Farhod Nuraliev | Searcharxiv

arXiv2026

Ringdown and greybody signatures of rational regular black holes in non-polynomial gravity

We study the quasinormal mode spectrum and wave-scattering properties of the four-dimensional rational regular black hole recently obtained in non-polynomial (quasi-topological) gravity. Using third-order WKB together with two independent cross-checks a Frobenius--Riccati shooting method and a time-domain evolution we compute the fundamental scalar, electromagnetic, and axial gravitational-type quasinormal frequencies, validating our approach against known Schwarzschild results. We find that as the geometry approaches extremality, its dimensionless ringing frequency is systematically suppressed relative to the Schwarzschild value, a direct and quantifiable imprint of the non-polynomial regularization that we trace, via the photon-sphere correspondence, to the response of the effective potential near the horizon. A Fisher-matrix estimate indicates that this suppression could in principle be resolved by a space-based detector such as LISA for a sufficiently massive and nearby source. We further compute, for the first time, the axial gravitational-type ringdown spectrum of this geometry using the Regge--Wheeler master equation, while noting that a full stability analysis of the underlying gravity theory remains an open problem requiring the linearized field equations of the modified action. Finally, we examine the greybody transmission factors across spins $s=0,1,2$ and show that they follow the same systematic ordering and near-extremal enhancement as the ringing-frequency suppression, pointing to a common physical origin. Together, these results give one of the first quantitative characterizations of the observational signatures and the remaining open theoretical questions of a regular black hole in modified gravity.

gr-qc↗

arXiv2026

Probing black holes surrounded by Dust field in Quantum Fluctuation Modified Gravity with twin-peak QPOs

We study a static, spherically symmetric black hole solution surrounded by a dust field within quantum fluctuation modified gravity, in which the quantum-fluctuation parameter $α$ and the dust-field strength parameter $K$. The horizon structure reveals the two parameters acting in opposite directions: strengthening $K$ draws the inner and outer horizons together until they merge into a single extremal horizon, while a larger $α$ restores the Schwarzschild limit; the same opposing trend extends to the effective potential and the characteristic circular-orbit radii -- the innermost stable circular orbit, the marginally bound orbit, and the marginal circular orbit -- which shift inward with $K$ and outward with $α$, and to the Keplerian and radial epicyclic frequencies of massive test particles. From these frequencies we build three twin-peak quasi-periodic oscillation models -- relativistic precession, warped-disk, and epicyclic-resonance -- along with their $3{:}2$, $4{:}3$, and $5{:}4$ resonance radii, all following the same $K$-$α$ trend. Testing all three models against twin-peak QPO data from two stellar-mass (GRO~J1655$-$40, XTE~J1550$-$564) and two intermediate-mass (M82~X$-$1, NGC~1313~X$-$1) sources through a Markov Chain Monte Carlo analysis places best-fit constraints, at the $2σ$ level, of $K\in(0,0.5)$ and $α\in(0.3,0.6)$ across all sources and models.

gr-qc↗