Simon Knoska | Searcharxiv

arXiv2026

Exact Bachian singularity in quadratic gravity

For specifically coupled values of the quadratic gravity parameters, we present a fully explicit static spherically symmetric solution. It contains the central singularity surrounded by the black-hole or the cosmological horizon for the negative or positive cosmological parameter, respectively. This spacetime, thus, belongs to the already analyzed classes of solutions expressed in terms of the Frobenius expansions, continuous fractions, or numerical simulations; however, it has not been explicitly identified before. The purpose of the presented highly-constrained somehow unphysical model is to reveal a global geometric picture that may occur in spherical spacetimes within quadratic gravity, which is typically hidden in more general approximative solutions. At the same time, it can serve as a solid benchmark for evaluating the accuracy of the methods employed to obtain such solutions.

gr-qc↗

arXiv2025

Linear perturbations of Kerr black hole in quadratic gravity

Employing the Newman-Penrose formalism and following the classic Teukolsky-like approach, we linearise the field equations of quadratic gravity on the Kerr background and combine them with the linearised Ricci and Bianch identities. This leads to constraints on linear perturbations of the Kerr spacetime in quadratic gravity. The resulting differential equations are decoupled in such a way that only the Ricci tensor perturbations need to be found on the Kerr background in order to fully determine the solution. The results are illustrated in the simple non-trivial cases of the Schwarzschild and Minkowski geometries.

gr-qc↗