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Author |
Harko, T.; Koivisto, T.S.; Lobo, F.S.N.; Olmo, G.J. |
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Title |
Metric-Palatini gravity unifying local constraints and late-time cosmic acceleration |
Type |
Journal Article |
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Year |
2012 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
85 |
Issue |
8 |
Pages |
084016 - 5pp |
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Abstract |
We present a novel approach to modified theories of gravity which 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. |
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Address |
[Harko, Tiberiu] Univ Hong Kong, Dept Phys, Hong Kong, Hong Kong, Peoples R China, Email: harko@hkucc.hku.hk; |
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Amer Physical Soc |
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English |
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ISSN |
1550-7998 |
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Notes |
WOS:000302996100011 |
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no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
996 |
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Author |
Barragan, C.; Olmo, G.J. |
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Title |
Isotropic and anisotropic bouncing cosmologies in Palatini gravity |
Type |
Journal Article |
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Year |
2010 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
82 |
Issue |
8 |
Pages |
084015 - 15pp |
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Abstract |
We study isotropic and anisotropic (Bianchi I) cosmologies in Palatini f(R) and f(R, R μnu R μnu) theories of gravity with a perfect fluid and consider the existence of nonsingular bouncing solutions in the early universe. We find that all f(R) models with isotropic bouncing solutions develop shear singularities in the anisotropic case. On the contrary, the simple quadratic model R + aR(2)/R-P + R μnu R μnu/R-P exhibits regular bouncing solutions in both isotropic and anisotropic cases for a wide range of equations of state, including dust (for a<0) and radiation (for arbitrary a). It thus represents a purely gravitational solution to the big bang singularity and anisotropy problems of general relativity without the need for exotic (w>1) sources of matter/energy or extra degrees of freedom. |
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Address |
[Barragan, Carlos] Univ Autonoma Madrid, Dept Fis Teor, E-28049 Madrid, Spain, Email: gonzalo.olmo@uv.es |
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Amer Physical Soc |
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1550-7998 |
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Notes |
ISI:000282751900002 |
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no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ elepoucu @ |
Serial |
362 |
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Author |
Nascimento, J.R.; Olmo, G.J.; Porfirio, P.J.; Petrov, A.Y.; Soares, A.R. |
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Title |
Global monopole in Palatini f(R) gravity |
Type |
Journal Article |
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Year |
2019 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
99 |
Issue |
6 |
Pages |
064053 - 11pp |
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Abstract |
We consider the space-time metric generated by a global monopole in an extension of general relativity (GR) of the form f(R) = R – lambda R-2. The theory is formulated in the metric-affine (or Palatini) formalism, and exact analytical solutions are obtained. For lambda < 0, one finds that the solution has the same characteristics as the Schwarzschild black hole with a monopole charge in Einstein's GR. For lambda > 0, instead, the metric is more closely related to the Reissner-Nordstrom metric with a monopole charge and, in addition, it possesses a wormhole-like structure that allows for the geodesic completeness of the spacetime. Our solution recovers the expected limits when lambda = 0 and also at the asymptotic far limit. The angular deflection of light in this space-time in the weak field regime is also calculated. |
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Address |
[Nascimento, J. R.; Petrov, A. Yu; Soares, A. R.] Univ Fed Paraiba, Dept Fis, Caixa Postal 5008, BR-58051970 Joao Pessoa, Paraiba, Brazil, Email: jroberto@fisica.ufpb.br; |
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Amer Physical Soc |
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English |
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ISSN |
2470-0010 |
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Expedition |
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Conference |
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Notes |
WOS:000462920100010 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3966 |
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Permanent link to this record |
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Author |
Bejarano, C.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
What is a singular black hole beyond general relativity? |
Type |
Journal Article |
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Year |
2017 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
95 |
Issue |
6 |
Pages |
064043 - 18pp |
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Abstract |
Exploring the characterization of singular black hole spacetimes, we study the relation between energy density, curvature invariants, and geodesic completeness using a quadratic f(R) gravity theory coupled to an anisotropic fluid. Working in a metric-affine approach, our models and solutions represent minimal extensions of general relativity (GR) in the sense that they rapidly recover the usual Reissner-Nordstrm solution from near the inner horizon outwards. The anisotropic fluid helps modify only the innermost geometry. Depending on the values and signs of two parameters on the gravitational and matter sectors, a breakdown of the correlations between the finiteness/ divergence of the energy density, the behavior of curvature invariants, and the (in) completeness of geodesics is obtained. We find a variety of configurations with and without wormholes, a case with a de Sitter interior, solutions that mimic nonlinear models of electrodynamics coupled to GR, and configurations with up to four horizons. Our results raise questions regarding what infinities, if any, a quantum version of these theories should regularize. |
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Address |
[Bejarano, Cecilia] UBA, CONICET, IAFE, Casilla Correo 67,Sucursal 28, RA-1428 Buenos Aires, DF, Argentina, Email: cbejarano@iafe.uba.ar; |
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Amer Physical Soc |
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English |
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ISSN |
2470-0010 |
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Notes |
WOS:000399146000007 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3046 |
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Permanent link to this record |
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Author |
Nascimento, J.R.; Olmo, G.J.; Porfirio, P.J.; Petrov, A.Y.; Soares, A.R. |
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Title |
Nonlinear sigma-models in the Eddington-inspired Born-Infeld gravity |
Type |
Journal Article |
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Year |
2020 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
101 |
Issue |
6 |
Pages |
064043 - 11pp |
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Keywords |
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Abstract |
In this paper we consider two different nonlinear sigma-models minimally coupled to Eddington-inspired Born-Infeld gravity. We show that the resultant geometries represent minimal modifications with respect to those found in GR, though with important physical consequences. In particular, wormhole structures always arise, though this does not guarantee by itself the geodesic completeness of those space-times. In one of the models, quadratic in the canonical kinetic term, we identify a subset of solutions which are regular everywhere and are geodesically complete. We discuss characteristic features of these solutions and their dependence on the relationship between mass and global charge. |
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Address |
[Nascimento, J. R.; Porfirio, P. J.; Petrov, A. Yu; Soares, A. R.] Univ Fed Paraiba, Dept Fis, Caixa Postal 5008, BR-58051970 Joao Pessoa, Paraiba, Brazil, Email: jroberto@fisica.ufpb.br; |
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Amer Physical Soc |
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English |
Summary Language |
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ISSN |
2470-0010 |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000521099300008 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
4344 |
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Permanent link to this record |
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Author |
Bambi, C.; Cardenas-Avendano, A.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Wormholes and nonsingular spacetimes in Palatini f(R) gravity |
Type |
Journal Article |
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Year |
2016 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
93 |
Issue |
6 |
Pages |
064016 - 8pp |
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Keywords |
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Abstract |
We reconsider the problem of f(R) theories of gravity coupled to Born-Infeld theory of electrodynamics formulated in a Palatini approach, where metric and connection are independent fields. By studying electrovacuum configurations in a static and spherically symmetric spacetime, we find solutions which reduce to their Reissner-Nordstrom counterparts at large distances but undergo important nonperturbative modifications close to the center. Our new analysis reveals that the pointlike singularity is replaced by a finite-size wormhole structure, which provides a geodesically complete and thus nonsingular spacetime, despite the existence of curvature divergences at the wormhole throat. Implications of these results, in particular for the cosmic censorship conjecture, are discussed. |
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Address |
[Bambi, Cosimo; Rubiera-Garcia, D.] Fudan Univ, Ctr Field Theory & Particle Phys, 220 Handan Rd, Shanghai 200433, Peoples R China, Email: bambi@fudan.edu.cn; |
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Publisher |
Amer Physical Soc |
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English |
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ISSN |
2470-0010 |
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Expedition |
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Conference |
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Notes |
WOS:000371742700005 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2575 |
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Permanent link to this record |
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Author |
Magalhaes, R.B.; Crispino, L.C.B.; Olmo, G.J. |
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Title |
Compact objects in quadratic Palatini gravity generated by a free scalar field |
Type |
Journal Article |
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Year |
2022 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
105 |
Issue |
6 |
Pages |
064007 - 15pp |
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Keywords |
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Abstract |
We study the correspondence that connects the space of solutions of general relativity (GR) with that of Ricci-based gravity theories (RBGs) of the f(R, Q) type in the metric-affinc formulation, where Q = R(mu nu)R(mu nu). We focus on the case of scalar matter and show that when one considers a free massless scalar in the GR frame, important simplifications arise that allow one to establish the correspondence for arbitrary f (R, Q) Lagrangian. We particularize the analysis to a quadratic f (R, Q) theory and use the spherically symmetric, static solution of Jannis-Newman-Winicour as seed to generate new compact objects in our target theory. We find that two different types of solutions emerge, one representing naked singularities and another corresponding to asymmetric wormholes with bounded curvature scalars everywhere. The latter solutions, nonetheless, are geodesically incomplete. |
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Address |
[Magalhaes, Renan B.; Crispino, Luis C. B.] Univ Fed Para, Programa Posgrad Fis, BR-66075110 Belem, Para, Brazil, Email: renan.magalhaes@icen.ufpa.br; |
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Amer Physical Soc |
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English |
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ISSN |
2470-0010 |
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Conference |
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Notes |
WOS:000767103000006 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5171 |
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Permanent link to this record |
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Author |
Olmo, G.J.; Rubiera-Garcia, D.; Sanchez-Puente, A. |
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Title |
Accelerated observers and the notion of singular spacetime |
Type |
Journal Article |
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Year |
2018 |
Publication |
Classical and Quantum Gravity |
Abbreviated Journal |
Class. Quantum Gravity |
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Volume |
35 |
Issue |
5 |
Pages |
055010 - 18pp |
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Keywords |
general relativity; geodesic behaviour; black holes; spacetime singularities; modified theories of gravity |
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Abstract |
Geodesic completeness is typically regarded as a basic criterion to determine whether a given spacetime is regular or singular. However, the principle of general covariance does not privilege any family of observers over the others and, therefore, observers with arbitrary motions should be able to provide a complete physical description of the world. This suggests that in a regular spacetime, all physically acceptable observers should have complete paths. In this work we explore this idea by studying the motion of accelerated observers in spherically symmetric spacetimes and illustrate it by considering two geodesically complete black hole spacetimes recently described in the literature. We show that for bound and locally unbound accelerations, the paths of accelerated test particles are complete, providing further support to the regularity of such spacetimes. |
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Address |
[Olmo, Gonzalo J.; Sanchez-Puente, Antonio] Univ Valencia, Dept Fis Teor, CSIC, Ctr Mixto, E-46100 Valencia, Spain, Email: gonzalo.olmo@uv.es; |
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Publisher |
Iop Publishing Ltd |
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English |
Summary Language |
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Edition |
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ISSN |
0264-9381 |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000424042100001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3473 |
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Permanent link to this record |
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Author |
Bazeia, D.; Losano, L.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Geodesically complete BTZ-type solutions of 2+1 Born-Infeld gravity |
Type |
Journal Article |
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Year |
2017 |
Publication |
Classical and Quantum Gravity |
Abbreviated Journal |
Class. Quantum Gravity |
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Volume |
34 |
Issue |
4 |
Pages |
045006 - 21pp |
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Keywords |
Born-Infeld gravity; BTZ; wormholes; nonsingular solutions; geodesic completeness |
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Abstract |
We study Born-Infeld gravity coupled to a static, non-rotating electric field in 2 + 1 dimensions and find exact analytical solutions. Two families of such solutions represent geodesically complete, and hence nonsingular, spacetimes. Another family represents a point-like charge with a singularity at the center. Despite the absence of rotation, these solutions resemble the charged, rotating BTZ solution of general relativity but with a richer structure in terms of horizons. The nonsingular character of the first two families turn out to be attached to the emergence of a wormhole structure on their innermost region. This seems to be a generic prediction of extensions of general relativity formulated in metric-affine (or Palatini) spaces, where metric and connection are regarded as independent degrees of freedom. |
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Address |
[Bazeia, D.; Losano, L.; Olmo, Gonzalo J.] Univ Fed Paraiba, Dept Fis, BR-58051900 Joao Pessoa, Paraiba, Brazil, Email: bazeia@fisica.ufpb.br; |
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Publisher |
Iop Publishing Ltd |
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English |
Summary Language |
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ISSN |
0264-9381 |
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Conference |
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Notes |
WOS:000395398800002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3013 |
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Permanent link to this record |
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Author |
Guerrero, M.; Olmo, G.J.; Rubiera-Garcia, D.; Saez-Chillon Gomez, D. |
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Title |
Multiring images of thin accretion disk of a regular naked compact object |
Type |
Journal Article |
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Year |
2022 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
106 |
Issue |
4 |
Pages |
044070 - 13pp |
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Keywords |
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Abstract |
We discuss the importance of multiring images in the optical appearance of a horizonless spherically symmetric compact object, when illuminated by an optically thin accretion disk. Such an object corresponds to a subcase of an analytically tractable extension of the Kerr solution dubbed as the “eye of the storm” by Simpson and Visser in [J. Cosmol. Astropart. Phys. 03 (2022) 011], which merits in removing curvature singularities via an asymptotically Minkowski core, while harboring both a critical curve and an infinite potential barrier at the center for null geodesics. This multiring structure is induced by light rays winding several times around the object, and whose luminosity is significantly boosted as compared to the Schwarzschild solution by the modified shape of the potential. Using three toy profiles for the emission of an infinitely thin disk, truncated at its inner edge (taking its maximum value there) and having different decays with the distance, we discuss the image created by up to eight rings superimposed on top of the direct emission of the disk as its edge is moved closer to the center of the object. Our results point to the existence of multiring images with a non-negligible luminosity in shadow observations when one allows for the existence of other compact objects in the cosmic zoo beyond the Schwarzschild solution. Such multiring images could be detectable within the future projects on very long baseline interferometry. |
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Address |
[Guerrero, Merce; Rubiera-Garcia, Diego] Univ Complutense Madrid, Dept Fis Teor, IPARCOS, Madrid 28040, Spain, Email: merguerr@ucm.es; |
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Publisher |
Amer Physical Soc |
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English |
Summary Language |
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ISSN |
2470-0010 |
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Expedition |
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Conference |
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Notes |
WOS:000850772800006 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5352 |
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Permanent link to this record |