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Author  |
Capozziello, S.; Harko, T.; Koivisto, T.S.; Lobo, F.S.N.; Olmo, G.J. |
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Title |
Wormholes supported by hybrid metric-Palatini gravity |
Type |
Journal Article |
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Year |
2012 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
86 |
Issue |
12 |
Pages |
127504 - 5pp |
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Abstract |
Recently, a modified theory of gravity was presented, which consists of the superposition of the metric Einstein-Hilbert Lagrangian with an f(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. |
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Address |
[Capozziello, Salvatore] Univ Naples Federico II, Dipartimento Sci Fis, I-80126 Naples, Italy, Email: capozzie@na.infn.it; |
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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:000312446600010 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1280 |
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Author |
Capozziello, S.; Harko, T.; Lobo, F.S.N.; Olmo, G.J. |
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Title |
Hybrid Modified Gravity Unifying Local Tests, Galactic Dynamics and Late-Time Cosmic Acceleration |
Type |
Journal Article |
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Year |
2013 |
Publication |
International Journal of Modern Physics D |
Abbreviated Journal |
Int. J. Mod. Phys. D |
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Volume |
22 |
Issue |
12 |
Pages |
1342006 - 7pp |
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Keywords |
Modified gravity; late-time cosmic acceleration; dark matter; solar system tests |
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Abstract |
The nonequivalence between the metric and Palatini formalisms of f(R) gravity is an intriguing feature of these theories. However, in the recently proposed hybrid metric-Palatini gravity, consisting of the superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed a la Palatini, the “true” gravitational field is described by the interpolation of these two nonequivalent approaches. The theory predicts the existence of a light long-range scalar field, which passes the local constraints and affects the galactic and cosmological dynamics. Thus, the theory opens new possibilities for a unified approach, in the same theoretical framework, to the problems of dark energy and dark matter, without distinguishing a priori matter and geometric sources, but taking their dynamics into account under the same standard. |
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Address |
[Capozziello, Salvatore] Univ Naples Federico II, Dipartimento Fis, I-80126 Naples, Italy, Email: capozzie@na.infn.it; |
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Publisher |
World Scientific Publ Co Pte Ltd |
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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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ISSN |
0218-2718 |
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Notes |
WOS:000329048900013 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1688 |
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Author |
Capozziello, S.; Harko, T.; Lobo, F.S.N.; Olmo, G.J.; Vignolo, S. |
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Title |
The Cauchy problem in hybrid metric-Palatini f(X)-gravity |
Type |
Journal Article |
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Year |
2014 |
Publication |
International Journal of Geometric Methods in Modern Physics |
Abbreviated Journal |
Int. J. Geom. Methods Mod. Phys. |
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Volume |
11 |
Issue |
5 |
Pages |
1450042 - 12pp |
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Keywords |
Cauchy problem; modified gravity; hybrid metric-Palatini gravity |
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Abstract |
The well-formulation and the well-posedness of the Cauchy problem are discussed for hybrid metric-Palatini gravity, a recently proposed modified gravitational theory consisting of adding to the Einstein-Hilbert Lagrangian an f(R)-term constructed a la Palatini. The theory can be recast as a scalar-tensor one predicting the existence of a light long-range scalar field that evades the local Solar System tests and is able to modify galactic and cosmological dynamics, leading to the late-time cosmic acceleration. In this work, adopting generalized harmonic coordinates, we show that the initial value problem can always be well-formulated and, furthermore, can be well-posed depending on the adopted matter sources. |
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Address |
[Capozziello, Salvatore] Univ Naples Federico II, Dipartimento Sci Fis, Naples, Italy, Email: capozzie@na.infn.it; |
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Thesis |
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Publisher |
World Scientific Publ Co Pte 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 |
0219-8878 |
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:000336527100003 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1813 |
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Author |
Dias da Silva, L.F.; Lobo, F.S.N.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Photon rings as tests for alternative spherically symmetric geometries with thin accretion disks |
Type |
Journal Article |
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Year |
2023 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
108 |
Issue |
8 |
Pages |
084055 - 18pp |
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Keywords |
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Abstract |
The imaging by the Event Horizon Telescope (EHT) of the supermassive central objects at the heart of the M87 and Milky Way (Sgr A*) galaxies, has marked the first step into peering at the photon rings and central brightness depression that characterize the optical appearance of black holes surrounded by an accretion disk. Recently, Vagnozzi et al. [arXiv:2205.07787] used the claim by the EHT that the size of the shadow of Sgr A* can be inferred by calibrated measurements of the bright ring enclosing it, to constrain a large number of spherically symmetric space-time geometries. In this work we use this result to study some features of the first and second photon rings of a restricted pool of such geometries in thin accretion disk settings. The emission profile of the latter is described by calling upon three analytic samples belonging to the family introduced by Gralla, Lupsasca, and Marrone, in order to characterize such photon rings using the Lyapunov exponent of nearly bound orbits and discuss its correlation with the luminosity extinction rate between the first and second photon rings. We finally elaborate on the chances of using such photon rings as observational discriminators of alternative black hole geometries using very long baseline interferometry. |
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Address |
[Dias da Silva, Luis F.; Lobo, Francisco S. N.] Univ Lisbon, Inst Astrofis & Ciencias Espaco, Fac Ciencias, Edificio C8, P-1749016 Lisbon, Portugal, Email: fc53497@alunos.fc.ul.pt; |
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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 |
2470-0010 |
ISBN |
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Area |
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Conference |
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Notes |
WOS:001093442700002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5779 |
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| Permanent link to this record |
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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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Keywords |
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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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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:000302996100011 |
Approved |
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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| Permanent link to this record |
