Black holes are among the most intriguing objects in nature. They are believed to be fully described by General Relativity (GR), and the astrophysical black holes are expected to belong to the Kerr family, obeying the nohair theorems. Alternative theories of gravity or parameterized deviations of GR allow black hole solutions, which have additional parameters other than mass and angular momentum. We analyze a Schwarzschild-like metric, proposed by Johannsen and Psaltis, characterized by its mass and a deformation parameter. We compute the absorption cross section of massless scalar waves for different values of this deformation parameter and compare it with the corresponding scalar absorption cross section of the Schwarzschild black hole. We also present analytical approximations for the absorption cross section in the high-frequency regime. We check the consistence of our results comparing the numerical and analytical approaches, finding excellent agreement.

We study the correspondence that connects the space of solutions of general relativity (GR) with that of Ricci-based gravity theories (RBGs) of the fðR; QÞ type in the metric-affine formulation, where Q ¼ R ðμνÞ R ðμνÞ . We focus on the case of scalar matter and show that when one considers a free massless scalar in the GR frame, important simplifications arise that allow one to establish the correspondence for arbitrary fðR; QÞ Lagrangian. We particularize the analysis to a quadratic fðR; QÞ theory and use the spherically symmetric, static solution of Jannis-Newman-Winicour as seed to generate new compact objects in our target theory. We find that two different types of solutions emerge, one representing naked singularities and another corresponding to asymmetric wormholes with bounded curvature scalars everywhere. The latter solutions, nonetheless, are geodesically incomplete.

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We study the scattering of light-like geodesics and massless scalar waves by a static Konoplya–Zhidenko black hole, considering the case that the parametrized black hole solution contains a single deformation parameter. By performing a geodesic analysis, we compute the classical differential scattering cross section and probe the influence of the deformation parameter on null trajectories. Moreover, we investigate the propagation of a massless scalar field in the vicinity of the static Konoplya–Zhidenko black hole and use the plane waves formalism to compute the differential scattering cross section. We confront our numerical results in the backward direction with the glory approximation, finding excellent agreement. We compare the results for the deformed black hole with the Schwarzschild case, finding that the additional parameter has an important role in the behavior of the scattering process for moderate-to-high scattering angles.

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