Motivated by recent work on the Modified Maxwell (ModMax) black holes [Phys Lett B
10.1016/j. physletb. 2020.136011], which are invariant in duality rotations and conformal …

The superradiant instability can lead to the generation of extremely dense axion clouds
around rotating black holes. We show that, despite the long lifetime of the QCD axion with …

Using numerical methods, we investigate the absorption properties of a family of
nonsingular solutions which arise in different metric-affine theories, such as quadratic and …

The tidal response of a compact object is a key gravitational-wave observable encoding
information about its interior. This link is subtle due to the nonlinearities of general relativity …

Axions can be stimulated to decay into photons by ambient photons of the right frequency or
by photons from the decay of neighboring axions. If the axion density is high enough, the …

We investigate the scalar absorption spectrum of wormhole solutions constructed via the
recently developed thin-shell formalism for Palatini f (R) gravity. Such wormholes come from …

Regular black holes (RBHs)—geometries free from curvature singularities—arise naturally
in theories of nonlinear electrodynamics. Here we study the absorption and superradiant …

The propagation of gravitational waves can be described in terms of null geodesics by using
the geometrical optics approximation. However, at large but finite frequencies the …

We consider the propagation of a generic scalar field around a rotating and charged black
hole. Using the partial wave method, we find, numerically, the total and partial absorption …

The geometrical-optics expansion reduces the problem of solving wave equations to one of
the solving transport equations along rays. Here, we consider scalar, electromagnetic and …