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Olmo, G. J., Rubiera-Garcia, D., & Saez-Chillon Gomez, D. (2022). New light rings from multiple critical curves as observational signatures of black hole mimickers. Phys. Lett. B, 829, 137045–5pp.
Abstract: We argue that the appearance of additional light rings in a shadow observation – beyond the infinite sequence of exponentially demagnified self-similar rings foreseen in the Kerr solution – would make a compelling case for the existence of black hole mimickers having multiple critical curves. We support this claim by discussing three different scenarios of spherically symmetric wormhole geometries having two such critical curves, and explicitly work out the optical appearance of one such object when surrounded by an optically and geometrically thin accretion disk.
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Olmo, G. J., & Rubiera-Garcia, D. (2022). Some recent results on Ricci-based gravity theories. Int. J. Mod. Phys. D, 31, 2240012–15pp.
Abstract: In this paper, metric-afline theories in which the gravity Lagrangian is built using (projectively invariant) contractions of the Ricci tensor with itself and with the metric (Ricci-based gravity theories, or RBGs for short) are reviewed. The goal is to provide a contextualized and coherent presentation of some recent results. In particular, we focus on the correspondence that exists between the field equations of these theories and those of general relativity, and comment on how this can be used to build new solutions of physical interest. We also discuss the formalism of junction conditions in the f (R) case, and provide a brief summary on current experimental and observational bounds on model parameters.
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