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Author |
Beltran Jimenez, J.; Heisenberg, L.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
On gravitational waves in Born-Infeld inspired non-singular cosmologies |
Type |
Journal Article |
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Year |
2017 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
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Volume |
10 |
Issue |
10 |
Pages |
029 - 23pp |
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Keywords |
alternatives to inflation; modified gravity; physics of the early universe; primordial gravitational waves (theory) |
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Abstract |
We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. We also investigate the role of the adiabatic sound speed of the matter sector in the regularisation of the gravitational waves evolution. We extend our analysis to more general Born-Infeld inspired theories where analogous solutions are found. As a general conclusion, we obtain that the bouncing solutions are generally more prone to instabilities, while the asymptotically Minkowski solutions can be rendered stable, making them appealing models for the early universe. |
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Address |
[Beltran Jimenez, Jose] Univ Toulon & Var, Aix Marseille Univ, CNRS, CPT, Marseille, France, Email: jose.beltran@uam.es; |
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Iop Publishing Ltd |
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English |
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1475-7516 |
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Notes |
WOS:000413332400002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3337 |
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Author |
Alfonso, V.I.; Bejarano, C.; Beltran Jimenez, J.; Olmo, G.J.; Orazi, E. |
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Title |
The trivial role of torsion in projective invariant theories of gravity with non-minimally coupled matter fields |
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 |
23 |
Pages |
235003 - 20pp |
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Keywords |
modified gravity; metric-affine theories; torsion; non-minimal couplings |
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Abstract |
We study a large family of metric-affine theories with a projective symmetry, including non-minimally coupled matter fields which respect this invariance. The symmetry is straightforwardly realised by imposing that the connection only enters through the symmetric part of the Ricci tensor, even in the matter sector. We leave the connection completely free (including torsion), and obtain its general solution as the Levi-Civita connection of an auxiliary metric, showing that the torsion only appears as a projective mode. This result justifies the widely used condition of setting vanishing torsion in these theories as a simple gauge choice. We apply our results to some particular cases considered in the literature, including the so-called Eddington-inspired-Born-Infeld theories among others. We finally discuss the possibility of imposing a gauge fixing where the connection is metric compatible, and comment on the genuine character of the non-metricity in theories where the two metrics are not conformally related. |
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Address |
[Alfonso, Victor I.] Univ Fed Campina Grande, Unidade Acad Fis, BR-58109970 Campina Grande, PB, Brazil, Email: viafonso@df.ufcg.edu.br; |
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Publisher |
Iop Publishing Ltd |
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English |
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0264-9381 |
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WOS:000414726500001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3353 |
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Author |
Afonso, V.I.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Scalar geons in Born-Infeld gravity |
Type |
Journal Article |
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Year |
2017 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
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Volume |
08 |
Issue |
8 |
Pages |
031 - 35pp |
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Keywords |
modified gravity; Wormholes |
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Abstract |
The existence of static, spherically symmetric, self-gravitating scalar field solutions in the context of Born-Infeld 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 Born-Infeld 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. |
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Address |
[Afonso, V. I.] Univ Fed Campina Grande, Unidade Acad Fis, BR-58109970 Campina Grande, PB, Brazil, Email: viafonso@df.ufcg.edu.br; |
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Publisher |
Iop Publishing Ltd |
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English |
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Abbreviated Series Title |
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Series Volume |
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ISSN |
1475-7516 |
ISBN |
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Expedition |
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Conference |
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Notes |
WOS:000408311900031 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3285 |
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Author |
Beltran Jimenez, J.; Heisenberg, L.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Born-Infeld inspired modifications of gravity |
Type |
Journal Article |
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Year |
2018 |
Publication |
Physics Reports |
Abbreviated Journal |
Phys. Rep. |
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Volume |
727 |
Issue |
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Pages |
1-129 |
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Keywords |
Born-Infeld gravity; Astrophysics; Black holes; Cosmology; Early universe; Compact objects; Singularities |
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Abstract |
General Relativity has shown an outstanding observational success in the scales where it has been directly tested. However, modifications have been intensively explored in the regimes where it seems either incomplete or signals its own limit of validity. In particular, the breakdown of unitarity near the Planck scale strongly suggests that General Relativity needs to be modified at high energies and quantum gravity effects are expected to be important. This is related to the existence of spacetime singularities when the solutions of General Relativity are extrapolated to regimes where curvatures are large. In this sense, Born-Infeld inspired modifications of gravity have shown an extraordinary ability to regularise the gravitational dynamics, leading to non-singular cosmologies and regular black hole spacetimes in a very robust manner and without resorting to quantum gravity effects. This has boosted the interest in these theories in applications to stellar structure, compact objects, inflationary scenarios, cosmological singularities, and black hole and wormhole physics, among others. We review the motivations, various formulations, and main results achieved within these theories, including their observational viability, and provide an overview of current open problems and future research opportunities. |
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Address |
[Beltran Jimenez, Jose] Univ Autonoma Madrid, CSIC, Inst Fis Teor, E-28049 Madrid, Spain, Email: jose.beltran@uam.es; |
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Publisher |
Elsevier Science Bv |
Place of Publication |
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English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0370-1573 |
ISBN |
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Conference |
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Notes |
WOS:000425482900001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3497 |
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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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Keywords |
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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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Publisher |
Amer Physical Soc |
Place of Publication |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
2470-0010 |
ISBN |
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Area |
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Expedition |
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Conference |
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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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Author |
Izadi, A.; Shacker, S.S.; Olmo, G.J.; Banerjee, R. |
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Title |
Observational effects of varying speed of light in quadratic gravity cosmological models |
Type |
Journal Article |
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Year |
2018 |
Publication |
International Journal of Geometric Methods in Modern Physics |
Abbreviated Journal |
Int. J. Geom. Methods Mod. Phys. |
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Volume |
15 |
Issue |
5 |
Pages |
1850084 - 16pp |
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Keywords |
Palatini formalism; modified gravity; causal structure constant; varying speed of light |
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Abstract |
We study different manifestations of the speed of light in theories of gravity where metric and connection are regarded as independent fields. We find that for a generic gravity theory in a frame with locally vanishing affine connection, the usual degeneracy between different manifestations of the speed of light is broken. In particular, the space-time causal structure constant (c(ST)) may become variable in that local frame. For theories of the form f(R, R-mu nu R-mu nu), this variation in c(ST) has an impact on the definition of the luminosity distance (and distance modulus), which can be used to confront the predictions of particular models against Supernovae type Ia (SN Ia) data. We carry out this test for a quadratic gravity model without cosmological constant assuming (i) a constant speed of light and (ii) a varying speed of light (VSL), and find that the latter scenario is favored by the data. |
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Address |
[Izadi, Azam] Khajeh Nasir Toosi Univ Technol, Dept Phys, Tehran, Iran, Email: aizadi@kntu.ac.ir; |
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Publisher |
World Scientific Publ Co Pte Ltd |
Place of Publication |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0219-8878 |
ISBN |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000429106400016 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3553 |
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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 |
Place of Publication |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0264-9381 |
ISBN |
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Area |
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Expedition |
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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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Author |
Bejarano, C.; Lobo, F.S.N.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Palatini wormholes and energy conditions from the prism of general relativity |
Type |
Journal Article |
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Year |
2017 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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Volume |
77 |
Issue |
11 |
Pages |
776 - 13pp |
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Keywords |
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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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Address |
[Bejarano, Cecilia] CONICET UBA, IAFE, Casilla Correo 67,Sucursal 28, RA-1428 Buenos Aires, DF, Argentina, Email: cbejarano@iafe.uba.ar; |
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Corporate Author |
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Thesis |
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Publisher |
Springer |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
1434-6044 |
ISBN |
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Conference |
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Notes |
WOS:000415697400001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3372 |
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Author |
Olmo, G.J.; Rubiera-Garcia, D.; Sanchez-Puente, A. |
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Title |
Impact of curvature divergences on physical observers in a wormhole space-time with horizons |
Type |
Journal Article |
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Year |
2016 |
Publication |
Classical and Quantum Gravity |
Abbreviated Journal |
Class. Quantum Gravity |
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Volume |
33 |
Issue |
11 |
Pages |
115007 - 12pp |
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Keywords |
Singularities; black holes; metric-affine geometry |
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Abstract |
The impact of curvature divergences on physical observers in a black hole space-time, which, nonetheless, is geodesically complete is investigated. This space-time is an exact solution of certain extensions of general relativity coupled to Maxwell's electrodynamics and, roughly speaking, consists of two Reissner-Nordstrom (or Schwarzschild or Minkowski) geometries connected by a spherical wormhole near the center. We find that, despite the existence of infinite tidal forces, causal contact is never lost among the elements making up the observer. This suggests that curvature divergences may not be as pathological as traditionally thought. |
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Address |
[Olmo, Gonzalo J.; Sanchez-Puente, A.] Univ Valencia, CSIC, Ctr Mixto, Dept Fis Teor, E-46100 Valencia, Spain, Email: gonzalo.olmo@csic.es; |
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Publisher |
Iop Publishing Ltd |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0264-9381 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000377442000010 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2728 |
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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 |
Place of Publication |
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Language |
English |
Summary Language |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
2470-0010 |
ISBN |
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Medium |
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Area |
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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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