
Afonso, V. I., Bejarano, C., Ferraro, R., & Olmo, G. J. (2022). Determinantal BornInfeld coupling of gravity and electromagnetism. Phys. Rev. D, 105(8), 084067–11pp.
Abstract: We study a BornInfeld inspired model of gravity and electromagnetism in which both types of fields are treated on an equal footing via a determinantal approach in a metricaft me formulation. Though this formulation is a priori in conflict with the postulates of metric theories of gravity, we find that the resulting equations can also be obtained from an action combining the EinsteinHilbert action with a minimally coupled nonlinear electrodynamics. As an example, the dynamics is solved for the charged static black hole.



Afonso, V. I., MoraPerez, G., Olmo, G. J., Orazi, E., & RubieraGarcia, D. (2022). An infinite class of exact rotating black hole metrics of modified gravity. J. Cosmol. Astropart. Phys., 03(3), 052–14pp.
Abstract: We build an infinite class of exact axisymmetric solutions of a metricaffine gravity theory, namely, Eddingtoninspired BornInfeld gravity, coupled to an anisotropic fluid as a matter source. The solutiongenerating method employed is not unique of this theory but can be extended to other RicciBased Gravity theories (RBGs), a class of theories built out of contractions of the Ricci tensor with the metric. This method exploits a correspondence between the space of solutions of General Relativity and that of RBGs, and is independent of the symmetries of the problem. For the particular case in which the fluid is identified with nonlinear electromagnetic fields we explicitly derive the corresponding axisymmetric solutions. Finally, we use this result to work out the counterpart of the KerrNewman black hole when Maxwell electrodynamics is set on the metricaffine side. Our results open up an exciting new avenue for testing new gravitational phenomenology in the fields of gravitational waves and shadows out of rotating black holes.



Afonso, V. I., Olmo, G. J., Orazi, E., & RubieraGarcia, D. (2019). New scalar compact objects in Riccibased gravity theories. J. Cosmol. Astropart. Phys., 12(12), 044–20pp.
Abstract: Taking advantage of a previously developed method, which allows to map solutions of General Relativity into a broad family of theories of gravity based on the Ricci tensor (Riccibased gravities), we find new exact analytical scalar field solutions by mapping the freefield static, spherically symmetric solution of General Relativity (GR) into quadratic f(R) gravity and the Eddingtoninspired BornInfeld gravity. The obtained solutions have some distinctive feature below the wouldbe Schwarzschild radius of a configuration with the same mass, though in this case no horizon is present. The compact objects found include wormholes, compact balls, shells of energy with no interior, and a new kind of object which acts as a kind of wormhole membrane. The latter object has Euclidean topology but connects antipodal points of its surface by transferring particles and null rays across its interior in virtually zero affine time. We point out the relevance of these results regarding the existence of compact scalar field objects beyond General Relativity that may effectively act as black hole mimickers.



Afonso, V. I., Olmo, G. J., Orazi, E., & RubieraGarcia, D. (2019). Correspondence between modified gravity and general relativity with scalar fields. Phys. Rev. D, 99(4), 044040–15pp.
Abstract: We describe a novel procedure to map the field equations of nonlinear Riccibased metricaffine theories of gravity, coupled to scalar matter described by a given Lagrangian, into the field equations of general relativity coupled to a different scalar field Lagrangian. Our analysis considers examples with a single and N real scalar fields, described either by canonical Lagrangians or by generalized functions of the kinetic and potential terms. In particular, we consider several explicit examples involving foRthorn theories and the Eddingtoninspired BornInfeld gravity model, coupled to different scalar field Lagrangians. We show how the nonlinearities of the gravitational sector of these theories can be traded to nonlinearities in the matter fields and how the procedure allows to find new solutions on both sides of the correspondence. The potential of this procedure for applications of scalar field models in astrophysical and cosmological scenarios is highlighted.



Afonso, V. I., Olmo, G. J., Orazi, E., & RubieraGarcia, D. (2018). Mapping nonlinear gravity into General Relativity with nonlinear electrodynamics. Eur. Phys. J. C, 78(10), 866–11pp.
Abstract: We show that families of nonlinear gravity theories formulated in a metricaffine approach and coupled to a nonlinear theory of electrodynamics can be mapped into general relativity (GR) coupled to another nonlinear theory of electrodynamics. This allows to generate solutions of the former from those of the latter using purely algebraic transformations. This correspondence is explicitly illustrated with the Eddingtoninspired BornInfeld theory of gravity, for which we consider a family of nonlinear electrodynamics and show that, under the map, preserve their algebraic structure. For the particular case of Maxwell electrodynamics coupled to BornInfeld gravity we find, via this correspondence, a BornInfeldtype nonlinear electrodynamics on the GR side. Solving the spherically symmetric electrovacuum case for the latter, we show how the map provides directly the right solutions for the former. This procedure opens a new door to explore astrophysical and cosmological scenarios in nonlinear gravity theories by exploiting the full power of the analytical and numerical methods developed within the framework of GR.



Afonso, V. I., Olmo, G. J., & RubieraGarcia, D. (2018). Mapping Riccibased theories of gravity Into general relativity. Phys. Rev. D, 97(2), 021503–6pp.
Abstract: We show that the space of solutions of a wide class of Riccibased metricaffine theories of gravity can be put into correspondence with the space of solutions of general relativity (GR). This allows us to use wellestablished methods and results from GR to explore new gravitational physics beyond it.



Afonso, V. I., Olmo, G. J., & RubieraGarcia, D. (2017). Scalar geons in BornInfeld gravity. J. Cosmol. Astropart. Phys., 08(8), 031–35pp.
Abstract: The existence of static, spherically symmetric, selfgravitating scalar field solutions in the context of BornInfeld gravity is explored. Upon a combination of analytical approximations and numerical methods, the equations for a free scalar field (without a potential term) are solved, verifying that the solutions recover the predictions of General Relativity far from the center but finding important new effects in the central regions. We find two classes of objects depending on the ratio between the Schwarzschild radius and a length scale associated to the BornInfeld theory: massive solutions have a wormhole structure, with their throat at r = 2 M, while for the lighter configurations the topology is Euclidean. The total energy density of these solutions exhibits a solitonic profile with a maximum peaked away from the center, and located at the throat whenever a wormhole exists. The geodesic structure and curvature invariants are analyzed for the various configurations considered.



Agullo, I., NavarroSalas, J., Olmo, G. J., & Parker, L. (2011). Remarks on the renormalization of primordial cosmological perturbations. Phys. Rev. D, 84(10), 107304–5pp.
Abstract: We briefly review the need to perform renormalization of inflationary perturbations to properly work out the physical power spectra. We also summarize the basis of (momentumspace) renormalization in curved spacetime and address several misconceptions found in recent literature on this subject.



Agullo, I., NavarroSalas, J., Olmo, G. J., & Parker, L. (2010). Acceleration radiation, transition probabilities and transPlanckian physics. New J. Phys., 12, 095017–18pp.
Abstract: An important question in the derivation of the acceleration radiation, which also arises in Hawking's derivation of black hole radiance, is the need to invoke transPlanckian physics in describing the creation of quanta. We point out that this issue can be further clarified by reconsidering the analysis in terms of particle detectors, transition probabilities and local twopoint functions. By writing down separate expressions for the spontaneousand inducedtransition probabilities of a uniformly accelerated detector, we show that the bulk of the effect comes from the natural (nontransPlanckian) scale of the problem, which largely diminishes the importance of the transPlanckian sector. This is so, at least, when transPlanckian physics is defined in a Lorentzinvariant way. This analysis also suggests how one can define and estimate the role of transPlanckian physics in the Hawking effect itself.



Agullo, I., NavarroSalas, J., Olmo, G. J., & Parker, L. (2010). Reply to "Comment on 'Insensitivity of Hawking radiation to an invariant Planckscale cutoff' ''. Phys. Rev. D, 81(10), 108502–3pp.
Abstract: We clarify the relationship between the conclusions of the previous Comment of A. Helfer [A. Helfer, preceding Comment, Phys. Rev. D 81, 108501 (2010)] and that of our Brief Report [I. Agullo, J. NavarroSalas, G. J. Olmo, and L. Parker, Phys. Rev. D 80, 047503 (2009).].

