arXiv subjects

Terkaa Victor Targema

Publications and source records attributed to Terkaa Victor Targema.

3 recordsLinked to original sources

arXiv2026

On the Maldacena-Shenker-Stanford chaos bound in black hole spacetimes: Saturation, apparent violations, and their geometric origin

Reported violations of the Maldacena-Shenker-Stanford (MSS) chaos bound in black hole spacetimes raise the question of whether they reflect a genuine breakdown, a feature of particular geometries, or a limitation of the probe used to test the bound. We show that the violations are apparent and arise predominantly in the near-extremal regime, where the black hole develops an $AdS_2\times S^2$ throat, the surface gravity becomes parametrically small, while the Lyapunov exponent of an orbit separated from the throat remains nonzero. We establish a geometric criterion governing this behavior and demonstrate its resolution in two complementary ways: a charged-particle construction that localizes an otherwise excluded orbit within the throat and restores exact saturation, and an out-of-time-order correlator (OTOC) calculation in the Jackiw-Teitelboim (JT) throat, which identifies the near-horizon Lyapunov scale and shows why the photon-sphere exponent does not reproduce it when the orbit remains outside the throat. We illustrate the criterion for static and rotating black holes in Einstein, scalar-tensor, and higher-curvature gravity, representative of a broader class of geometries to which it applies. In the absence of external effects that displace the relevant trajectories from the throat, the MSS bound remains respected; the apparent violations instead reflect a geometric decoupling between the probe and the near-horizon region.

hep-th↗

arXiv2026

Geometric effects of torsion on black hole ringdown and shadows in Poincaré gauge gravity

Spacetime torsion provides a natural extension of general relativity and may lead to black hole solutions that differ significantly from their Einsteinian counterparts. We investigate a class of Reissner-Nordström-like black holes in Poincaré gauge gravity, where the effective charge is generated entirely by spacetime torsion instead of an electromagnetic field. Within the physically relevant torsion sector, the spacetime exhibits a single-horizon structure, free from the inner horizons and extremal states characteristic of charged black holes. Using the sixth-order Wentzel-Kramers-Brillouin (WKB) approximation, Leaver's continued-fraction method, and the eikonal correspondence between quasinormal modes and unstable null geodesics, we study scalar perturbations and spin-2 test fields on the torsion-modified background. We find that increasing torsion decreases both the oscillation frequencies and damping rates, leading to longer-lived ringdown signals. We further compare the model predictions with Event Horizon Telescope observations of Sgr A* and M87*, along with representative LIGO-Virgo-KAGRA (LVK) ringdown scales, to derive constraints on the torsion parameter via a profile-$χ^{2}$ analysis supplemented by Monte Carlo sampling. Although the resulting bounds remain consistent with the Schwarzschild limit within current observational uncertainties, our results show that spacetime torsion leaves correlated imprints on both black hole shadows and ringdown observables.

gr-qc↗

arXiv2026

Physical constraints on the Maldacena-Shenker-Stanford chaos-bound in black hole spacetimes

Chaotic motion near black holes has recently been examined through the lens of the Maldacena-Shenker-Stanford (MSS) chaos-bound, but reported violations remain contradictory. A significant source of ambiguity stems from treating the particle angular momentum as an independently adjustable parameter instead of as a quantity fixed by the circular-orbit conditions. We develop a constrained framework in which the angular momentum is determined self-consistently from the geometry. Applied to the charged Kiselev black hole, this framework shows that certain previously reported violations of the chaos bound can be attributed to inconsistent parameter choices rather than to intrinsic curvature effects. By extending the analysis to geometries containing higher-order curvature terms, we find genuine chaos-bound violations at large charge-to-mass ratios, originating from curvature corrections rather than orbital parameters. Our approach, therefore, provides a systematic means to distinguish between parameter-induced (apparent) and curvature-induced (physical) violations in Einstein gravity and its extensions.

hep-th↗