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Lobo, F. S. N., Martinez-Asencio, J., Olmo, G. J., & Rubiera-Garcia, D. (2014). Planck scale physics and topology change through an exactly solvable model. Phys. Lett. B, 731, 163–167.
Abstract: We consider the collapse of a charged radiation fluid in a Planck-suppressed quadratic extension of General Relativity (GR) formulated A la Palatini. We obtain exact analytical solutions that extend the charged Vaidya-type solution of GR, which allows to explore in detail new physics at the Planck scale. Starting from Minkowski space, we find that the collapsing fluid generates wormholes supported by the electric field. We discuss the relevance of our findings in relation to the quantum foam structure of space-time and the meaning of curvature divergences in this theory.
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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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Bazeia, D., Losano, L., Olmo, G. J., & Rubiera-Garcia, D. (2014). Black holes in five-dimensional Palatini f(R) gravity and implications for the AdS/CFT correspondence. Phys. Rev. D, 90(4), 044011–8pp.
Abstract: We show that theories having second-order field equations in the context of higher-dimensional modified gravity are not restricted to the family of Lovelock Lagrangians, but can also be obtained if no a priori assumption on the relation between the metric and affine structures of space-time is made (the Palatini approach). We illustrate this fact by considering the case of Palatini f(R) gravities in five dimensions. Our results provide an alternative avenue to explore new domains of the AdS/CFT correspondence without resorting to ad hoc quasitopological constructions.
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Odintsov, S. D., Olmo, G. J., & Rubiera-Garcia, D. (2014). Born-Infeld gravity and its functional extensions. Phys. Rev. D, 90(4), 044003–8pp.
Abstract: We investigate the dynamics of a family of functional extensions of the (Eddington-inspired) Born-Infeld gravity theory, constructed with the inverse of the metric and the Ricci tensor. We provide a generic formal solution for the connection and an Einstein-like representation for the metric field equations of this family of theories. For particular cases we consider applications to the early-time cosmology and find that nonsingular universes with a cosmic bounce are very generic and robust solutions.
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Lobo, F. S. N., Martinez-Asencio, J., Olmo, G. J., & Rubiera-Garcia, D. (2014). Dynamical generation of wormholes with charged fluids in quadratic Palatini gravity. Phys. Rev. D, 90(2), 024033–15pp.
Abstract: The dynamical generation of wormholes within an extension of General Relativity (GR) containing (Planck's scale-suppressed) Ricci-squared terms is considered. The theory is formulated assuming the metric and connection to be independent (Palatini formalism) and is probed using a charged null fluid as a matter source. This has the following effect: starting from Minkowski space, when the flux is active the metric becomes a charged Vaidya-type one, and once the flux is switched off the metric settles down into a static configuration such that far from the Planck scale the geometry is virtually indistinguishable from that of the standard Reissner-Nordstrom solution of GR. However, the innermost region undergoes significant changes, as the GR singularity is generically replaced by a wormhole structure. Such a structure becomes completely regular for a certain charge-to-mass ratio. Moreover, the nontrivial topology of the wormhole allows us to define a charge in terms of lines of force trapped in the topology such that the density of lines flowing across the wormhole throat becomes a universal constant. In light of our results, we comment on the physical significance of curvature divergences in this theory and the topology change issue, which support the view that space-time could have a foamlike microstructure pervaded by wormholes generated by quantum gravitational effects.
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