Publicaciones Recientes | Menu principal
|
Aquí podrá encontrar detalladas las publicaciones de los miembros del grupo durante el último año. Se incluyen tanto los artículos regulares como las contribuciones a conferencias. En algunos casos se ha incluído un enlace a la versión publicada del artículo. |
Publicaciones 2012
Title: Open Questions in Cosmology.
Author: Gonzalo J. Olmo (Editor).
Reference: Hard cover, 334 pages, Publisher: InTech, Published: November 12, 2012. ISBN 978-953-51-0880-1.
Abstract: In the last years we have witnessed how the field of Cosmology has experienced a metamorphosis. From being essentially the search for three numbers (the expansion rate, the deceleration parameter, and the cosmological constant), it has become a precision science. This scientific discipline is determined to unravel the most minute details of the elementary processes that took place during the most primitive stages of the Universe and also of the mechanisms driving the cosmic expansion and the growth of structures at the largest scales. To achieve these goals one needs not only the development of new experimental and observational techniques but also a deep understanding of the underlying theoretical frameworks. This book gathers the work of leading experts in these fields and provides a broad view of some of the most relevant open questions faced by Cosmology at the beginning of the twenty-first century.
|
Title: Introduction to Palatini theories of gravity and nonsingular cosmologies. Authors: Gonzalo J. Olmo Journal-ref: Chapter of the book Open Questions in Cosmology , edited by Gonzalo J. Olmo. InTech Publishing, Rijeka, Croatia, (2012), ISBN 978-953-51-0880-1.. Abstract: These notes are a summary of lectures given at the Instituto de Astronomia of the Universidad Nacional Autonoma de Mexico (UNAM), the Dipartimento di Fisica of the Universita degli studi di Salerno (Italy), and the Instituto de Fisica Corpuscular of the Universitat de Valencia (Spain) during the year 2012. Basic mathematical aspects of Palatini theories of gravity, which are constructed assuming that metric and connection are independent geometrical entities, are briefly introduced and discussed, and followed by a detailed derivation of the field equations of some rather general Lagrangian theories. Applications to the early universe are considered paying special attention to the avoidance of the big bang singularity. The analysis of non-singular cosmologies carried out in arXiv:1005.4136 [gr-qc] is extended to include several perfect fluids. |
|
Title: The virial theorem and the dark matter problem in hybrid metric-Palatini gravity. Authors: S. Capozziello, T. Harko, T. S. Koivisto, F. S. N. Lobo, Gonzalo J. Olmo Journal-ref: arXiv. Abstract: Hybrid metric-Palatini gravity is a recently proposed theory, consisting of the superposition of the metric Einstein-Hilbert Lagrangian with an $f(\cal R)$ term constructed \`{a} la Palatini. The theory predicts the existence of a long-range scalar field, which passes the Solar System observational constraints, even if the scalar field is very light, and modifies the cosmological and galactic dynamics. Thus, the theory opens new possibilities to approach, in the same theoretical framework, the problems of both dark energy and dark matter. In this work, we consider the generalized virial theorem in the scalar-tensor representation of the hybrid metric-Palatini gravity. More specifically, taking into account the relativistic collisionless Boltzmann equation, we show that the supplementary geometric terms in the gravitational field equations provide an effective contribution to the gravitational potential energy. We show that the total virial mass is proportional to the effective mass associated with the new terms generated by the effective scalar field, and the baryonic mass. This shows that the geometric origin in the generalized virial theorem may account for the well-known virial theorem mass discrepancy in clusters of galaxies. In addition to this, we also consider astrophysical applications of the model and show that the model predicts that the mass associated to the scalar field and its effects extend beyond the virial radius of the clusters of galaxies. In the context of the galaxy cluster velocity dispersion profiles predicted by the hybrid metric-Palatini model, the generalized virial theorem can be an efficient tool in observationally testing the viability of this class of generalized gravity models. Thus, hybrid metric-Palatini gravity provides an effective alternative to the dark matter paradigm of present day cosmology and astrophysics. |
|
Title: An Extension of the Quantum Theory of Cosmological Perturbations to the Planck Era. Authors: Ivan Agullo, Abhay Ashtekar, William Nelson. Journal-ref: Abstract: Cosmological perturbations are generally described by quantum fields on (curved but) classical space-times. While this strategy has a large domain of validity, it can not be justified in the quantum gravity era where curvature and matter densities are of Planck scale. Using techniques from loop quantum gravity, the standard theory of cosmological perturbations is extended to overcome this limitation. The new framework sharpens conceptual issues by distinguishing between the true and apparent trans-Planckian difficulties and provides sufficient conditions under which the true difficulties can be overcome within a quantum gravity theory. In a companion paper, this framework is applied to the standard inflationary model, with interesting implications to theory as well as observations. . |
|
Title: Stellar Structure Equations in Extended Palatini Gravity Authors: Gonzalo J. Olmo, Helios Sanchis-Alepuz, Swapnil Tripathi Journal-ref: Abstract: We consider static spherically symmetric stellar configurations in Palatini theories of gravity in which the Lagrangian is an unspecified function of the form f(R,R_{\mu\nu}R^{\mu\nu}). We obtain the Tolman-Oppenheimer-Volkov equations corresponding to this class of theories and show that they recover those of f(R) theories and General Relativity in the appropriate limits. We show that the exterior vacuum solutions are of Schwarzschild-de Sitter type and comment on the possible expected modifications, as compared to GR, of the interior solutions. |
|
Title: Static Spherically Symmetric Solutions in Extended Palatini Gravity. Authors: Gonzalo J. Olmo, Helios Sanchis-Alepuz, Swapnil Tripathi Journal-ref: Abstract: We consider static spherically symmetric stellar configurations in Palatini theories of gravity in which the Lagrangian is an unspecified function of the form f(R,R_{\mu\nu}R^{\mu\nu}). We obtain the Tolman-Oppenheimer-Volkov equations corresponding to this class of theories and show that they recover those of f(R) theories and General Relativity in the appropriate limits. We compute exterior vacuum solutions and comment on the possible expected modifications, as compared to GR, of the interior solutions. |
|
Title: Wormholes supported by hybrid metric-Palatini gravity. Authors: S. Capozziello, T. Harko, T. S. Koivisto, F. S. N. Lobo, Gonzalo J. Olmo Journal-ref: Phys.Rev.D86:127504,2012. Abstract: Recently, a modified theory of gravity was presented, which consists of the superposition of the metric Einstein-Hilbert Lagrangian with an $f(\cal R)$ term constructed \`{a} la Palatini. The theory possesses extremely interesting features such as predicting the existence of a long-range scalar field, that explains the late-time cosmic acceleration and passes the local tests, even in the presence of a light scalar field. In this brief report, we consider the possibility that wormholes are supported by this hybrid metric-Palatini gravitational theory. We present here the general conditions for wormhole solutions according to the null energy conditions at the throat and find specific examples. In the first solution, we specify the redshift function, the scalar field and choose the potential that simplifies the modified Klein-Gordon equation. This solution is not asymptotically flat and needs to be matched to a vacuum solution. In the second example, by adequately specifying the metric functions and choosing the scalar field, we find an asymptotically flat spacetime. |
|
Title: Black hole formation from a null fluid in extended Palatini gravity. Authors: J. Martinez-Asencio, Gonzalo J. Olmo, D. Rubiera-Garcia Journal-ref: Phys.Rev. D86 (2012) 104010. Abstract: We study the formation and perturbation of black holes by null fluxes of neutral matter in a quadratic extension of General Relativity formulated a la Palatini. Working in a spherically symmetric space-time, we obtain an exact analytical solution for the metric that extends the usual Vaidya-type solution to this type of theories. We find that the resulting space-time is formally that of a Reissner-Nordstrom black hole but with an effective charge term carrying the wrong sign in front of it. This effective charge is directly related to the luminosity function of the radiation stream. When the ingoing flux vanishes, the charge term disappears and the space-time relaxes to that of a Schwarzschild black hole. We provide two examples that illustrate the formation of a black hole from Minkowski space and the perturbation by a finite pulse of radiation of an existing Schwarzschild black hole. |
|
Title: Cosmology of hybrid metric-Palatini f(X)-gravity. Authors: Salvatore Capozziello, Tiberiu Harko, Tomi S. Koivisto, Francisco S.N. Lobo, Gonzalo J. Olmo Abstract: A new class of modified theories of gravity, consisting of the superposition of the metric Einstein-Hilbert Lagrangian with an $f(\cal R)$ term constructed \`{a} la Palatini was proposed recently. The dynamically equivalent scalar-tensor representation of the model was also formulated, and it was shown that even if the scalar field is very light, the theory passes the Solar System observational constraints. Therefore the model predicts the existence of a long-range scalar field, modifying the cosmological and galactic dynamics. An explicit model that passes the local tests and leads to cosmic acceleration was also obtained. In the present work, it is shown that the theory can be also formulated in terms of the quantity $X\equiv \kappa^2 T+R$, where T and R are the traces of the stress-energy and Ricci tensors, respectively. The variable X represents the deviation with respect to the field equation trace of general relativity. The cosmological applications of this hybrid metric-Palatini gravitational theory are also explored, and cosmological solutions coming from the scalar-tensor representation of f(X)-gravity are presented. Criteria to obtain cosmic acceleration are discussed and the field equations are analyzed as a dynamical system. Several classes of dynamical cosmological solutions, depending on the functional form of the effective scalar field potential, describing both accelerating and decelerating Universes are explicitly obtained. Furthermore, the cosmological perturbation equations are derived and applied to uncover the nature of the propagating scalar degree of freedom and the signatures these models predict in the large-scale structure. |
|
Title: Black holes with electric charge in Palatini theories of gravity. Authors: Gonzalo J. Olmo, D. Rubiera-Garcia. Journal-ref: AIP Conf. Proc. 1458, pp. 511-514. Abstract: We discuss the procedure of solving the field equations of Palatini f(R) and f(R,Q) theories coupled to an arbitrary nonlinear theory of electrodynamics as the matter source in spherically symmetric, static backgrounds. We provide a formal analytical solution for the metric in all such black hole spacetimes. |
|
Title: A Quantum Gravity Extension of the Inflationary Scenario. Authors: Ivan Agullo, Abhay Ashtekar, William Nelson. Journal-ref: Phys. Rev. Lett. 109, 251301 (2012). Abstract: Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the paradigm is extended to a self-consistent theory from the Planck scale to the onset of slow roll inflation, covering some 11 orders of magnitude in energy density and curvature. This pre-inflationary dynamics also opens a small window for novel effects, e.g. a source for non-Gaussianities, which could extend the reach of cosmological observations to the deep Planck regime of the early universe. |
|
Title: Reissner-Nordström black holes in extended Palatini theories. Authors: Gonzalo J. Olmo Journal-ref: Phys.Rev. D86 (2012) 044014. Abstract: We study static, spherically symmetric solutions with an electric field in an extension of general relativity (GR) containing a Ricci-squared term and formulated in the Palatini formalism. We find that all the solutions present a central core whose area is proportional to the Planck area times the number of charges. Far from the core, curvature invariants quickly tend to those of the usual Reissner-Nordstr\"om solution, though the structure of horizons may be different. In fact, besides the structures found in the Reissner-Nordstr\"om solution of GR, we find black hole solutions with just one nondegenerate horizon (Schwarzschild-like), and nonsingular black holes and naked cores. The charge-to-mass ratio of the nonsingular solutions implies that the core matter density is independent of the specific amounts of charge and mass and of order the Planck density. We discuss the physical implications of these results for astrophysical and microscopic black holes, construct the Penrose diagrams of some illustrative cases, and show that the maximal analytical extension of the nonsingular solutions implies a bounce of the radial coordinate. |
|
Title: Cosmology in Palatini theories of gravity. Authors: Gonzalo J. Olmo Journal-ref: AIP Conf. Proc. 1458 (2011), 222-237. Abstract: We discuss recent results on the cosmology of extended theories of gravity formulated in the Palatini approach, i.e., assuming that metric and connection are independent fields. In particular, we focus on the attempts to explain the cosmic speedup with f(R) theories and on models that avoid the big bang singularity. The field equations for gravity Lagrangians of the form f(g_{\mu\nu},{R^\alpha}_{\beta\mu\nu}) (including torsion) are explicitly derived and discussed. |
|
Title: Nonsingular charged black holes à la Palatini. Authors: Gonzalo J. Olmo, Diego Rubiera-Garcia Journal-ref: Int.J.Mod.Phys. D21 (2012) 1250067. Abstract: We argue that the quantum nature of matter and gravity should lead to a discretization of the allowed states of the matter confined in the interior of black holes. To support and illustrate this idea, we consider a quadratic extension of General Relativity formulated \`{a} la Palatini and show that nonrotating, electrically charged black holes develop a compact core at the Planck density which is nonsingular if the mass spectrum satisfies a certain discreteness condition. We also find that the area of the core is proportional to the number of charges times the Planck area. |
|
Title: Birkhoff's theorem and perturbations in $f(R)$ theories Authors: Gonzalo J. Olmo Journal-ref: Annalen Phys. 524 (2012) 87-88. Abstract: Invited contribution to Annalen der Physik (Expert Opinion). |
|
Title: Hawking radiation of massive modes and undulations. Authors: Antonin Coutant, Alessandro Fabbri, Renaud Parentani, Roberto Balbinot, Paul Anderson. Journal-ref: Phys. Rev. D 86, 064022 (2012) . Abstract: We compute the analogue Hawking radiation for modes which posses a small wave vector perpendicular to the horizon. For low frequencies, the resulting mass term induces a total reflection. This generates an extra mode mixing that occurs in the supersonic region, which cancels out the infrared divergence of the near horizon spectrum. As a result, the amplitude of the undulation (0-frequency wave with macroscopic amplitude) emitted in white hole flows now saturates at the linear level, unlike what was recently found in the massless case. In addition, we point out that the mass introduces a new type of undulation which is produced in black hole flows, and which is well described in the hydrodynamical regime. |
|
Title: Large non-Gaussian Halo Bias from Single Field Inflation. Authors: Ivan Agullo, Sarah Shandera. Journal-ref: JCAP09(2012)007 . Abstract: We calculate Large Scale Structure observables for non-Gaussianity arising from non-Bunch-Davies initial states in single field inflation. These scenarios can have substantial primordial non-Gaussianity from squeezed (but observable) momentum configurations. They generate a term in the halo bias that may be more strongly scale-dependent than the contribution from the local ansatz. We also discuss theoretical considerations required to generate an observable signature. |
|
Title: Perturbations in loop quantum cosmology. Authors: Ivan Agullo, Abhay Ashtekar, William Nelson. Journal-ref: ICGC (2011) Goa Conference proceedings . Abstract: The era of precision cosmology has allowed us to accurately determine many important cosmological parameters, in particular via the CMB. Confronting Loop Quantum Cosmology with these observations provides us with a powerful test of the theory. For this to be possible we need a detailed understanding of the generation and evolution of inhomogeneous perturbations during the early, Quantum Gravity, phase of the universe. Here we describe how Loop Quantum Cosmology provides a completion of the inflationary paradigm, that is consistent with the observed power spectra of the CMB. |
|
Title: Prime numbers, quantum field theory and the Goldbach conjecture. Authors: Miguel-Angel Sanchis-Lozano, J. Fernando Barbero G., Jose Navarro-Salas Journal-ref: Int.J.Mod.Phys. A27 (2012) 1250136 . Abstract: Motivated by the Goldbach conjecture in Number Theory and the abelian bosonization mechanism on a cylindrical two-dimensional spacetime we study the reconstruction of a real scalar field as a product of two real fermion (so-called \textit{prime}) fields whose Fourier expansion exclusively contains prime modes. We undertake the canonical quantization of such prime fields and construct the corresponding Fock space by introducing creation operators $b_{p}^{\dag}$ --labeled by prime numbers $p$-- acting on the vacuum. The analysis of our model, based on the standard rules of quantum field theory and the assumption of the Riemann hypothesis, allow us to prove that the theory is not renormalizable. We also comment on the potential consequences of this result concerning the validity or breakdown of the Goldbach conjecture for large integer numbers. |
|
Title: Prime numbers, quantum field theory and the Goldbach conjecture. Authors: Miguel-Angel Sanchis-Lozano, J. Fernando Barbero G., Jose Navarro-Salas Journal-ref: Int.J.Mod.Phys. A27 (2012) 1250136 . Abstract: Motivated by the Goldbach conjecture in Number Theory and the abelian bosonization mechanism on a cylindrical two-dimensional spacetime we study the reconstruction of a real scalar field as a product of two real fermion (so-called \textit{prime}) fields whose Fourier expansion exclusively contains prime modes. We undertake the canonical quantization of such prime fields and construct the corresponding Fock space by introducing creation operators $b_{p}^{\dag}$ --labeled by prime numbers $p$-- acting on the vacuum. The analysis of our model, based on the standard rules of quantum field theory and the assumption of the Riemann hypothesis, allow us to prove that the theory is not renormalizable. We also comment on the potential consequences of this result concerning the validity or breakdown of the Goldbach conjecture for large integer numbers. |
Publicaciones 2011
|
Title: Introduction to modified gravity: from the cosmic speedup problem to quantum gravity phenomenology. Authors: Gonzalo J. Olmo Journal-ref: Chapter in the book Aspects of Today's Cosmology, Edited by Antonio Alfonso-Faus, ISBN 978-953-307-626-3. Abstract: These notes represent a summary of the introductory part of a course on modified gravity delivered at several Spanish Universities (Granada, Valencia, and Valladolid), at the University of Wisconsin-Milwaukee (WI, USA), and at the Karl-Franzens Universitaet (Graz, Austria) during the period 2008-2011. We begin with a discussion of the classical Newtonian framework and how special relativity boosted the interest on new theories of gravity. Then we focus on Nordstr\"om's scalar theories of gravity and their influence on Einstein's theory of general relativity. We comment on the meaning of the Einstein equivalence principle and its implications for the construction of alternative theories of gravity. We present the cosmic speedup problem and how $f(R)$ theories can be constrained attending to their weak-field behavior. We conclude by showing that Palatini $f(R)$ and $f(R,Q)$ theories can be used to address different aspects of quantum gravity phenomenology and singularity problems. |
|
Title: The Hawking signal in density-density correlations in BECs. Authors: Alessandro Fabbri Journal-ref: J.Phys.Conf.Ser. 314:012029,2011. Abstract: We outline the derivation of the Hawking quanta-partner signal in correlations, and highlight the specific application to detect it in density-density correlations in BECs. |
|
Title: Palatini Approach Beyond Einstein's Gravity. Authors: Gonzalo J. Olmo Journal-ref: Proceedings of FFP12. To appear. Abstract: I review recent results obtained for extensions of general relativity formulated within the Palatini formalism, an approach in which metric and connection are treated as independent geometrical entities. The peculiar dynamics of these theories, governed by second-order equations and having no new degrees of freedom, makes them specially suitable to address certain aspects of quantum gravity phenomenology, construct nonsingular bouncing cosmologies, and explore black hole interiors, which in the Reissner-Nordstr\"om case develop a compact core of finite density instead of a point-like singularity. |
|
Title: Nonsingular Black Holes Authors: Gonzalo J. Olmo and Diego Rubiera-García Abstract: We find that if general relativity is modified at the Planck scale by a Ricci-squared term, electrically charged black holes may be nonsingular. These objects concentrate their mass in a microscopic sphere of radius $r_{core}\approx N_q^{1/2}l_P/3$, where $l_P$ is the Planck length and $N_q$ is the number of electric charges. The singularity is avoided if the mass of the object satisfies the condition $M_0^2\approx m_P^2 \alpha_{em}^{3/2} N_q^3/2$, where $m_P$ is the Planck mass and $\alpha_{em}$ is the fine-structure constant. For astrophysical black holes this amount of charge is so small that their external horizon almost coincides with their Schwarzschild radius. We work within a first-order (Palatini) approach. |
|
Title: Palatini approach to bouncing cosmologies and DSR-like effects. Authors: Gonzalo J. Olmo Journal-ref: Proceedings of Loops'11, Madrid. To appear in Journal of Physics: Conference Series (JPCS) Abstract: It is shown that a quadratic gravitational Lagrangian in the Palatini formulation is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, in this theory field excitations propagating with different energy-densities perceive different background metrics, a fundamental characteristic of the DSR and Rainbow Gravity approaches. This theory, however, avoids the so-called soccer ball problem. Also, the resulting isotropic and anisotropic cosmologies are free from the big bang singularity. This singularity avoidance occurs non-perturbatively and shares some similitudes with the effective dynamics of loop quantum cosmology. |
|
Title: Metric-Palatini gravity unifying local constraints and late-time cosmic acceleration Authors: Tiberiu Harko, Tomi S. Koivisto, Francisco S.N. Lobo, Gonzalo J. Olmo Abstract: We present a novel approach to modified theories of gravity that consists of adding to the Einstein-Hilbert Lagrangian an f(R) term constructed a la Palatini. Using the respective dynamically equivalent scalar-tensor representation, we show that the theory can pass the Solar System observational constraints even if the scalar field is very light. This implies the existence of a long-range scalar field, which is able to modify the cosmological and galactic dynamics, but leaves the Solar System unaffected. We also verify the absence of instabilities in perturbations and provide explicit models which are consistent with local tests and lead to the late-time cosmic acceleration. |
|
Title: Palatini f(R) Black Holes in Nonlinear Electrodynamics. Authors: Gonzalo J. Olmo, D. Rubiera-Garcia. Abstract: The electrically charged Born-Infeld black holes in the Palatini formalism for $f(R)$ theories are analyzed. Specifically we study those supported by a theory $f(R)=R\pm R^2/R_P$, where $R_P$ is Planck's curvature. These black holes only differ from their General Relativity counterparts very close to the center, but may give rise to different geometrical structures in terms of inner horizons. The nature and strength of the central singularities are also significantly affected. In particular, for the model $f(R)=R - R^2/R_P$ the singularity is shifted to a finite radius, $r_+$, and the Kretschmann scalar diverges only as $1/(r-r_+)^{2}$. |
|
Title: Remarks on the renormalization of primordial cosmological perturbations. Authors: Ivan Agullo, Jose Navarro-Salas, Gonzalo J. Olmo, Leonard Parker Journal-ref: Phys. Rev. D 84, 107304 (2011) . 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 (momentum-space) renormalization in curved spacetime and address several misconceptions found in recent literature on this subject. |
|
Title: Non-singular Universes a la Palatini Authors: Gonzalo J. Olmo Journal-ref: J.Phys.Conf.Ser.314, 012054 (2011) . Abstract: It has recently been shown that f(R) theories formulated in the Palatini variational formalism are able to avoid the big bang singularity yielding instead a bouncing solution. The mechanism responsible for this behavior is similar to that observed in the effective dynamics of loop quantum cosmology and an f(R) theory exactly reproducing that dynamics has been found. I will show here that considering more general actions, with quadratic contributions of the Ricci tensor, results in a much richer phenomenology that yields bouncing solutions even in anisotropic (Bianchi I) scenarios. Some implications of these results are discussed. |
|
Title: Palatini Approach to Modified Gravity: f(R) Theories and Beyond Authors: Gonzalo J. Olmo Journal-ref: Int.J.Mod.Phys.D20, 413-462 (2011) . Abstract: We review the recent literature on modified theories of gravity in the Palatini approach. After discussing the motivations that lead to consider alternatives to Einstein's theory and to treat the metric and the connection as independent objects, we review several topics that have been recently studied within this framework. In particular, we provide an in-depth analysis of the cosmic speedup problem, laboratory and solar systems tests, the structure of stellar objects, the Cauchy problem, and bouncing cosmologies. We also discuss the importance of going beyond the f(R) models to capture other phenomenological aspects related with dark matter/energy and quantum gravity. |
|
Title: Hamiltonian Formulation of Palatini f(R) theories a la Brans-Dicke. Authors: Gonzalo J. Olmo and Hélios Sanchis-Alepuz Journal-ref: Phys.Rev.D83, 104036 (2011) . Abstract: We study the Hamiltonian formulation of f(R) theories of gravity both in metric and in Palatini formalism using their classical equivalence with Brans-Dicke theories with a non-trivial potential. The Palatini case, which corresponds to the w=-3/2 Brans-Dicke theory, requires special attention because of new constraints associated with the scalar field, which is non-dynamical. We derive, compare, and discuss the constraints and evolution equations for the ww=-3/2 and w\neq -3/2 cases. Based on the properties of the constraint and evolution equations, we find that, contrary to certain claims in the literature, the Cauchy problem for the w=-3/2 case is well-formulated and there is no reason to believe that it is not well-posed in general. |
|
Title: Palatini Actions and Quantum Gravity Phenomenology. Authors: Gonzalo J. Olmo Journal-ref: JCAP 10 (2011) 018 . Abstract: We show that a quadratic gravitational Lagrangian in the Palatini formulation is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, we show that in this theory field excitations propagating with different energy-densities perceive different background metrics, which is a fundamental characteristic of the DSR and Rainbow Gravity approaches. Also, the resulting isotropic and anisotropic cosmologies are free from the big bang singularity. This singularity avoidance occurs non-perturbatively and shares some similitudes with the effective dynamics of loop quantum cosmology. |