Channel-Resolved High-Overtone Quasinormal Modes Decode Kasner Scaling inside Black Holes

Abstract

The high-overtone quasinormal-mode spectrum encodes the near-singularity Kasner scaling of black-hole interiors. We show that distinct structures in this spectrum independently determine the temporal and spatial Kasner grades, allowing the corresponding metric exponents to be reconstructed without imposing Kasner constraints or invoking holography. We demonstrate this independent reconstruction at the fixed Kasner point of five-dimensional asymptotically flat Schwarzschild and planar Schwarzschild--AdS$_5$, and then extend it to a continuously varying Gibbons--Maeda black-hole family. The reconstructed exponents satisfy the Kasner relation a posteriori, providing a nontrivial geometric consistency check. More generally, the high-overtone spectrum separates into global spectral data and local algebraic corrections whose fractional powers are fixed by the near-singularity Kasner geometry. These fractional corrections therefore provide a direct spectral probe of the local geometry behind the horizon.