Consistent Regularization of Signature-Changing BTZ Black Holes

Fuente: arXiv
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Autore principale: Milani, Farzad
Natura: Preprint
Pubblicazione: 2025
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author Milani, Farzad
author_facet Milani, Farzad
contents Spacetime singularities represent a fundamental challenge in gravitational physics. We present a mathematically consistent framework for signature-changing black holes based on the $(2+1)$-dimensional BTZ metric, where the signature transitions from Lorentzian $(-,+,+)$ to Euclidean $(+,+,+)$ at the horizon. We identify and rectify a critical inconsistency in previous regularization schemes concerning second-order distributional terms $\varepsilon''(r)$, introducing a \emph{modified Hadamard regularization} that respects distribution theory. This produces a vacuum solution free of surface layers and impulsive gravitational waves. Geodesic analysis reveals that radially infalling observers require infinite proper time to reach the horizon, effectively preventing access to the would-be singularity while maintaining finite curvature invariants throughout the spacetime. We further establish the physical robustness of the geometry by demonstrating linear stability against gravitational perturbations, showing that quantum scalar field propagation remains unitary and well-defined across the signature change, and reinterpreting the $r=0$ region as a topological boundary rather than a curvature singularity. Our work establishes atemporality via signature change as a mathematically rigorous mechanism for \emph{singularity avoidance} in black hole spacetimes.
format Preprint
id arxiv_https___arxiv_org_abs_2512_01486
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Consistent Regularization of Signature-Changing BTZ Black Holes
Milani, Farzad
General Relativity and Quantum Cosmology
High Energy Physics - Theory
83C57 . 83C75 . 83C45 . 81T20
Spacetime singularities represent a fundamental challenge in gravitational physics. We present a mathematically consistent framework for signature-changing black holes based on the $(2+1)$-dimensional BTZ metric, where the signature transitions from Lorentzian $(-,+,+)$ to Euclidean $(+,+,+)$ at the horizon. We identify and rectify a critical inconsistency in previous regularization schemes concerning second-order distributional terms $\varepsilon''(r)$, introducing a \emph{modified Hadamard regularization} that respects distribution theory. This produces a vacuum solution free of surface layers and impulsive gravitational waves. Geodesic analysis reveals that radially infalling observers require infinite proper time to reach the horizon, effectively preventing access to the would-be singularity while maintaining finite curvature invariants throughout the spacetime. We further establish the physical robustness of the geometry by demonstrating linear stability against gravitational perturbations, showing that quantum scalar field propagation remains unitary and well-defined across the signature change, and reinterpreting the $r=0$ region as a topological boundary rather than a curvature singularity. Our work establishes atemporality via signature change as a mathematically rigorous mechanism for \emph{singularity avoidance} in black hole spacetimes.
title Consistent Regularization of Signature-Changing BTZ Black Holes
topic General Relativity and Quantum Cosmology
High Energy Physics - Theory
83C57 . 83C75 . 83C45 . 81T20
url https://arxiv.org/abs/2512.01486