We study massless scalar perturbations of rotating anti-de Sitter black strings sourced by a power-Maxwell field with negative exponent $s$. The charge enters the metric function as $-Qr^{p}$ with $p=2/(1-2s)$, and the case $s=-1/2$ gives a linear term with an algebraic horizon. Since rotation is a local boost of the static string, the rotating spectrum follows exactly from the static one evaluated at a frequency-dependent momentum. We compute the spectrum with the Horowitz-Hubeny series, Chebyshev collocation and time-domain evolution, each implemented in two independent codes and checked against the planar Schwarzschild-AdS limit. The charge acts in two ways. At the reduced charge $\hat q_c=0.72626$ the least damped pair of modes meets on the imaginary axis, so more strongly charged strings ring down without oscillation, and at the endpoint of the branch the spectrum is exactly hypergeometric. At large transverse momentum the distance of the modes from the light cone grows as $k^{1/(1-4s)}$, replacing the $k^{-1/5}$ law of the neutral brane. Rotation continues the exceptional point into a line in the plane of charge and rotation, adds a purely damped axisymmetric tower, and never produces superradiant growth. A near-horizon estimate used earlier for this geometry misses all of these effects.
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The paper asks how nonlinear electrodynamics changes massless-scalar quasinormal modes of rotating AdS black strings, beyond an earlier near-horizon approximation. It studies the negative-exponent power-Maxwell branch, whose metric contains $-Qr^p$, with $p=2/(1-2s)\in(0,2)$, focusing on $s=-1/2$. Rotation is incorporated through an exact boost relation: rotating frequencies satisfy the static spectral equation at frequency-dependent, generally complex transverse momentum.
For the static $s=-1/2$ string at zero momentum, the fundamental pair coalesces at $\hat q_c=0.72625663$, with $\omega_c l^2/r_H=-1.7296186i$, then splits into purely damped modes. At the massless-background endpoint $\hat q=1$, a hypergeometric solution gives $\omega_n=-i(r_H/l^2)(n+1)(n+3)/[2(n+2)]$. A near-boundary scaling analysis yields $\omega-k\propto k^{1/(1-4s)}$ at any nonzero reduced charge, replacing the neutral $k^{-1/5}$ behavior and eliminating its asymptotically long-lived high-momentum modes. Rotation produces a purely damped axisymmetric tower and extends the exceptional point into a curve reaching $\hat q\simeq0.465$ before folding.
Spectra are checked using Horowitz–Hubeny series, Chebyshev collocation and time-domain evolution, each independently implemented twice, with neutral and exact-endpoint benchmarks. No growing modes are found in the reported rotating scan, $0\le a/l\le3$, $|m|\le1$, at $\hat q=0,0.5$; the geometry satisfies $\Omega_Hl<1$ for all rotation. The analysis concerns a massless test scalar only: electromagnetic and gravitational stability, nonlinear dynamics and observational ringdown are not established. The exceptional curve is not fully mapped beyond its fold.
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Error found: The abstract's overdamping statement needs restriction to the static s=-1/2, zero-transverse-momentum sector used to obtain the threshold 0.72625663, because the paper itself establishes oscillatory large-momentum modes even above that charge.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
We study massless scalar perturbations of rotating anti-de Sitter black strings sourced by a power-Maxwell field with negative exponent s. The charge enters the metric function as −Qrp with p=2/(1−2s), and the case s=−1/2 gives a linear term with an algebraic horizon. Since rotation is a local boost of the static string, the rotating spectrum follows exactly from the static one evaluated at a frequency-dependent momentum. We compute the spectrum with the Horowitz-Hubeny series, Chebyshev collocation and time-domain evolution, each implemented in two independent codes and checked against the planar Schwarzschild-AdS limit. The charge acts in two ways. At the reduced charge q^c=0.72626 the least damped pair of modes meets on the imaginary axis, so more strongly charged strings ring down without oscillation, and at the endpoint of the branch the spectrum is exactly hypergeometric. At large transverse momentum the distance of the modes from the light cone grows as k1/(1−4s), replacing the k−1/5 law of the neutral brane. Rotation continues the exceptional point into a line in the plane of charge and rotation, adds a purely damped axisymmetric tower, and never produces superradiant growth. A near-horizon estimate used earlier for this geometry misses all of these effects.
The paper asks how nonlinear electrodynamics changes massless-scalar quasinormal modes of rotating AdS black strings, beyond an earlier near-horizon approximation. It studies the negative-exponent power-Maxwell branch, whose metric contains −Qrp, with p=2/(1−2s)∈(0,2), focusing on s=−1/2. Rotation is incorporated through an exact boost relation: rotating frequencies satisfy the static spectral equation at frequency-dependent, generally complex transverse momentum.
For the static s=−1/2 string at zero momentum, the fundamental pair coalesces at q^c=0.72625663, with ωcl2/rH=−1.7296186i, then splits into purely damped modes. At the massless-background endpoint q^=1, a hypergeometric solution gives ωn=−i(rH/l2)(n+1)(n+3)/[2(n+2)]. A near-boundary scaling analysis yields ω−k∝k1/(1−4s) at any nonzero reduced charge, replacing the neutral k−1/5 behavior and eliminating its asymptotically long-lived high-momentum modes. Rotation produces a purely damped axisymmetric tower and extends the exceptional point into a curve reaching q^≃0.465 before folding.
Spectra are checked using Horowitz–Hubeny series, Chebyshev collocation and time-domain evolution, each independently implemented twice, with neutral and exact-endpoint benchmarks. No growing modes are found in the reported rotating scan, 0≤a/l≤3, ∣m∣≤1, at q^=0,0.5; the geometry satisfies ΩHl<1 for all rotation. The analysis concerns a massless test scalar only: electromagnetic and gravitational stability, nonlinear dynamics and observational ringdown are not established. The exceptional curve is not fully mapped beyond its fold.
We study charged massive scalar field perturbations on the rotating black hole (BH) background of Einstein-Maxwell-Dilaton-Axion (EMDA) theory, known as the Kerr-EMDA BH. Starting from the gauge-covariant Klein-Gordon equation (KGE), we perform a full separation of variables and obtain exact analytical solutions for both the angular and radial parts in terms of confluent Heun functions (CHFs). Unlike the earlier neutral scalar treatment by Senjaya and Ponglertsakul [Eur. Phys. J. C \textbf{85}, 352 (2025)], the electromagnetic coupling q fundamentally alters the structure of the Heun parameters and produces qualitatively new physics. Applying the CHF polynomial condition, we derive the resonant frequency spectrum whose imaginary parts are equispaced with ∣ΔωI∣=1/(2M), a universal spacing determined solely by the BH mass. Via the Maggiore prescription and the first law of BH thermodynamics, this yields a parameter-dependent entropy quantum δSBH=4πr+/(r+−r−), which reduces to 4π for Schwarzschild but diverges at extremality -- {\color{black}in contrast to the universal 2π obtained for the rotating linear dilaton BH (RLDBH).} We construct the effective potential governing scalar wave scattering and analyze its dependence on the dilaton parameter D, rotation a, and scalar charge q. In the massless uncharged limit, the CHF reduces to the Gauss hypergeometric function, {\color{black}enabling us to compute the first analytical greybody factor (GF) for the Kerr-EMDA geometry; we show that this reduction extends to massless charged scalars, yielding a closed-form GF that captures superradiant amplification.} We examine how the dilaton deformation distinguishes the Kerr-EMDA spectrum from the standard Kerr and Kerr-Newman cases.
We apply the complex scaling method to black-hole perturbations in four-dimensional Schwarzschild--de~Sitter (dS) spacetimes. The method converts the outgoing-wave boundary-value problem into a non-Hermitian spectral problem and enables quasinormal-mode poles and the rotated continuum to be treated in a common framework. We focus in particular on the continuum level density, which characterizes the continuum response beyond isolated quasinormal-mode frequencies. Using Regge--Wheeler-type perturbation equations for scalar, electromagnetic, and gravitational fields, we investigate how a nonzero cosmological constant modifies the pole and continuum sectors. We also discuss a possible extension to string-inspired coupled-channel systems, and illustrate that higher-dimensional dS black holes can be treated within the same framework, at least in tensor- and vector-type sectors. Our results indicate that complex scaling offers a useful spectral framework for analyzing both quasinormal modes and continuum response in black-hole physics.
We study the quasinormal-mode and quasibound-state spectra of a massless scalar field in weakly magnetized Ernst--Schwarzschild spacetime. In the separated O(B02) regime, the Klein--Gordon equation reduces to a radial confluent-Heun equation. We construct an endpoint-selected spectral Wronskian directly from the canonical confluent-Heun recurrence and its regular-to-irregular connection limit. Quasinormal modes and quasibound states are then obtained as zeros of the same analytic spectral function on the radiative and bound sheets, respectively, providing a unified treatment of the two spectral sectors within the separated weak-field problem. The resulting QNM and QBS frequencies agree with independent weak-field Ernst and massive-Schwarzschild benchmarks available in the literature. We further show, for representative cases, that the frequencies selected by the local Heun-series termination relation examined here do not satisfy the endpoint-selected quasibound-state condition. The construction therefore provides a direct horizon-to-infinity spectral condition for both radiative and bound states within the weak-field Ernst problem.
We expand the Einstein--Hilbert action to cubic order about the Schwarzschild horizon, in the even Regge--Wheeler gauge of the Gaddam--Groenenboom--'t~Hooft near-horizon framework, and derive the cubic graviton self-interaction. Our central result is a vanishing theorem: at leading soft order the self-coupling of the purely traceless longitudinal polarizations is identically zero. This is a framework-specific statement: even RW gauge, GGV sector, leading soft order. The surviving interaction lives in the trace sector; its on-shell equal-ℓ weight W(λ,λ,λ)=−3λ(2λ2+λ+3)/(λ+1)2, follows from two independent derivations agreeing to machine precision. We simulate the resulting Hamiltonian at two complementary scales. On IBM Qiskit/Aer, with exact cross-checks, the hardware-format circuits confirm quantitatively what two structural facts already predict, a conserved charge that only the cubic vertex violates (opening φφ→hh→4φ) and a resonance-free boost spectrum (gap →1/2): the longitudinal channel is perturbatively rigid, and the simulation measures the residual dressing (deff=1.06; multiplicity far from thermal, Poisson, and Haar). A symmetry-graded matrix-product-state evolution then climbs the multipole ladder to sixty modes, the 120-qubit register, and settles the one question the multiplet cannot: on a late-time measure common to both engines the inelasticity converges to ηˉ∞≃0.16 (understated by the single multiplet), the dressing stays area-law with peak entanglement ≃0.45 nats far below the Page value, and the result is cutoff-converged and robust to 96 qubits at larger occupation. The rigidity therefore persists rather than scrambling as the register grows.
We study entanglement degradation near the horizons of regular, Reissner-Nordström, and Schwarzschild-de Sitter black holes, considering the Bardeen, Hayward, and generalized Hayward metrics as regular black holes. To this end, we compute the entanglement negativity, N, for two Unruh-like modes of a scalar field shared by Alice, who is inertial, and Rob, who hovers at a fractional offset ρ outside the horizon of the backgrounds under consideration. For each geometry, we locally approximate the metric by a Rindler patch characterized by Rob's proper acceleration a0. Because this Rindler approximation breaks down near the extremal limit, we also compute a near-extremal cutoff. Tracing over the inaccessible Rindler wedge yields a mixed Alice-Rob state, from which we evaluate N as a function of the mode frequency ω and the acceleration a0. In all geometries considered, except for one, N increases monotonically with the parameter distinguishing that geometry form the Schwarzschild one. The exception is the Reissner-Nordström metric, for which N exhibits a shallow local minimum at a particular value of the charge. We also find that the Reissner-Nordström metric is the only background for which the negativity falls below that of the Schwarzschild case. Among all cases studied, the Schwarzschild-de Sitter spacetime provides the strongest protection of entanglement. Finally, across all backgrounds, high-frequency modes undergo less degradation than low-frequency modes. These results suggest that entanglement may serve as a useful probe for distinguishing Schwarzschild spacetime from other geometries.
Recent work by Danielson, Satishchandran, and Wald (DSW) has shown that black holes—and, in fact, Killing horizons more generally—impart a fundamental rate of decoherence on all nearby quantum superpositions. The effect can be understood from measurement and causality: An observer (Bob) in the black hole should be able to disturb outside quantum superpositions by measuring their superposed gravitational fields, but since his actions cannot (by causality) have this effect, the superpositions must automatically disturb themselves. DSW calculated the rate of decoherence up to an unknown numerical factor for distant observers in Schwarzschild spacetime, Rindler observers in flat spacetime, and static observers in de Sitter spacetime. Working in electromagnetic and Klein-Gordon analogs, we flesh out and generalize their calculation to derive a general formula for the precise decoherence rate for Killing observers near bifurcate Killing horizons. We evaluate the rate in closed form for an observer at an arbitrary location on the symmetry axis of a Kerr black hole. This fixes the numerical factor in the distant-observer Schwarzschild result, while allowing new exploration of near-horizon and/or near-extremal behavior. In the electromagnetic case we find that the decoherence vanishes entirely in the extremal limit, due to the “black hole Meissner effect” screening the Coulomb field from entering the black hole. This supports the causality picture: Since Bob is unable to measure the field of the outside superposition, no decoherence is necessary—and indeed none occurs. Published by the American Physical Society 2024