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Bejarano, C., Lobo, F. S. N., Olmo, G. J., & Rubiera-Garcia, D. (2017). Palatini wormholes and energy conditions from the prism of general relativity. Eur. Phys. J. C, 77(11), 776–13pp.
Abstract: Wormholes are hypothetical shortcuts in space-time that in general relativity unavoidably violate all of the pointwise energy conditions. In this paper, we consider several wormhole spacetimes that, as opposed to the standard designer procedure frequently employed in the literature, arise directly from gravitational actions including additional terms resulting from contractions of the Ricci tensor with the metric, and which are formulated assuming independence between metric and connection (Palatini approach). We reinterpret such wormhole solutions under the prism of General Relativity and study the matter sources that thread them. We discuss the size of violation of the energy conditions in different cases and how this is related to the same spacetimes when viewed from the modified gravity side.
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Olmo, G. J., Rubiera-Garcia, D., & Sanchez-Puente, A. (2016). Classical resolution of black hole singularities via wormholes. Eur. Phys. J. C, 76(3), 143–6pp.
Abstract: In certain extensions of General Relativity, wormholes generated by spherically symmetric electric fields can resolve black hole singularities without necessarily removing curvature divergences. This is shown by studying geodesic completeness, the behavior of time-like congruences going through the divergent region, and by means of scattering of waves off the wormhole. This provides an example of the logical independence between curvature divergences and space-time singularities, concepts very often identified with each other in the literature.
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Bazeia, D., Losano, L., Menezes, R., Olmo, G. J., & Rubiera-Garcia, D. (2015). Thick brane in f(R) gravity with Palatini dynamics. Eur. Phys. J. C, 75, 569–10pp.
Abstract: This work deals with modified gravity in five dimensional spacetime. We study a thick Palatini f(R) brane, that is, a braneworld scenario described by an anti-de Sitter warped geometry with a single extra dimension of infinite extent, sourced by real scalar field under the Palatini approach, where the metric and the connection are regarded as independent degrees of freedom. We consider a first-order framework which we use to provide exact solutions for the scalar field and warp factor. We also investigate a perturbative scenario such that the Palatini approach is implemented through a Lagrangian f(R)=R+ϵR^n, where the small parameter ϵ controls the deviation from the standard thick brane case.
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Olmo, G. J., Rubiera-Garcia, D., & Sanchis-Alepuz, H. (2014). Geonic black holes and remnants in Eddington-inspired Born-Infeld gravity. Eur. Phys. J. C, 74(3), 2804–6pp.
Abstract: We show that electrically charged solutions within the Eddington-inspired Born-Infeld theory of gravity replace the central singularity by a wormhole supported by the electric field. As a result, the total energy associated with the electric field is finite and similar to that found in the Born-Infeld electromagnetic theory. When a certain charge-to-mass ratio is satisfied, in the lowest part of the mass and charge spectrum the event horizon disappears, yielding stable remnants. We argue that quantum effects in the matter sector can lower the mass of these remnants from the Planck scale down to the TeV scale.
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Lobo, F. S. N., Olmo, G. J., & Rubiera-Garcia, D. (2014). Microscopic wormholes and the geometry of entanglement. Eur. Phys. J. C, 74(6), 2924–5pp.
Abstract: It has recently been suggested that Einstein-Rosen (ER) bridges can be interpreted as maximally entangled states of two black holes that form a complex Einstein-Podolsky-Rosen (EPR) pair. This relationship has been dubbed as the correlation. In this work, we consider the latter conjecture in the context of quadratic Palatini theory. An important result, which stems from the underlying assumptions as regards the geometry on which the theory is constructed, is the fact that all the charged solutions of the quadratic Palatini theory possess a wormhole structure. Our results show that spacetime may have a foam-like microstructure with wormholes generated by fluctuations of the quantum vacuum. This involves the spontaneous creation/annihilation of entangled particle-antiparticle pairs, existing in a maximally entangled state connected by a non-traversable wormhole. Since the particles are produced from the vacuum and therefore exist in a singlet state, they are necessarily entangled with one another. This gives further support to the claim.
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