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Author |
Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
The quantum, the geon and the crystal |
Type |
Journal Article |
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Year |
2015 |
Publication |
International Journal of Modern Physics D |
Abbreviated Journal |
Int. J. Mod. Phys. D |
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Volume |
24 |
Issue  |
9 |
Pages |
1542013 - 15pp |
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Keywords |
Effective geometries; crystalline structures; modified gravity; metric-affine approach; geons |
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Abstract |
Effective geometries arising from a hypothetical discrete structure of spacetime can play an important role in the understanding of the gravitational physics beyond General Relativity (GR). To discuss this question, we make use of lessons from crystalline systems within solid state physics, where the presence of defects in the discrete microstructure of the crystal determine the kind of effective geometry needed to properly describe the system in the macroscopic continuum limit. In this work, we study metric-affine theories with nonmetricity and torsion, which are the gravitational analog of crystalline structures with point defects and dislocations. We consider a crystal-motivated gravitational action and show the presence of topologically nontrivial structures (wormholes) supported by an electromagnetic field. Their existence has important implications for the quantum foam picture and the effective gravitational geometries. We discuss how the dialogue between solid state physics systems and modified gravitational theories can provide useful insights on both sides. |
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Address |
[Olmo, Gonzalo J.] Univ Valencia, CSIC, Fac Fis, Dept Fis Teor, E-46100 Valencia, Spain, Email: drubiera@fudan.edu.cn |
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Publisher |
World Scientific Publ Co Pte Ltd |
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English |
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ISSN |
0218-2718 |
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Notes |
WOS:000358793200014 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2322 |
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Author |
Guerrero, M.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Geodesic completeness of effective null geodesics in regular space-times with non-linear electrodynamics |
Type |
Journal Article |
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Year |
2023 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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Volume |
83 |
Issue |
9 |
Pages |
785 - 8pp |
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Abstract |
We study the completeness of light trajectories in certain spherically symmetric regular geometries found in Palatini theories of gravity threaded by non-linear (electromagnetic) fields, which makes their propagation to happen along geodesics of an effective metric. Two types of geodesic restoration mechanisms are employed: by pushing the focal point to infinite affine distance, thus unreachable in finite time by any sets of geodesics, or by the presence of a defocusing surface associated to the development of a wormhole throat. We discuss several examples of such geometries to conclude the completeness of all such effective paths. Our results are of interest both for the finding of singularity-free solutions and for the analysis of their optical appearances e.g. in shadow observations. |
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Address |
[Guerrero, Merce; Rubiera-Garcia, Diego] Univ Complutense Madrid, Dept Fis Teor, Madrid 28040, Spain, Email: merguerr@ucm.es; |
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Publisher |
Springer |
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English |
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ISSN |
1434-6044 |
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Notes |
WOS:001065963300005 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5710 |
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Author |
Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Nonsingular black holes in quadratic Palatini gravity |
Type |
Journal Article |
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Year |
2012 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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Volume |
72 |
Issue |
8 |
Pages |
2098 - 5pp |
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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) approximate to 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) approximate to m(P)(2)alpha N-3/2(em)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. |
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Address |
[Olmo, Gonzalo J.] Univ Valencia, Ctr Mixto, CSIC, Dept Fis Teor, E-46100 Valencia, Spain, Email: gonzalo.olmo@csic.es; |
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Publisher |
Springer |
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English |
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Series Volume |
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Edition |
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ISSN |
1434-6044 |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000308239900030 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ pastor @ |
Serial |
1138 |
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Author |
Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Nonsingular Charged Black Holes A La Palatini |
Type |
Journal Article |
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Year |
2012 |
Publication |
International Journal of Modern Physics D |
Abbreviated Journal |
Int. J. Mod. Phys. D |
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Volume |
21 |
Issue |
8 |
Pages |
1250067 - 6pp |
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Keywords |
Extended theories of gravity; Palatini formalism; Planck scale |
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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 (GR) 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. |
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Address |
[Olmo, Gonzalo J.] Univ Valencia, CSIC, Dept Fis Teor, Fac Fis, E-46100 Valencia, Spain |
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Corporate Author |
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Thesis |
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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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Series Editor |
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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 |
0218-2718 |
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:000308497500002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
no |
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Call Number |
IFIC @ pastor @ |
Serial |
1154 |
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Author |
Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Importance of torsion and invariant volumes in Palatini theories of gravity |
Type |
Journal Article |
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Year |
2013 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
88 |
Issue |
8 |
Pages |
084030 - 11pp |
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Keywords |
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Abstract |
We study the field equations of extensions of general relativity formulated within a metric-affine formalism setting torsion to zero (Palatini approach). We find that different (second-order) dynamical equations arise depending on whether torsion is set to zero (i) a priori or (ii) a posteriori, i.e., before or after considering variations of the action. Considering a generic family of Ricci-squared theories, we show that in both cases the connection can be decomposed as the sum of a Levi-Civita connection and terms depending on a vector field. However, while in case (i) this vector field is related to the symmetric part of the connection, in (ii) it comes from the torsion part and, therefore, it vanishes once torsion is completely removed. Moreover, the vanishing of this torsion-related vector field immediately implies the vanishing of the antisymmetric part of the Ricci tensor, which therefore plays no role in the dynamics. Related to this, we find that the Levi-Civita part of the connection is due to the existence of an invariant volume associated with an auxiliary metric h(mu v), which is algebraically related with the physical metric g(mu v). |
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Address |
[Olmo, Gonzalo J.] Ctr Mixto Univ Valencia CSIC, Dept Fis Teor, Valencia 46100, Spain, Email: gonzalo.olmo@csic.es; |
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Corporate Author |
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Thesis |
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Publisher |
Amer Physical Soc |
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 |
1550-7998 |
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:000326107300007 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1630 |
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