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Delhom, A., Miralles, V., & Peñuelas, A. (2020). Effective interactions in Ricci-Based Gravity below the non-metricity scale. Eur. Phys. J. C, 80(4), 340–14pp.
Abstract: We show how minimally-coupled matter fields of arbitrary spin, when coupled to Ricci-based gravity theories, develop non-trivial effective interactions that can be treated perturbatively only below a characteristic high-energy scale . We then use this interactions to set bounds on the high-energy scale that controls departures of Ricci-Based Gravity theories from General Relativity. Particularly, for Eddington-inspired Born-Infeld gravity we obtain the strong bound vertical bar kappa vertical bar<10(-26)m(5)kg(-1)s(-2).
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Delhom, A., Olmo, G. J., & Orazi, E. (2019). Ricci-Based Gravity theories and their impact on Maxwell and nonlinear electromagnetic models. J. High Energy Phys., 11(11), 149–24pp.
Abstract: We extend the correspondence between metric-affine Ricci-Based Gravity the- ories and General Relativity (GR) to the case in which the matter sector is represented by linear and nonlinear electromagnetic fields. This complements previous studies focused on fluids and scalar fields. We establish the general algorithm that relates the matter fields in the GR and RBG frames and consider some applications. In particular, we find that the so-called Eddington-inspired Born-Infeld gravity theory coupled to Maxwell electromag- netism is in direct correspondence with GR coupled to Born-Infeld electromagnetism. We comment on the potential phenomenological implications of this relation.
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Bejarano, C., Delhom, A., Jimenez-Cano, A., Olmo, G. J., & Rubiera-Garcia, D. (2020). Geometric inequivalence of metric and Palatini formulations of General Relativity. Phys. Lett. B, 802, 135275–4pp.
Abstract: Projective invariance is a symmetry of the Palatini version of General Relativity which is not present in the metric formulation. The fact that the Riemann tensor changes nontrivially under projective transformations implies that, unlike in the usual metric approach, in the Palatini formulation this tensor is subject to a gauge freedom, which allows some ambiguities even in its scalar contractions. In this sense, we show that for the Schwarzschild solution there exists a projective gauge in which the (affine) Kretschmann scalar, K (R beta μnu R alpha beta μnu)-R-alpha, can be set to vanish everywhere. This puts forward that the divergence of curvature scalars may, in some cases, be avoided by a gauge transformation of the connection.
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Delhom, A., Macedo, C. F. B., Olmo, G. J., & Crispino, L. C. B. (2019). Absorption by black hole remnants in metric-affine gravity. Phys. Rev. D, 100(2), 024016–12pp.
Abstract: 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 Born-Infeld gravity. These solutions continuously interpolate between Schwarzschild black holes and naked solitons with wormhole topology. The resulting spectrum is characterized by a series of quasibound states excitations, associated with the existence of a stable photonsphere.
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Delhom, A., Lobo, I. P., Olmo, G. J., & Romero, C. (2019). A generalized Weyl structure with arbitrary non-metricity. Eur. Phys. J. C, 79(10), 878–9pp.
Abstract: A Weyl structure is usually defined by an equivalence class of pairs (g, omega) related by Weyl transformations, which preserve the relation del g = omega circle times g, where g and omega denote the metric tensor and a 1-form field. An equivalent way of defining such a structure is as an equivalence class of conformally related metrics with a unique affine connection Gamma((omega)), which is invariant under Weyl transformations. In a standard Weyl structure, this unique connection is assumed to be torsion-free and have vectorial non-metricity. This second view allows us to present two different generalizations of standard Weyl structures. The first one relies on conformal symmetry while allowing for a general non-metricity tensor, and the other comes from extending the symmetry to arbitrary (disformal) transformations of the metric.
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