hawking temperature. We analyze how the regular core parameter controls the strength of the radiation and demonstrate that the excitation probability is strongly suppressed as the geometry approaches the extremal (cold remnant) limit. Numerical results illustrate the dependence of the spectrum on the Bardeen parameter and on the atomic transition frequency.

gr-qc↗

arXiv2025

Gravitational Black Hole Shadow Spectroscopy

In this work, we develop a generalized perturbative framework for gravitational shadows in static, spherically symmetric spacetimes. Building upon the recent two-parameter perturbative framework of Kobialko et al. \cite{Kobialko:2024zhc}, this work extends the expansion in particle energy and metric deviation to encompass arbitrary, simultaneous deformations of all metric functions. By relaxing the common restriction of a fixed area radius $(β(r) = r^2)$, our formalism applies to a significantly broader class of alternative gravity theories and exotic compact objects. We derive analytical formulae for the massive shadow radius up to the second order in the deformation parameter, explicitly revealing the phenomenological signatures that arise from the coupling between temporal and spatial metric perturbations. The key result is that the distinct energy dependence of the massive shadow provides a powerful method to disentangle these different types of geometric deformations, breaking observational degeneracies inherent in the photon shadow alone. We demonstrate this principle with applications to traversable wormholes and canonical scalar-tensor solutions, showing how each produces a unique, distinguishable energy-dependent fingerprint. This generalized framework provides a robust, theory-agnostic tool for testing strong-field gravity. It offers a clear methodology for reconstructing metric parameters from potential multi-messenger observations of massive particle shadows.

hep-th↗

arXiv2025

The Sound of an Orbit: A Quantum Spectrum at the ISCO

We investigate the quantum signature of the innermost stable circular orbit (ISCO), a region of profound importance in black hole astrophysics. By modeling an atom as an Unruh-DeWitt detector coupled to a massless scalar field in the Boulware vacuum, we calculate the excitation rate for a detector following a circular geodesic at the ISCO of a Schwarzschild black hole. In stark contrast to the continuous thermal spectra associated with static or infalling observers, our analysis reveals a unique, non-thermal excitation spectrum characterized by a discrete "frequency comb" of sharp, resonant peaks. We show that the locations of these peaks are determined by the orbital frequency at the ISCO, while their intensity increases dramatically as the orbit approaches this final stability boundary. This distinct spectral signature offers a novel theoretical probe of the quantum vacuum in a strong-field gravitational regime and provides a clear distinction between the quantum phenomena experienced by observers on different trajectories. Our findings have potential implications for interpreting the emission spectra from accretion disks and open new avenues for exploring the connection between quantum mechanics and gravity.

gr-qc↗

arXiv2025

HBAR entropy of Infalling Atoms into a GUP-corrected Schwarzschild Black Hole and equivalence principle

In this work, we have investigated the phenomenon of acceleration radiation exhibited by a two-level atom freely falling into a Generalized Uncertainty Principle (GUP)-corrected Schwarzschild black hole. We derive analytic expressions for the atom's excitation probability with simultaneous emission of a scalar quantum and observe that it satisfies the Einstein equivalence principle when compared to the excitation probability induced by a uniformly accelerating mirror, motivated by studies [10.1103/PhysRevLett.121.071301] and [10.1073/pnas.1807703115]. Adopting an open-quantum-system framework, we then compute the horizon-brightened acceleration radiation (HBAR) entropy for the GUP-corrected spacetime and find that it reproduces the Bekenstein-Hawking entropy law, with corrections characteristic of GUP effects. These results underline the robustness of thermal radiation processes near horizons and the universality of entropy corrections in quantum-improved black hole spacetimes.

gr-qc↗

arXiv2025

Acceleration radiation from vibrating atoms in Schwarzschild spacetime

Motivated by the work of Scully \textit{et al.} [ \textcolor{blue}{Proc. Nat. Acad. Sci. 115, 8131 (2018)}] and Dolan \textit{et al.}[ \textcolor{blue}{New J. Phys. 22, 033026 (2020)}], we study the acceleration radiation from a two-level Unruh-DeWitt detector that undergoes small-amplitude radial oscillations at fixed mean radius $R_0$ outside a Schwarzschild black hole. The massless scalar field is quantized in the Boulware vacuum to isolate curvature-modulated acceleration effects without a thermal Hawking background. Working in a (1+1) radial reduction and using first-order time-dependent perturbation, we evaluate the period-averaged transition rate (or the Floquet transition rate). The resulting particle emission spectrum exhibits a thermal Bose-Einstein-type profile with periodic trajectory yielding a Floquet resonance condition $nΩ> ω_0$ and a closed-form expression for the Floquet transition rate $\overline{P}_n$, which reduces to the flat Minkowski spacetime result as $R_0\to\infty$, in agreement with Near the horizon, $f(R_0)<1$ enhances the effective Bessel argument by $1/\sqrt{f(R_0)}$, providing a simple analytic demonstration of curvature/redshift amplification of acceleration radiation. In particular, the spectrum weighted by the Bessel function becomes ill-defined near the black hole horizon as $R_{0}\rightarrow 2M$, possibly manifesting the well-known pathological behavior of the Boulware vacuum state. We discuss the regime of validity (small amplitude, $R_0$ away from the horizon) and outline the extensions to (3+1) dimensions, including density-of-states and greybody factors, and to alternative vacuum choices. Our results offer an analytically tractable link between flat-space vibrating atom proposals and black-hole spacetimes.

gr-qc↗

arXiv2025

Acceleration Radiation from Derivative-Coupled Atoms Falling in Modified Gravity Black Holes

The interaction of quantum detector models with fields in curved spacetimes provides fundamental insights into phenomena such as Hawking and Unruh radiation. While standard models typically assume a minimal coupling between the detector and the field, physically motivated derivative couplings, which are sensitive to field gradients, have been less explored, particularly in the context of modified gravity theories. In this paper, we develop a general framework to analyze the acceleration radiation from a two-level atomic detector with a derivative coupling undergoing a radial geodesic infall into a generic static, spherically symmetric black hole. We derive a general integral expression for the excitation probability and apply it to two distinct spacetimes. For an extended uncertainty principle (EUP) black hole, we demonstrate that the detector radiates with a perfect thermal spectrum at the precise Hawking temperature, reinforcing the universality of this phenomenon. For a black hole solution in a Ricci-coupled Bumblebee gravity model, the radiation is also thermal. Still, its temperature is modified in direct correspondence with the theory's Lorentz-violating parameters, consistent with the modified Hawking temperature. Furthermore, we demonstrate that derivative coupling results in a significantly enhanced entropy flux compared to minimal coupling models. Our results establish acceleration radiation as a sensitive probe of near-horizon physics and demonstrate that this phenomenon can provide distinct observational signatures to test General Relativity (GR) and alternative theories of gravity in the strong-field regime.

gr-qc↗

arXiv2025

Multimodal signatures of asymptotic (A)dS Kalb-Ramond black holes: Constraints through the shadow, weak deflection angle, and topological photon spheres

This study explores novel static, neutral black hole solutions within Kalb-Ramond (KR) gravity in asymptotically (anti-)de Sitter [(A)dS] spacetimes, incorporating spontaneous Lorentz symmetry breaking (LSB) via an antisymmetric tensor field. Focusing on two metric configurations, we derive general analytical expressions for the horizon radius, photon sphere, shadow radius, and weak gravitational deflection angle. The universality of these expressions enables their applicability to a broad class of non-rotating spacetimes beyond KR gravity. By confronting these models with empirical data from the Event Horizon Telescope (EHT) and Solar System experiments, the work yields tight constraints on the Lorentz-violating parameter $\ell$, demonstrating that certain parameterizations - particularly Case B - yield observationally viable and physically consistent outcomes. Additionally, we employ topological methods to analyze black hole thermodynamics and photon sphere stability, uncovering critical geometrical structures in both thermodynamic and optical contexts. These multimodal signatures collectively offer a powerful framework for testing Lorentz-violating extensions of General Relativity (GR) and highlight the potential of topological diagnostics in gravitational physics.

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