Black holes and gravitational waves in theories extending general relativity

General relativity, together with all its well-tested predictions [1], represents an extremely successful description of gravity. However, there are both theoretical and experimental reasons to believe that this theory should be improved [2]; unfortunately, there are no clear hints on how to do it. Interestingly, the GR's most prominent predictions, such as the existence of black holes or the propagation of gravitational interaction in the form of tiny spacetime ripples, were motivated by simple analytical models, which allowed for a deeper understanding of the theory itself and provided a firm ground for more advanced quantitative studies.

This project aims to follow this approach and study simplified black-hole and radiative spacetimes within modified gravity theories [3,4] such as higher derivative gravities or f(R) theories. The price to pay for the simplification is that we do not directly focus on the quantification of possible observable effects in the first step; however, the benefit we should get is the possibility of analytical calculations uncovering geometrical and physical aspects of various GR modifications in full complexity. In the second step, more realistic scenarios can be investigated using a perturbative approach that extends, for example, the famous Teukolsky procedure [5–7].

[1] Will C M 2014 The Confrontation between General Relativity and Experiment, Liv. Rev. Rel. 17, pp. 4
[2] Stelle K S 1977 Renormalization of higher-derivative quantum gravity, Phys. Rev. D 16, pp. 953
[3] Lü H et al. 2015 Black Holes in Higher Derivative Gravity, Phys. Rev. Lett. 114, 171601
[4] Švarc R et al. 2018 Exact Black Holes in Quadratic Gravity with any Cosmological Constant, Phys. Rev. Lett. 121, 231104
[5] Teukolsky S A 1973 Perturbations of a Rotating Black Hole. I. Fundamental Equations for Gravitational, Electromagnetic, and Neutrino-Field Perturbations, Ast. J. 185, pp. 635
[6] Antoniou G, Gualtieri L, Pani P 2025 Gravitational quasinormal modes of black holes in quadratic gravity, Phys. Rev. D 111, 064059
[7] Knoška Š, Kofroň D, Švarc R 2025 Linear perturbations of Kerr black hole in quadratic gravity, Phys. Rev. D 112, 104058